Abstract

Upconverting erbium(III) complexes in N,N-dimethylformamide (DMF) were prepared via chloride ligand replacement by tetrafluoroborate, as suggested by changes in the spectral profile. Cl removal as precipitated salts was evidenced by X-ray diffraction (XRD) analysis. The systematic spectroscopic work indicated optimal condition for complex preparation. Ions in the coordination site were controlled by adjusting the water phase, thus the amount of removed chloride salts. Maximum emission intensity, lower red-to-green ratio and narrower emission lines were achieved at molar ratios Er3+:BF4− = 1:7 and H2O:DMF = 0.23. Studies extended to downshifted luminescence of Eu3+-complex provided more evidences of effective BF4 coordination, through dependence of relative intensities between 5D0 electric dipole and magnetic dipole (5D07F1) transitions. Infrared spectra suggest BF4 coordination to RE.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction

As an infrared (IR)-to-visible light conversion process, the upconversion luminescence (UCL) of rare-earth (RE) ions have been known for decades. This process is highly demanded for implementation of important photonic technologies in display systems [1], photovoltaics [2], multiplexed biosensing [3], diagnosis [4] and therapeutics [5]. The Energy Transfer Upconversion (ETU) involves the stepwise excitation among the discrete energy levels of RE ions by absorbing multiple infrared photons. The ETU mechanism is accepted as the most important in terms of relative efficiency among several two-photon upconversion processes, such as two-step absorption, cooperative sensitization, cooperative luminescence, second-harmonic generation, and two-photon absorption excitation [6]. The investigation on the basic mechanism for UCL was an active research field in the 1960’s. The fluorescence excited by two consecutive photons was first reported by Porter in 1961, who used two independent infrared sources to excite Pr3+ doped in a host lattice of LaCl3 [7]. Auzel in 1966 reported the upconverted emission of Er3+ ions in germanate oxide glasses [8,9]. In late 1980s, there was a boom of the UCL by the appearance of various fluoride glasses [10]. The second boom was leaded by the miniaturization of UCL phosphors to submicron-sized crystals, which opened the possibilities for applications as bioprobes as an alternative to conventional dye-based ones [11,12]. In 2004, first proposals of synthetic methods for nanoparticles were reported to prepare NaYF4 with reduced size (< 50 nm) [1315]. The reduced phonon energy of fluoride with respect to other hosts host improved the brightness [14]. All of those conventional materials are solid state inorganic crystals. Eventually, an organic system showing the UCL was reported for MOF (metal organic framework) in 2007 [16]. Even at this state, the UCL phenomenon was reported for “solid state” crystals.

Along with the development of the materials, various theories for understanding the UCL phenomenon had been proposed. Most important matter is the suppression of thermal relaxation of the intermediate energy levels during the multistep excitation. Since the solid-state system was ionic one, most of the theories are developed for ionic solid-state substances. In ionic solid materials, thermal vibrations of atoms surrounding optically active ions provide a field of phonons leading to luminescence quenching. The thermal relaxation, as a non-radiative relaxation process, is understood as multi phonon relaxation (MPR) based on the weak coupling between electrons and phonons for RE ions, approximated as:

$${W_{\textrm{MPR}}} = Bexp\left( { - \frac{{\mathrm{\Delta }E}}{{\hbar \mathrm{\omega }}}} \right),$$
where ℏω is the effective phonon energy to emit UCL and ΔE is the energy separation between excited energy level and the next lower one [17]. The discussions are mostly focused on the phonon energy value for deciding the required number of the phonons for the MPR since the system was “ionic”. On the other hand, electron phonon coupling (B) becomes more important in covalent system. The coupling consideration resembles to the selection rules of IR absorption. The IR absorption probability can be understood by considering the absorbing system as dynamic movement of electric dipole moments due to the movement of atoms, molecular vibration. Accordingly, the selection rule is decided by the value ∂μ/∂r, where μ is the electric dipole moment and r is the displacement of atoms due to the vibration [18]. Considering them, the worst “quenching” effect in aqueous system for the UCL is caused by the oscillation of O-H bond [19]. It is well known that the absorption around 3400 cm-1 is very strong. Compared to the phonon energy in the above-mentioned inorganic crystals, normally less than 1000 cm-1, the phonon energy is huge. Also, the dipole moment is very clear due to the ionicity, in other words, the localization of the charges. The high-energy vibrations of OH oscillators make this groups too “noisy” for suppressing the multistep excitation in UCL process. Considering organic system, hydrophobic system is much less “noisy” (i.e. lower vibrational frequencies) because of the less ionicity. The IR absorption coefficients are much less. If we select the surrounding of the RE ions to be the “silent” system, there is a possibility of the UCL in organic liquid.

Molecular based systems for UC luminescence, from organic ligands [2025] to the supramolecular level in metal–organic frameworks (MOF) [26,27] is an emerging research topic with few examples in the literature to date. The use of UC molecular composites for designing hybrid materials exhibit advantages over conventional solid-state compounds in terms of optical transparency and structural versatility [28]. On the other hand, improvements are necessary compensate the more pronounced influence of surrounding phonons in molecule-based system. The stabilization of the obtained complexes in a polymeric host with high hydrophobicity (water free) can overcome the thermal quenching of UC luminescence caused by OH oscillators present in aqueous environment [29]. In the case of UC-MOF, luminescent active RE ions are assembled in a porous organic material with well-organized structure, which is finally a solid-state crystalline host. The molecular systems face limitations to absorb more than a single photon and further populate higher excited state levels, because of their inherent high phonon energy caused by molecular vibrations, thus high probability of non-radiative processes [3032]. Therefore, the lifetime of RE excited-states when coordinated to organic ligands is expected to be short, reaching up to few microseconds [33]. For this reason, early examples of UC in molecular systems used double femtosecond laser beams for simultaneously pumping with extremely high-power density [34,35]. The formation of a shielding layer (e.g. fluorination or deuteration of ligands) around RE, aiming at protecting the ions from vibrating quenchers, have been proposed as an efficient strategy to extend the lifetime of intermediate excited levels [30]. In view of these facts, the rational design of UC luminescent materials implies shielding the RE ions from the effect of high-vibrational energy of OH oscillators, including water molecule. In this contribution, we describe the design of molecular complexes capable to emit UCL, which was guided by a systematic spectroscopic investigation for each type of complex prepared to unravel the grafted species. The obtained materials are intended for designing flexible and transparent luminescent materials, as an alternative to conventional solid-based ones. The strategy to minimize the emission intensity quenching was constructing a special layer around the emitter ions based on tetrafluoroborate as a coordinating ligand capable to replace the OH oscillators in the system, often coordinated to RE ions. We selected N,N-dimethylformamide as the system. The solubility parameter for the DMF is around 12 [36]. If the value is close to 8, as the case of cyclohexane, the system is too hydrophobic for not dissolving any ions. We dissolved erbium chloride and tetrafluoroborate salts (NH4BF4 or NaBF4) into DMF. The BF4 was a Cl replacing ligand for Er3+ in the system. By this process, we could observe green bright UCL in transparent liquid materials, which is useful for a further development of optoelectronic and photonic materials.

2. Experimental methods

2.1 Materials

Ammonium tetrafluoroborate, sodium tetrafluoroborate and dehydrated N,N-dimethylformamide were purchased from Wako Pure Chemical Industries (Osaka, Japan). Erbium (III) chloride hexahydrate and europium (III) chloride hexahydrate were purchased from Sigma-Aldrich (St Louis, MO, USA). Syringe filters (Nylon, 13 mm, 0.45 μm) were purchased from RephiQuik (Rephile Bioscience Ltd., Shanghai city, China).

2.2 Synthesis

The complexes were prepared by mixing rare-earth chlorides with tetrafluoroborate salts in DMF. The variations were performed in terms of: (i) the RE ion (Er3+ or Eu3+); (ii) the tetrafluoroborate salt (NH4BF4 or NaBF4); (iii) the initial molar ratio between the RE chloride and the tetrafluoroborate salt, RECl3:(NH4/Na)BF4 = 1:n (considering a fixed RECl3 concentration); and (iv) aqueous phase, according to the molar relation H2O:DMF. Table 1 summarizes these variables among samples.

Tables Icon

Table 1. Summary of set of complex samples and corresponding variables in terms of RE ion, tetrafluoroborate salt, molar ratio between RE chloride and tetrafluoroborate salt, and molar ratio between water and DMF.

In the first step of the synthesis, erbium(III) chloride hexahydrate solution in water (0.4 M, 0.2125 mL) was added to DMF (4 mL). Then, NH4BF4 powder (n eq) was added to the previous mixture containing ErCl3 (1 eq, 0.085 mmol) in order to obtain a molar ratio ErCl3:NH4BF4 = 1:n (n = 0, 5, 7, 10; i.e. 0, 44.6, 62.4 or 89.1 mg, respectively). The mixtures were sonicated for 40 min, followed by stirring at 300 rpm for 1h. The formed precipitate of NH4Cl was removed by using centrifugation at 2600 g for 5 min. The supernatants were filtered through a 0.45 μm membrane and allowed to react for further 4 days under gentle shaking motion (50 rpm).

In a similar way, the complexes were prepared using NaBF4 as the source of tetrafluoroborate anions, instead of the ammonium salt. First, erbium(III) chloride hexahydrate solution in water (1 eq, 0.085 mmol) was added to DMF (4 mL, 52 mmol). The initial concentration of ErCl3 in stock aqueous solution (i.e., before addition to DMF) varied as follows: 2.1, 0.7, 0.4 and 0.2 M. Therefore, in order to add 0.085 mmol of ErCl3 to DMF, the transferred volumes of such stock solutions were 0.040, 0.121, 0.213 and 0.425, respectively. In this sense, the water phase in DMF varied as follows: molar ratio H2O/DMF = 0.04, 0.13, 0.23 and 0.48, respectively. NaBF4 powder was then added (10 eq, 0.85 mmol, 93.3 mg) to obtain a molar ratio ErCl3:NaBF4 = 1:10. The mixtures were sonicated for 40 min followed by stirring at 300 rpm for 1h. The non-dissolved NaCl was removed by centrifugation (2600 g for 5 min) and filtration (0.45 μm membrane). The samples were maintained under gentle shaking motion (50 rpm) for 4 days.

The Eu3+-complexes were prepared in a similar way starting from europium(III) chloride hexahydrate solution in water (1 eq, 0.085 mmol, 0.4 M, 0.2125 mL) and DMF (4 mL, 52 mmol). Accordingly to this, the molar ratio H2O:DMF in the mixture was 0.23. Then, different amounts of NH4BF4 or NaBF4 were added in order to obtain the molar ratios EuCl3:(NH4/Na)BF4 1:n (n = 0, 5, 7, 10). As described above, samples undergone sonication (40 min) followed by stirring (300 rpm for 1h). The precipitated chloride salts were removed by centrifugation (2600 g for 5 min) and filtration (0.45 μm membrane). The samples were maintained under gentle shaking motion (50 rpm) for 4 days.

2.3 Characterization

UV-visible-NIR absorption spectra were measured using a spectrophotometer (V-770; JASCO, Tokyo, Japan). Luminescence spectra were obtained using a fluorescence spectrophotometer (RF-5300PC; Shimadzu Co., Kyoto, Japan). For measuring NIR-to-visible upconversion emission spectra, an external 980-nm excitation source, fibre-coupled laser diode (SP-976-5-1015-7 Laser Components, Ltd., Olching, Germany), was attached to the spectrophotometer. The impurity powder removed by centrifugation during synthesis was identified by X-ray powder diffraction (XRPD) using CuKα radiation (RINT-TTR III, RIGAKU, Japan). Fourier-transformed infrared (FTIR) spectra were measured on a FTIR spectrometer (FT/IR-6500; JASCO, Tokyo, Japan). Complex samples, NH4BF4 and NaBF4 were analyzed in KBr powder. The liquid complex samples were dropped and into KBr powder, the homogenized mixtures were oven-dried at 60 °C, and finally made into pellets. Quantifications of rare-earth elements, sodium and boron were performed by using inductively coupled plasma (ICP) emission spectrometry (ICPE-9000, Shimadzu Co., Kyoto, Japan). For the ICP determination, samples (100 μL) were digested in aqua regia (1 mL), a mixture of hydrochloric acid and nitric acids in a 3:1 molar ratio. The mixture was kept under stirring overnight and finally dissolved in water to a final volume of 10 mL. Serial dilutions of standard with concentrations of 0, 0.001, 0.01, 0.1 and 1 ppm were prepared from a multi-element calibration solutions with 5% aqueous HNO3 containing the elements: (i) Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sc, Sm, Tb, Th, Tm, Y, Yb (Multi-Element Calibration Standard 2, Perkin Elmer, Shelton, CT, USA); (ii) Al, B, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, K, Li, Mg, Mn, Na, Ni, Pb, Se, Sr, Te, Tl, Zn (PerkinElmer Pure VIII, Perkin Elmer, Shelton, CT, USA).

3. Results and discussion

3.1 Effect of BF4 coordinating ligand on UC luminescence

Luminescent complexes in liquid solution were obtained through the reaction of rare-earth chlorides and tetrafluoroborate precursors in N,N-dimethylformamide. The effect of BF4 coordinating ligand was investigated by analyzing complexes prepared at different molar ratios of ErCl3 and NH4BF4. The addition of NH4BF4 in excess has led to the precipitation of NH4Cl, as evidenced by XRD pattern shown in Fig. 8 in the Appendix. Absorption spectra from 400 to 1650 nm of Er3+-complexes prepared at different molar ratios of ErCl3:NH4BF4 (Fig.1a) show the Er3+ absorption band at 978 nm (4I15/24I11/2) suggesting the potential of the complex to upconvert 980 nm NIR light into visible emission. The peaks at 406, 442, 450, 488, 522, 542, 652 and 804 nm are assigned to Er3+ ion transitions from 4I15/2 to the levels: 2G9/2, 4F3/2, 4F5/2, 4F7/2, 2H11/2, 4S3/2, 4F9/2 and 4I9/2, respectively. The 1556 nm band, ascribed to the Er3+ transition 4I15/24I13/2, is overlapped with large water absorption band at around 1430 nm. A weak baseline rise was observed at shorter wavelengths as the concentration of BF4 increases, probably related to the scattering from coordination compounds. The photograph of samples (Fig. 1(b)) shows their transparency in the visible range.

 figure: Fig. 1.

Fig. 1. (a) UV–vis–NIR absorption spectra of complexes at different molar ratio of ErCl3:NH4BF4 and (b) photograph of the corresponding samples.

Download Full Size | PPT Slide | PDF

The UC emission spectra were recorded for complexes prepared at different molar ratio of ErCl3:NH4BF4 1:n (n = 0, 5, 7, 10) under 980-nm excitation (Fig. 2(a)). The photograph of a cuvette containing the Er3+-complex (ErCl3:NH4BF4 = 1:5) under 980 nm laser excitation is shown in Fig. 2(b). The energy-level diagram of Er3+ shown in Fig. 2(c) illustrates the mechanism of UC emission under 980 nm laser excitation. Upon NIR irradiation, a ground state absorption (GSA) promotes the Er3+ ion from the ground state 4I15/2 to the intermediate state 4I11/2. Then, an excited state absorption (ESA) occurs, in which another photon at 980 nm is absorbed promoting the ion to an even higher excited level 4F7/2. From this level, non-radiative relaxations occur to the levels 4S3/2, 2H11/2 and 4F9/2. The radiative decays to the 4I15/2 ground state result in the visible emissions at 525 nm, 550 nm and 660 nm. Alternatively, after absorbing the first photon, Er3+ may undergo a non-radiative relaxation from 4I11/2 level to the lower lying 4I13/2 level. The absorption of a second photon (ESA) promotes the ion to 4F9/2 level, from which the red upconverted emission is observed. The ESA is a mechanism for the UC luminescence involving an individual ion, which we consider to be the main process for the obtained complexes. Jia et al. [37] reported that at high concentration of Er3+, the energy transfer between two Er3+ ions occur as a consequence of their stronger interactions. In the case of a dominant ETU mechanism, the green emission is not observed, being the red one the only visible emission upon excitation at 980 nm.

 figure: Fig. 2.

Fig. 2. (a) UC emission spectra under 980-nm laser excitation (192 W/cm2) of Er3+-complexes at different molar ratio of ErCl3:NH4BF4. (b) Photograph of Er3+-complex (ErCl3:NH4BF4 = 1:5) in a cuvette under 980-nm irradiation. (b) Schematic energy-level diagram of Er3+ and mechanism of UC emissions under 980 nm laser excitation. (d) Red-to-green emission intensity ratio for different molar amounts of NH4BF4 (ErCl3:NH4BF4 1:n; n = 0, 5, 7, 10). Red and green emission intensities correspond to integrated areas in the ranges 630–680 nm and 509–576 nm, respectively.

Download Full Size | PPT Slide | PDF

The changes in the spectral shape in the red region (630–680 nm) between Er3+-complexes and ErCl3 (control sample ErCl3:NH4BF4 = 1:0) suggests a variation of the anion coordinated to Er3+ and allow us to propose that the BF4 ions were successfully grafted to Er3+ ions. Figure 2(d) depicts how intensity ratio between red and green emissions changes with the amount of NH4BF4 used for complex preparation. The red-to-green ratio values are higher in the presence of BF4 ions, and such value decreased by adding the NH4BF4 at a molar ratio ErCl3:NH4BF4=1:7, indicating the optimal condition to obtain the most efficient upconverting complex. This parameter is related to the multiphonon relaxation rate, since the red emission intensity increases to the detriment of the green one because of an increase of non-radiative decays from the levels 4S3/2 and 4I11/2 to the next lower ones 4F9/2 and 4I13/2, respectively. As described above in Eq. (1), WMPR is controlled by both electron-phonon coupling and phonon energy. After absorbing a NIR photon, the relaxation of excited electrons is influenced by the dynamic change of the electric dipole moment upon vibrational motions. Such effect is associated with the covalency of the metal-ligand bonding. The electric dipole moment is quite smaller in the case of covalent bonding, since the distance between the cation positive charges and covalent bonding electron is much closer than in the case of ionic bonding, in which the electrons are localized on the anions. Therefore, the weaker electrostatic interaction between RE and ligands reflects in a lower value of B parameter of Eq. (1), thus lower WMPR, and finally lower red-to-green ration is expected. In other words, the more surrounding bonding covalency, the higher radiative transition is expected. The replacement of Cl coordination by BF4 leads to a decrease in covalency character of the bonding with the ligands, because of the tetrahedral molecular geometry structure, and thus an increase in WMPR, as evidenced by the higher red-to-green ratio values for BF4-containing complexes [38]. Indeed, the WMPR for RE ions in a chloride host is expected to be many orders of magnitude lower than other hosts, as demonstrated by Soga et al. [39]. The shifted center of gravity for the red emission to longer wavelength (lower energy) after replacement of Cl by BF4, suggests an increase in ΔE of non-radiative transitions (4S3/24F9/2 and 4I11/24I13/2) and also reflects on the decreased covalency for BF4 ligands.

The higher emission intensity observed in presence of BF4 was unexpected considering the increased multiphonon relaxation rate (MPR) caused by such ligand. On the other hand, a relevant factor here is that Cl ligands were replaced by larger BF4 ligands. The degree of interaction of RE ions with ligands is modulated by their separation distance. The results indicate that in the absence of BF4, the OH oscillators would induce a more pronounced quenching effect, leading to lower intensity in the full wavelength range. The introduction of a larger ligand (BF4) can displace water from coordination in the inner sphere, and result in higher emission intensity in the full range. Therefore, suggesting the BF4 capacity to shield Er3+ from OH oscillators. In other words, BF4 located at inner coordination sphere, while water is possibly in a second coordination sphere.

3.2 Effect of water on the coordination environment and UC luminescence

In order to better control the coordination environment, Er3+-complexes were prepared from the reaction of erbium chloride with an excess of sodium tetrafluoroborate (ErCl3:NaBF4 = 1:10) at different hydration levels. Such reaction leads to the precipitation of sodium chloride. The removal of NaCl by centrifugation was confirmed by the X-ray diffraction pattern of the precipitate dry powder (Fig. 3(a)). The control over the amount of sodium and chlorine ions in the coordination site was performed by simply adjusting the initial water amount, thus the NaCl precipitation, as displayed in Fig. 3(b) of samples before purification by centrifugation. A transparent solution is observed at the highest water phase (H2O:DMF = 0.48), thus not being possible to remove Na+ and Cl ions by centrifugation. The samples became transparent after purification by centrifugation and filtration, as shown in Fig. 3(c). The concentrations of the elements Er, Na and B in purified samples were estimated by ICP (Fig. 3(d)). The results confirm that Na concentration increases (from 118 to 143 mM) at higher hydration levels. Concentrations of Er (20.2 ± 1.1 mM) and B (218.8 ± 6.3 mM) are similar among the samples. The concentration of B is around 10 times higher than Er, as expected.

 figure: Fig. 3.

Fig. 3. (a) X-ray powder diffraction (XRPD) pattern of precipitate collected by centrifugation and reference pattern of NaCl [40]. Photograph of samples prepared at different molar ratios of water (b) before and (c) after NaCl removal by centrifugation and filtration. Erbium, sodium and boron concentrations estimated by ICP as a function of molar ratio H2O:DMF for complexes prepared with ErCl3 and NaBF4. at different hydration levels. Error bars correspond to standard error of mean (n = 2).

Download Full Size | PPT Slide | PDF

The absorption spectra from 400 to 1650 nm of purified complexes prepared with ErCl3:NaBF4 = 1:10 at different water amounts (Fig. 4(a)) show the characteristic Er3+ absorption bands as previously mentioned. The water absorption at around 1430 nm increased linearly with the hydration level (Fig. 4(b)). The UC emission spectra of Er3+-complexes under 980-nm excitation (Fig. 4(c)) show the typical erbium emission bands centered around 525, 540 and 660 nm, corresponding to transitions from 2H11/2, 4S3/2 and 4F9/2 levels. The changes in the spectral shape among samples suggest a variation of the ligands coordinated to Er3+. Therefore, the different spectral shape of the purified samples (H2O:DMF = 0.04, 0.13, and 0.23) allow us to propose that the BF4 ions were successfully grafted to Er3+ ions after replacement of Cl. The obvious shift of the emission peaks at highest water amount (H2O:DMF = 0.48) indicated a change in the crystal field surrounding the erbium ions. An additional red emission at 630 nm is observed, which is overlapped with the emission at 660 nm, both attributed to 4F9/24I15/2 transitions [37,41]. UC emission broadening at highest hydration level indicates an inhomogeneous distribution of Er3+ site [41]. At a hydration level corresponding to H2O:DMF = 0.23 the maximum UC emission intensity is observed. Figure 4(d) shows the lowest red-to-green intensity ratio values of such sample reinforcing the idea of reaching at this hydration level the best ionic condition for charge stabilizing the upconverting complex, together with brighter luminescence and narrow emission lines. The increase of UCL intensity with water concentration, up to a certain hydration level, indicates that OH oscillators does not contribute linearly with the non-radiative deactivation of Er3+ excited states. This increase may be attributed to a more favorable ionic environment related, which hampers the direct coordination of water to RE ions. Na+ and Cl concentrations increase with the ratio H2O:DMF. As mentioned above, the Cl ions have lower contribution for MPR rate when compared with other hosts [39], and with respect to BF4 (Fig. 2). Therefore, the increase in emission intensity may be related to less Cl ligand substitution by BF4. The increased water amount also increases the presence of positive ions (Na+ in this case, or NH4+), which are possibly in a second coordination sphere and have an important role for keeping OH oscillators far enough from RE. The coordination structure seems to be stable up to a limit, indicated by broadening of emission lines at the highest hydration level investigated (0.48), which may be related to an ionic disorder, since purification step was not performed for this sample due to absence of NaCl precipitation. The quenching effect caused by water molecules was not so relevant as expected possibly because of a shielding shell of BF4−.

 figure: Fig. 4.

Fig. 4. (a) UV–vis–NIR absorption spectra of Er3+-complexes obtained from ErCl3 and NaBF4 reaction at different molar ratios between water and DMF. (b) Water absorption at 1440 nm as a function of hydration level. (c) UC emission spectra under 980-nm laser excitation (192 W/cm2) and their respective (d) red-to-green emission intensity ratios. Emission intensities correspond to integrated areas in the ranges 615–700 nm (red) and 500–575 nm (green).

Download Full Size | PPT Slide | PDF

3.3 Upconversion mechanism

The upconverting property of the Er3+-complex prepared with ErCl3 and NaBF4 at a molar ratio H2O:DMF = 0.23 was investigated by recording the UC emission spectra at different laser power (Fig. 5(a)). As discussed above, the main mechanism for the erbium UC luminescence in these single ion coordination complexes is ESA. In the UC process, the emission intensity (Iem) increases non-linearly with the pumping intensity (Iex), i.e. Iem α (Iex)n, where n is the number of NIR photons that are absorbed for the emission of a single visible photon. The value of n is obtained as the slope from the plot of the logarithm of Iem (which is the integrated area of the emissions) vs. the logarithm Iex (i.e. the laser power density). The n value is necessarily integer, however, the slope may decrease as a consequence of non-radiative processes, such as thermal effects. The values of n estimated for the Er3+ transitions 2H11/2 / 4S3/2 / 4F9/24I15/2 (Fig. 5(b)) suggests that two-photons are involved in such emission processes. Similar results for Er3+ UCL upon 980 nm excitation were reported in literature for ESA mechanism involving two IR photons in classical inorganic UC materials [42,43]. The non-linear UC processes via ESA mechanism involving the sequential absorption of two photons was reported for Tm salt in solution [35]. The observation of UCL via successive absorption of multiple photons is limited in molecular systems by their high phonon energy. The approach used to overcome short lifetime of RE intermediate excited stated in molecular systems is based shielding the RE ion from vibrational molecules, by fluorination or deuteration of local site [22]. The UC luminescence efficiency (i.e. the number of emitted visible photons divided by the number of the absorbed NIR photons) strongly depends on the excitation density due to the nonlinear nature of UC phenomenon [44]. The low absorption cross sections of f−f transitions in RE (approximately 10−20 cm2) drastically limit the UCL efficiency [45]. To overcome the small absorption cross-section, Hyppänen et al. [46] used an organic sensitizer IR-806 for sensitizing a nonlinear UC luminescence. The antenna effect under 806 nm irradiation has led to UCL via absorption of two photons at quite low power excitation density (5–6 W/cm2).

 figure: Fig. 5.

Fig. 5. (a) UC emission spectra of Er3+-complex recorded by pumping at 980 nm at different powers. (b) Emission intensity evolution as a function of laser power for different Er3+ transitions. Emission intensities correspond to integrated areas in the ranges 500–534 nm (2H11/24I15/2), 534–575 nm (4S3/24I15/2), and 625–700 nm (4F9/24I15/2).

Download Full Size | PPT Slide | PDF

3.4 Downshifting Eu3+-complexes

In order to better understand the coordination environment, complexes containing europium ions were prepared. Luminescence of Eu3+ gives important information about grafted species in the coordination sphere by analyzing transitions that are governed by the local ligand field [47]. The emission spectra of Eu3+-complexes prepared at different molar ratios EuCl3: EuCl3:(NH4/Na)BF4 = 1:n (n = 0, 5, 7, 10) at a fixed concentration of Eu3+ are shown in Fig. 6(a),b. The spectra were recorded under excitation at 394 nm, according to the maximum intensity recorded in the excitation spectra (Fig. 6(c) and Fig. 9(a,b) in the Appendix) and maximum absorbance in the UV–vis–NIR absorption spectra (Fig. 10 in Appendix), which corresponds to the Eu3+ transition 7F05L6. The Eu3+ energy level diagram showing the mechanism of downshifting emission under UV excitation is presented in Fig. 6(d). Upon 394-nm irradiation, the Eu3+ ion is excited to the 5L6 energy level. Non-radiative relaxations lead to the population of 5DJ manifold (J = 1 and 0) and then radiative transitions to 7FJ (J = 0–4) manifold result in the Eu3+ luminescence. The pure magnetic-dipole (MD) character of 5D07F1 transition allows its use as a reference, since it does not depend on the local ligand field [48]. Thus, the emission spectra were plotted by normalizing the emission intensity at 592 nm so that the same area is observed for MD transition (582–603 nm). Absence of change in shape of emission spectra among the samples allows us to consider the ligands chlorine and tetrafluoroborate as points of charge. The intensity of the hypersensitive electric dipolar transition 5D07F2 clearly changed with the amount of BF4. This result evidences the effect of BF4 in the in the local ligand field environment, since the 5D07F2 transition is related to partly covalent bonding and local polarization [48]. Figure 6(e) displays the integrated intensity ratio between 5D07F0–4 and MD transitions (ITOT / IMD) with variation in NH4BF4 or NaBF4 amounts. The relative intensity showed a dependence on BF4 concentration. The decrease in the relative intensity ITOT / IMD with temperature increase was demonstrated by Labrador-Páez et al. for Eu3+ aqueous complexes [49], which can be explained by an increase in WMPR. Therefore, as well as observed above for Er3+-complexes, the introduction of BF4 increases the probability of multiphonon relaxation. Moreover, the introduction of tetrafluoroborate anion have led to higher emission intensities (Fig. 6(f), non-normalized emission spectra presented in Fig. S2.c,d) with respect to the chloride complexes (control samples: EuCl3:(NH4/Na)BF4 = 1:0). Similarly as discussed above, this may be explained by the fact that Cl is smaller enough to allow the coordination of water molecules. The coordination of OH groups leads to non-radiative deexcitations due to their high vibrational mode. In the case of BF4, the larger ligand may displace water from the coordination sphere, leading to brighter complexes [49]. The complexes prepared with NaBF4 display higher emission intensity in comparison with those obtained from NH4BF4. The use of sodium salt allows to higher amount of precipitate (Fig. 11 in the Appendix), which means more efficient chloride removal. The more efficient ionic exchange of Cl by BF4 resulted in brighter complexes.

 figure: Fig. 6.

Fig. 6. Emission spectra (excitation at 394 nm) of Eu3+-complexes prepared with different amounts of (a) NH4BF4 or (b) NaBF4. Relative molar concentration EuCl3:(NH4/Na)BF4 1:n (n = 0, 5, 7, 10). (c) Photoexcitation spectrum of a Eu3+-complex (EuCl3:NaBF4 = 1:10) by monitoring the emission at 612 nm. (d) Energy-level diagram of Eu3+ and mechanism for downshifting emission under 394 nm excitation. (e) Integrated intensity ratio between total emission from 5D0 level (570–725 nm) with respect to MD emission (582–603 nm), and (f) integrated intensity in the full range (500–750 nm).

Download Full Size | PPT Slide | PDF

3.5 FTIR spectroscopy

The FTIR spectra of Er3+-complexes prepared with sodium and ammonium tetrafluoroborate salts are presented in Fig. 7 together with spectra of NaBF4 and NH4BF4 for comparison purposes. The characteristic vibrations of BF4 are present in all spectra at 1300, 1084, 772, 522 and 533 cm−1 [50,51]. The spectra of the ammonium-containing complex and NH4BF4 salt display a large band at around 3122 cm-1 and a peak at 1400 cm-1, which are assigned to NH4+ ions [52]. The large absorption band at around 3417 cm−1 is related to O-H stretching of water molecules [53]. The broad water absorption band observed in the spectra of liquid complexes (Fig. 1(a), Fig. 4(a) and Fig. 10) at around 1430 nm (ca. 7000 cm−1) corresponds to the first harmonic of such O-H absorption observed in FTIR spectra at ca. 3400 cm−1. Additional weak peaks in the spectra of complexes that do not appear in the spectra of tetrafluoroborate salts, located at 2992, 2780 and 1652 cm–1, are related to DMF. The main features in FTIR spectrum of neat DMF is the maximum absorption at 1683 cm–1, which is related to the high dipole moment of the carbonyl group, and highest frequency bands at 2930 cm-1 and 2858 cm-1 ­­due to C-H bonds of methyl and formyl groups, respectively [54]. The shift of carbonyl and formyl bands to lower wavenumbers may be due to lower strength of such bonds after coordination. The poor coordinating ability of BF4 allows for vacant coordination sites available for DMF involvement as coordinating solvent through these groups [53].

 figure: Fig. 7.

Fig. 7. FTIR spectra of Er3+-complexes prepared with tetrafluoroborate salts of sodium (ErCl3.NaBF4) and ammonium (ErCl3.NH4BF4), and spectra of salts NaBF4 and NH4BF4.

Download Full Size | PPT Slide | PDF

4. Conclusion

We concluded that upconversion luminescent coordination complex can be fabricated in organic solvent by adjusting the ionic environment. The effect of ligands chlorine and tetrafluoroborate on luminescence properties were discussed based on how their covalency affected the multiphonon relaxation rate. By analyzing the emission properties of both Er3+- and Eu3+-complexes, we have demonstrated that introduction of tetrafluoroborate induced a change in the local polarization, decreasing the covalency character of the coordination bonding. The larger BF4 ion may also contribute to shield RE ions from OH coordination. Counter cations of tetrafluoroborate salts, NH4+ and Na+, play an important role to remove Cl as a precipitate of NH4Cl or NaCl, thus improving the efficiency of BF4 grafting on RE ions. The use of sodium salt rendered brighter Eu3+-complexes. Moreover, control over the water phase was essential to obtain the optimal ionic environment for higher emission intensity, lower red-to-green ratio, and narrower emission lines. Complexation of RE with BF4 in DMF was confirmed by FTIR spectroscopy. The Er3+-complex obtained in this work showed excellent luminescent properties for NIR to visible upconversion luminescence. This work brings a novel approach to upconverting materials design, extending the possibilities to organic hosts and liquid systems. The promising results stimulates the development of new luminescent materials for optics and photonic applications. This finding is innovative since by adding soluble polymer to the DMF, one can possibly fabricate transparent polymer as a material for luminescent devices such as flexible displays.

Appendix 1

 figure: Fig. 8.

Fig. 8. X-ray powder diffraction pattern of precipitate collected by centrifugation and reference pattern of NH4Cl [55].

Download Full Size | PPT Slide | PDF

 figure: Fig. 9.

Fig. 9. Photoexcitation spectra by monitoring the emission at 612 nm (a,b) and emission spectra under excitation at 394 nm (c,d) of Eu3+-complexes prepared at different molar ratios of EuCl3:(NH4/Na)BF4 1:n (n = 0, 5, 7, 10).

Download Full Size | PPT Slide | PDF

 figure: Fig. 10.

Fig. 10. UV–vis–NIR absorption spectra in the ranges (a,c) from 350 to 1650 nm and (b,d) from 350 to 600 nm of Eu3+-complexes prepared with NH4BF4 (a,b) or NaBF4 (c,d) at different molar ratios EuCl3:(NH4/Na)BF4 = 1:n (n = 0, 5, 7, 10).

Download Full Size | PPT Slide | PDF

 figure: Fig. 11.

Fig. 11. Photograph of Eu3+-complexes prepared at different molar ratios EuCl3:(NH4/Na)BF4 = 1:n (n = 0, 5, 7, 10) before removal of (a) NH4Cl or (b) NaCl by centrifugation and filtration.

Download Full Size | PPT Slide | PDF

Funding

Ministry of Education, Culture, Sports, Science and Technology (15H05950, S1511012); Japan Science and Technology Agency.

Disclosures

The authors declare no conflicts of interest.

References

1. R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015). [CrossRef]  

2. D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018). [CrossRef]  

3. S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014). [CrossRef]  

4. D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014). [CrossRef]  

5. L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011). [CrossRef]  

6. F. Auzel, “Upconversion and anti-stokes processes with f and d ions in solids,” Chem. Rev. 104(1), 139–174 (2004). [CrossRef]  

7. J. F. Porter Jr, “Fluorescence excitation by the absorption of two consecutive photons,” Phys. Rev. Lett. 7(11), 414–415 (1961). [CrossRef]  

8. F. Auzel, “Compteur quantique par transfert d'energie entre deux ions de terres rares dans un tungstate mixte et dans un verre,” C. R. Acad. Sci. Paris 262, 1016–1019 (1966).

9. F. Auzel, “Compteur quantique par transfert d'energie de Yb3+ a Tm3+ dans un tungstate mixte et dans verre germanate,” C. R. Acad. Sci. Paris 263, 819–821 (1966).

10. R. S. Quimby, M. G. Drexhage, and M. J. Suscavage, “Efficient frequency up-conversion via energy transfer in fluoride glasses,” Electron. Lett. 23(1), 32–34 (1987). [CrossRef]  

11. H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999). [CrossRef]  

12. J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001). [CrossRef]  

13. G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004). [CrossRef]  

14. S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004). [CrossRef]  

15. H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004). [CrossRef]  

16. D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007). [CrossRef]  

17. R. C. Powell, “Physics of Solid-State Laser Materials,” (Springer, 1998).

18. B. Stuart, “Infrared Spectroscopy: Fundamentals and Applications,” (John Wiley & Sons, 2004).

19. A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999). [CrossRef]  

20. A. Hauser and C. Piguet, (2016). U.S. Patent No. 9,291,561. Washington, DC: U.S. Patent and Trademark Office.

21. L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011). [CrossRef]  

22. A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016). [CrossRef]  

23. B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019). [CrossRef]  

24. A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019). [CrossRef]  

25. B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020). [CrossRef]  .

26. X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016). [CrossRef]  

27. M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018). [CrossRef]  

28. D. W. Bruce, D. O’Hare, and R. I. Walton, Eds., “Molecular Materials” John Wiley & Sons14 (2011).

29. D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018). [CrossRef]  

30. Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016). [CrossRef]  

31. L. J. Charbonnière, “Bringing upconversion down to the molecular scale,” Dalton Trans. 47(26), 8566–8570 (2018). [CrossRef]  

32. A. M. Nonat and L. J. Charbonnière, “Upconversion of light with molecular and supramolecular lanthanide complexes,” Coord. Chem. Rev. 409, 213192 (2020). [CrossRef]  

33. C. Reinhard and H. U. Güdel, “High-resolution optical spectroscopy of Na3[Ln(dpa)3]·13H2O with Ln = Er3+, Tm3+, Yb3+,” Inorg. Chem. 41(5), 1048–1055 (2002). [CrossRef]  

34. X. Xiao, J. P. Haushalter, and G. W. Faris, “Upconversion from aqueous phase lanthanide chelates,” Opt. Lett. 30(13), 1674–1676 (2005). [CrossRef]  

35. O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012). [CrossRef]  

36. C. M. Hansen, “Solubility Parameters: A User’s Handbook,” (CRC Press, 2007).

37. R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006). [CrossRef]  

38. R. Reisfeld and N. Lieblich, “Optical spectra and relaxation of Eu+3 in germanate glasses,” J. Phys. Chem. Solids 34(9), 1467–1476 (1973). [CrossRef]  

39. K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003). [CrossRef]  

40. Y. I. Vesnin and S. N. Zakovrjashin, “About the decay of solid-solutions KCl-NaCl,” Solid State Commun. 31(9), 635–639 (1979). [CrossRef]  

41. L. V. Maneeshya, P. V. Thomas, and K. Joy, “Visible PL Emission from erbium doped BaTiO3 thin films deposited by RF magnetron sputtering,” Mater. Today: Proc. 2(3), 992–996 (2015). [CrossRef]  

42. J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004). [CrossRef]  

43. T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016). [CrossRef]  

44. G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014). [CrossRef]  

45. C. Strohhöfer and A. Polman, “Absorption and emission spectroscopy in Er3+–Yb3+ doped aluminum oxide waveguides,” Opt. Mater. 21(4), 705–712 (2003). [CrossRef]  

46. I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014). [CrossRef]  

47. S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998). [CrossRef]  

48. R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983). [CrossRef]  

49. L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018). [CrossRef]  

50. M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011). [CrossRef]  

51. H. D. Lutz, J. Himmrich, and M. J. Schmidt, “Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TICIO4, TIBF4, and NH4BF4 single crystals and of 11B-enriched NH4BF4,” J. Alloys Compd. 241(1-2), 1–9 (1996). [CrossRef]  

52. E. L. Wagner and D. F. Hornig, “The vibrational spectra of molecules and complex ions in crystals IV. Ammonium bromide and deutero-ammonium bromide,” J. Chem. Phys. 18(3), 305–312 (1950). [CrossRef]  

53. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Applications in Coordination, Organometallic and Bioinorganic Chemistry, 4th Edn. (John Wiley & Sons, Inc.).

54. N. Biliškov, “Infrared optical constants, molar absorption coefficients, dielectric constants, molar polarisabilities, transition moments and dipole moment derivatives of liquid N,N-dimethylformamide–carbon tetrachloride mixtures,” Spectrochim. Acta, Part A 79(2), 302–307 (2011). [CrossRef]  

55. B. K. Vainshtein, “Refinement of the structure of the group NH4 in the structure of ammonium chloride,” Tr. Inst. Kristallogr. Akad. Nauk SSSR. 12, 18–24 (1956).

References

  • View by:

  1. R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
    [Crossref]
  2. D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018).
    [Crossref]
  3. S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
    [Crossref]
  4. D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
    [Crossref]
  5. L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
    [Crossref]
  6. F. Auzel, “Upconversion and anti-stokes processes with f and d ions in solids,” Chem. Rev. 104(1), 139–174 (2004).
    [Crossref]
  7. J. F. Porter Jr, “Fluorescence excitation by the absorption of two consecutive photons,” Phys. Rev. Lett. 7(11), 414–415 (1961).
    [Crossref]
  8. F. Auzel, “Compteur quantique par transfert d'energie entre deux ions de terres rares dans un tungstate mixte et dans un verre,” C. R. Acad. Sci. Paris 262, 1016–1019 (1966).
  9. F. Auzel, “Compteur quantique par transfert d'energie de Yb3+ a Tm3+ dans un tungstate mixte et dans verre germanate,” C. R. Acad. Sci. Paris 263, 819–821 (1966).
  10. R. S. Quimby, M. G. Drexhage, and M. J. Suscavage, “Efficient frequency up-conversion via energy transfer in fluoride glasses,” Electron. Lett. 23(1), 32–34 (1987).
    [Crossref]
  11. H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
    [Crossref]
  12. J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
    [Crossref]
  13. G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
    [Crossref]
  14. S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004).
    [Crossref]
  15. H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
    [Crossref]
  16. D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
    [Crossref]
  17. R. C. Powell, “Physics of Solid-State Laser Materials,” (Springer, 1998).
  18. B. Stuart, “Infrared Spectroscopy: Fundamentals and Applications,” (John Wiley & Sons, 2004).
  19. A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
    [Crossref]
  20. A. Hauser and C. Piguet, (2016). U.S. Patent No. 9,291,561. Washington, DC: U.S. Patent and Trademark Office.
  21. L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
    [Crossref]
  22. A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
    [Crossref]
  23. B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019).
    [Crossref]
  24. A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
    [Crossref]
  25. B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020)..
    [Crossref]
  26. X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
    [Crossref]
  27. M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
    [Crossref]
  28. D. W. Bruce, D. O’Hare, and R. I. Walton, Eds., “Molecular Materials” John Wiley & Sons14 (2011).
  29. D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
    [Crossref]
  30. Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
    [Crossref]
  31. L. J. Charbonnière, “Bringing upconversion down to the molecular scale,” Dalton Trans. 47(26), 8566–8570 (2018).
    [Crossref]
  32. A. M. Nonat and L. J. Charbonnière, “Upconversion of light with molecular and supramolecular lanthanide complexes,” Coord. Chem. Rev. 409, 213192 (2020).
    [Crossref]
  33. C. Reinhard and H. U. Güdel, “High-resolution optical spectroscopy of Na3[Ln(dpa)3]·13H2O with Ln = Er3+, Tm3+, Yb3+,” Inorg. Chem. 41(5), 1048–1055 (2002).
    [Crossref]
  34. X. Xiao, J. P. Haushalter, and G. W. Faris, “Upconversion from aqueous phase lanthanide chelates,” Opt. Lett. 30(13), 1674–1676 (2005).
    [Crossref]
  35. O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
    [Crossref]
  36. C. M. Hansen, “Solubility Parameters: A User’s Handbook,” (CRC Press, 2007).
  37. R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006).
    [Crossref]
  38. R. Reisfeld and N. Lieblich, “Optical spectra and relaxation of Eu+3 in germanate glasses,” J. Phys. Chem. Solids 34(9), 1467–1476 (1973).
    [Crossref]
  39. K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
    [Crossref]
  40. Y. I. Vesnin and S. N. Zakovrjashin, “About the decay of solid-solutions KCl-NaCl,” Solid State Commun. 31(9), 635–639 (1979).
    [Crossref]
  41. L. V. Maneeshya, P. V. Thomas, and K. Joy, “Visible PL Emission from erbium doped BaTiO3 thin films deposited by RF magnetron sputtering,” Mater. Today: Proc. 2(3), 992–996 (2015).
    [Crossref]
  42. J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004).
    [Crossref]
  43. T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
    [Crossref]
  44. G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014).
    [Crossref]
  45. C. Strohhöfer and A. Polman, “Absorption and emission spectroscopy in Er3+–Yb3+ doped aluminum oxide waveguides,” Opt. Mater. 21(4), 705–712 (2003).
    [Crossref]
  46. I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
    [Crossref]
  47. S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998).
    [Crossref]
  48. R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
    [Crossref]
  49. L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
    [Crossref]
  50. M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
    [Crossref]
  51. H. D. Lutz, J. Himmrich, and M. J. Schmidt, “Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TICIO4, TIBF4, and NH4BF4 single crystals and of 11B-enriched NH4BF4,” J. Alloys Compd. 241(1-2), 1–9 (1996).
    [Crossref]
  52. E. L. Wagner and D. F. Hornig, “The vibrational spectra of molecules and complex ions in crystals IV. Ammonium bromide and deutero-ammonium bromide,” J. Chem. Phys. 18(3), 305–312 (1950).
    [Crossref]
  53. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Applications in Coordination, Organometallic and Bioinorganic Chemistry, 4th Edn. (John Wiley & Sons, Inc.).
  54. N. Biliškov, “Infrared optical constants, molar absorption coefficients, dielectric constants, molar polarisabilities, transition moments and dipole moment derivatives of liquid N,N-dimethylformamide–carbon tetrachloride mixtures,” Spectrochim. Acta, Part A 79(2), 302–307 (2011).
    [Crossref]
  55. B. K. Vainshtein, “Refinement of the structure of the group NH4 in the structure of ammonium chloride,” Tr. Inst. Kristallogr. Akad. Nauk SSSR. 12, 18–24 (1956).

2020 (2)

B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020)..
[Crossref]

A. M. Nonat and L. J. Charbonnière, “Upconversion of light with molecular and supramolecular lanthanide complexes,” Coord. Chem. Rev. 409, 213192 (2020).
[Crossref]

2019 (2)

B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019).
[Crossref]

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

2018 (5)

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

L. J. Charbonnière, “Bringing upconversion down to the molecular scale,” Dalton Trans. 47(26), 8566–8570 (2018).
[Crossref]

D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018).
[Crossref]

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

2016 (4)

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
[Crossref]

2015 (2)

L. V. Maneeshya, P. V. Thomas, and K. Joy, “Visible PL Emission from erbium doped BaTiO3 thin films deposited by RF magnetron sputtering,” Mater. Today: Proc. 2(3), 992–996 (2015).
[Crossref]

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

2014 (4)

S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
[Crossref]

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014).
[Crossref]

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

2012 (1)

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

2011 (4)

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

N. Biliškov, “Infrared optical constants, molar absorption coefficients, dielectric constants, molar polarisabilities, transition moments and dipole moment derivatives of liquid N,N-dimethylformamide–carbon tetrachloride mixtures,” Spectrochim. Acta, Part A 79(2), 302–307 (2011).
[Crossref]

2007 (1)

D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
[Crossref]

2006 (1)

R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006).
[Crossref]

2005 (1)

2004 (5)

J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004).
[Crossref]

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004).
[Crossref]

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

F. Auzel, “Upconversion and anti-stokes processes with f and d ions in solids,” Chem. Rev. 104(1), 139–174 (2004).
[Crossref]

2003 (2)

K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
[Crossref]

C. Strohhöfer and A. Polman, “Absorption and emission spectroscopy in Er3+–Yb3+ doped aluminum oxide waveguides,” Opt. Mater. 21(4), 705–712 (2003).
[Crossref]

2002 (1)

C. Reinhard and H. U. Güdel, “High-resolution optical spectroscopy of Na3[Ln(dpa)3]·13H2O with Ln = Er3+, Tm3+, Yb3+,” Inorg. Chem. 41(5), 1048–1055 (2002).
[Crossref]

2001 (1)

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

1999 (2)

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

1998 (1)

S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998).
[Crossref]

1996 (1)

H. D. Lutz, J. Himmrich, and M. J. Schmidt, “Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TICIO4, TIBF4, and NH4BF4 single crystals and of 11B-enriched NH4BF4,” J. Alloys Compd. 241(1-2), 1–9 (1996).
[Crossref]

1987 (1)

R. S. Quimby, M. G. Drexhage, and M. J. Suscavage, “Efficient frequency up-conversion via energy transfer in fluoride glasses,” Electron. Lett. 23(1), 32–34 (1987).
[Crossref]

1983 (1)

R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
[Crossref]

1979 (1)

Y. I. Vesnin and S. N. Zakovrjashin, “About the decay of solid-solutions KCl-NaCl,” Solid State Commun. 31(9), 635–639 (1979).
[Crossref]

1973 (1)

R. Reisfeld and N. Lieblich, “Optical spectra and relaxation of Eu+3 in germanate glasses,” J. Phys. Chem. Solids 34(9), 1467–1476 (1973).
[Crossref]

1966 (2)

F. Auzel, “Compteur quantique par transfert d'energie entre deux ions de terres rares dans un tungstate mixte et dans un verre,” C. R. Acad. Sci. Paris 262, 1016–1019 (1966).

F. Auzel, “Compteur quantique par transfert d'energie de Yb3+ a Tm3+ dans un tungstate mixte et dans verre germanate,” C. R. Acad. Sci. Paris 263, 819–821 (1966).

1961 (1)

J. F. Porter Jr, “Fluorescence excitation by the absorption of two consecutive photons,” Phys. Rev. Lett. 7(11), 414–415 (1961).
[Crossref]

1956 (1)

B. K. Vainshtein, “Refinement of the structure of the group NH4 in the structure of ammonium chloride,” Tr. Inst. Kristallogr. Akad. Nauk SSSR. 12, 18–24 (1956).

1950 (1)

E. L. Wagner and D. F. Hornig, “The vibrational spectra of molecules and complex ions in crystals IV. Ammonium bromide and deutero-ammonium bromide,” J. Chem. Phys. 18(3), 305–312 (1950).
[Crossref]

Ääritalo, T.

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

Aboshyan-Sorgho, L.

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

Aebischer, A.

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

Auzel, F.

F. Auzel, “Upconversion and anti-stokes processes with f and d ions in solids,” Chem. Rev. 104(1), 139–174 (2004).
[Crossref]

F. Auzel, “Compteur quantique par transfert d'energie entre deux ions de terres rares dans un tungstate mixte et dans un verre,” C. R. Acad. Sci. Paris 262, 1016–1019 (1966).

F. Auzel, “Compteur quantique par transfert d'energie de Yb3+ a Tm3+ dans un tungstate mixte et dans verre germanate,” C. R. Acad. Sci. Paris 263, 819–821 (1966).

Bahamyirou, S.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

Bai, Y.

R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006).
[Crossref]

Baran, J.

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Bator, G.

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Beeby, A.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Besnard, C.

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

Bettinelli, M.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Biliškov, N.

N. Biliškov, “Infrared optical constants, molar absorption coefficients, dielectric constants, molar polarisabilities, transition moments and dipole moment derivatives of liquid N,N-dimethylformamide–carbon tetrachloride mixtures,” Spectrochim. Acta, Part A 79(2), 302–307 (2011).
[Crossref]

Blackburn, O. A.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

Bonnet, J.

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

Brown, J. B.

K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
[Crossref]

Brown, R. N.

R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
[Crossref]

Bruce, D. W.

D. W. Bruce, D. O’Hare, and R. I. Walton, Eds., “Molecular Materials” John Wiley & Sons14 (2011).

Bu, W.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Bünzli, J. C. G.

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

Burton, J.

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

Bushby, L. M.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

Camerel, F.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

Chan, C. F.

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Charbonnière, L. J.

A. M. Nonat and L. J. Charbonnière, “Upconversion of light with molecular and supramolecular lanthanide complexes,” Coord. Chem. Rev. 409, 213192 (2020).
[Crossref]

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

L. J. Charbonnière, “Bringing upconversion down to the molecular scale,” Dalton Trans. 47(26), 8566–8570 (2018).
[Crossref]

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Chaussedent, S.

S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998).
[Crossref]

Chen, D.

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

Chen, G.

G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014).
[Crossref]

Chen, J.

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Chen, L.

J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004).
[Crossref]

Chen, R.

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

Chen, X.

G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014).
[Crossref]

D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
[Crossref]

Cheng, J.

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

Cheng, L.

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Clarkson, I. M.

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Coelho, G. R.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Cooper, D. E.

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

de Sousa, A. S.

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Del Longo, L.

S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998).
[Crossref]

Deng, R.

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

Dickins, R. S.

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Dos Santos, M. V.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Drexhage, M. G.

R. S. Quimby, M. G. Drexhage, and M. J. Suscavage, “Efficient frequency up-conversion via energy transfer in fluoride glasses,” Electron. Lett. 23(1), 32–34 (1987).
[Crossref]

R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
[Crossref]

Duan, N.

S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
[Crossref]

Eliseeva, S. V.

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

Fang, C. C.

S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
[Crossref]

Faris, G. W.

Faulkner, S.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Feng, X.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Ferrari, M.

S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998).
[Crossref]

Fu, Y.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Fürstenberg, A.

B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020)..
[Crossref]

B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019).
[Crossref]

García-Solé, J.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Ge, Y.

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

Golesorkhi, B.

B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020)..
[Crossref]

B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019).
[Crossref]

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

Greenberg, E.

R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
[Crossref]

Güdel, H. U.

C. Reinhard and H. U. Güdel, “High-resolution optical spectroscopy of Na3[Ln(dpa)3]·13H2O with Ln = Er3+, Tm3+, Yb3+,” Inorg. Chem. 41(5), 1048–1055 (2002).
[Crossref]

Güdel, H.-U.

S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004).
[Crossref]

Guénée, L.

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

Gul, S.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Guo, L. H.

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

Guo, L.-H.

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

Haase, M.

S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004).
[Crossref]

Hall, M.

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

Hampl, J.

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

Han, Y.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Hansen, C. M.

C. M. Hansen, “Solubility Parameters: A User’s Handbook,” (CRC Press, 2007).

Haro-González, P.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Hauser, A.

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

A. Hauser and C. Piguet, (2016). U.S. Patent No. 9,291,561. Washington, DC: U.S. Patent and Trademark Office.

Haushalter, J. P.

Heer, S.

S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004).
[Crossref]

Himmrich, J.

H. D. Lutz, J. Himmrich, and M. J. Schmidt, “Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TICIO4, TIBF4, and NH4BF4 single crystals and of 11B-enriched NH4BF4,” J. Alloys Compd. 241(1-2), 1–9 (1996).
[Crossref]

Hong, M.

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

Hornig, D. F.

E. L. Wagner and D. F. Hornig, “The vibrational spectra of molecules and complex ions in crystals IV. Ammonium bromide and deutero-ammonium bromide,” J. Chem. Phys. 18(3), 305–312 (1950).
[Crossref]

Hua, Y.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Huang, L.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Huang, W.

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

Hyppänen, I.

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

Iastrensk, M. F.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Jakubas, R.

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Jaque, D.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Jaque, F.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Jeannin, O.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

Jia, R.

R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006).
[Crossref]

Jiang, T.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Jin, L.

D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
[Crossref]

Jørgensen, C. K.

R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
[Crossref]

Joy, K.

L. V. Maneeshya, P. V. Thomas, and K. Joy, “Visible PL Emission from erbium doped BaTiO3 thin films deposited by RF magnetron sputtering,” Mater. Today: Proc. 2(3), 992–996 (2015).
[Crossref]

Kankare, J.

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

Kardos, K.

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

Kittilstved, K. R.

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

Kömpe, K.

S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004).
[Crossref]

Labrador-Páez, L.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Lahtinen, S.

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

Lecointre, A.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

Lee, S. T.

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Li, B.

X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
[Crossref]

Li, L.

D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
[Crossref]

Li, M.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Li, T.

R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006).
[Crossref]

Li, Y.

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Lieblich, N.

R. Reisfeld and N. Lieblich, “Optical spectra and relaxation of Eu+3 in germanate glasses,” J. Phys. Chem. Solids 34(9), 1467–1476 (1973).
[Crossref]

Liu, T.

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Liu, X.

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

Liu, Y.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Liu, Z.

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Lu, H.

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

Luo, X.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Lutz, H. D.

H. D. Lutz, J. Himmrich, and M. J. Schmidt, “Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TICIO4, TIBF4, and NH4BF4 single crystals and of 11B-enriched NH4BF4,” J. Alloys Compd. 241(1-2), 1–9 (1996).
[Crossref]

Ma, H.

X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
[Crossref]

Ma, P. C.

D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018).
[Crossref]

MacQueen, D. B.

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

Maia, L. J. Q.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Mäkelä, J.

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

Maneeshya, L. V.

L. V. Maneeshya, P. V. Thomas, and K. Joy, “Visible PL Emission from erbium doped BaTiO3 thin films deposited by RF magnetron sputtering,” Mater. Today: Proc. 2(3), 992–996 (2015).
[Crossref]

Manzani, D.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Medycki, W.

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Mély, Y.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

Mikeska, K. R.

K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
[Crossref]

Monteil, A.

S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998).
[Crossref]

Montes, E.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Mufti, N. A.

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

Nakamoto, K.

K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Applications in Coordination, Organometallic and Bioinorganic Chemistry, 4th Edn. (John Wiley & Sons, Inc.).

Natrajan, L. S.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

Ni, D.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Niedbala, R. S.

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

Nigoghossian, K.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Nonat, A.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Nonat, A. M.

A. M. Nonat and L. J. Charbonnière, “Upconversion of light with molecular and supramolecular lanthanide complexes,” Coord. Chem. Rev. 409, 213192 (2020).
[Crossref]

Nozary, H.

B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020)..
[Crossref]

B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019).
[Crossref]

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

O’Hare, D.

D. W. Bruce, D. O’Hare, and R. I. Walton, Eds., “Molecular Materials” John Wiley & Sons14 (2011).

Owczarek, M.

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Parker, D.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Pattison, P.

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

Pawlukojc, A.

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Pedroni, M.

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

Peng, W.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Petoud, S.

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

Piguet, C.

B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020)..
[Crossref]

B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019).
[Crossref]

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

A. Hauser and C. Piguet, (2016). U.S. Patent No. 9,291,561. Washington, DC: U.S. Patent and Trademark Office.

Platas-Iglesias, C.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Polman, A.

C. Strohhöfer and A. Polman, “Absorption and emission spectroscopy in Er3+–Yb3+ doped aluminum oxide waveguides,” Opt. Mater. 21(4), 705–712 (2003).
[Crossref]

Porter Jr, J. F.

J. F. Porter Jr, “Fluorescence excitation by the absorption of two consecutive photons,” Phys. Rev. Lett. 7(11), 414–415 (1961).
[Crossref]

Powell, R. C.

R. C. Powell, “Physics of Solid-State Laser Materials,” (Springer, 1998).

Prasad, P. N.

G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014).
[Crossref]

Przeslawski, J.

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Przybilla, F.

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

Qin, F.

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

Qiu, H.

G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014).
[Crossref]

Quimby, R. S.

R. S. Quimby, M. G. Drexhage, and M. J. Suscavage, “Efficient frequency up-conversion via energy transfer in fluoride glasses,” Electron. Lett. 23(1), 32–34 (1987).
[Crossref]

Reinhard, C.

C. Reinhard and H. U. Güdel, “High-resolution optical spectroscopy of Na3[Ln(dpa)3]·13H2O with Ln = Er3+, Tm3+, Yb3+,” Inorg. Chem. 41(5), 1048–1055 (2002).
[Crossref]

Reisfeld, R.

R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
[Crossref]

R. Reisfeld and N. Lieblich, “Optical spectra and relaxation of Eu+3 in germanate glasses,” J. Phys. Chem. Solids 34(9), 1467–1476 (1973).
[Crossref]

Ribeiro, S. J. L.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Riman, R. E.

K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
[Crossref]

Rong, T.

J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004).
[Crossref]

Royle, L.

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Schmidt, M. J.

H. D. Lutz, J. Himmrich, and M. J. Schmidt, “Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TICIO4, TIBF4, and NH4BF4 single crystals and of 11B-enriched NH4BF4,” J. Alloys Compd. 241(1-2), 1–9 (1996).
[Crossref]

Segatelli, M. G.

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

Shao, M.

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Shi, J.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Shi, Z.

S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
[Crossref]

Soga, K.

K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
[Crossref]

Sorensen, T. J.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

Soukka, T.

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

Strohhöfer, C.

C. Strohhöfer and A. Polman, “Absorption and emission spectroscopy in Er3+–Yb3+ doped aluminum oxide waveguides,” Opt. Mater. 21(4), 705–712 (2003).
[Crossref]

Stuart, B.

B. Stuart, “Infrared Spectroscopy: Fundamentals and Applications,” (John Wiley & Sons, 2004).

Suffren, Y.

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

Suscavage, M. J.

R. S. Quimby, M. G. Drexhage, and M. J. Suscavage, “Efficient frequency up-conversion via energy transfer in fluoride glasses,” Electron. Lett. 23(1), 32–34 (1987).
[Crossref]

Tanke, H. J.

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

Thom, J.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

Thomas, P. V.

L. V. Maneeshya, P. V. Thomas, and K. Joy, “Visible PL Emission from erbium doped BaTiO3 thin films deposited by RF magnetron sputtering,” Mater. Today: Proc. 2(3), 992–996 (2015).
[Crossref]

Tian, D.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Tian, Y.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Tropiano, M.

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

Vail, T.

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

Vainshtein, B. K.

B. K. Vainshtein, “Refinement of the structure of the group NH4 in the structure of ammonium chloride,” Tr. Inst. Kristallogr. Akad. Nauk SSSR. 12, 18–24 (1956).

Vesnin, Y. I.

Y. I. Vesnin and S. N. Zakovrjashin, “About the decay of solid-solutions KCl-NaCl,” Solid State Commun. 31(9), 635–639 (1979).
[Crossref]

Wagner, E. L.

E. L. Wagner and D. F. Hornig, “The vibrational spectra of molecules and complex ions in crystals IV. Ammonium bromide and deutero-ammonium bromide,” J. Chem. Phys. 18(3), 305–312 (1950).
[Crossref]

Walton, R. I.

D. W. Bruce, D. O’Hare, and R. I. Walton, Eds., “Molecular Materials” John Wiley & Sons14 (2011).

Wang, C.

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Wang, D. Y.

D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018).
[Crossref]

Wang, H.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Wang, S.

J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004).
[Crossref]

Wang, W.

K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
[Crossref]

Wang, Y.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Wang, Y. H.

D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018).
[Crossref]

Wang, Z.

S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
[Crossref]

Weng, D.

D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
[Crossref]

Williams, J. A. G.

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Wong, K. L.

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Wong, W. K.

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Wong, W. T.

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Woods, M.

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

Wright, W. H.

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

Wu, S.

S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
[Crossref]

Xiao, Q.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Xiao, X.

Xing, H.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Xing, M.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Yang, K.

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

Yang, W.

R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006).
[Crossref]

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

Yi, G.

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

Yin, L.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Yin, X.

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Yung-Mae, M. Y.

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

Zakovrjashin, S. N.

Y. I. Vesnin and S. N. Zakovrjashin, “About the decay of solid-solutions KCl-NaCl,” Solid State Commun. 31(9), 635–639 (1979).
[Crossref]

Zare, D.

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

Zhang, J.

J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004).
[Crossref]

Zhang, J. C.

D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018).
[Crossref]

Zhang, L.

X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
[Crossref]

Zhang, S.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Zhang, X.

X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
[Crossref]

Zhao, H.

X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
[Crossref]

Zhao, K.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Zhao, S.

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

Zheng, X.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
[Crossref]

Zhou, E.

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Zhou, L.

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Zijlmans, H. J. M. A. A.

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

ACS Appl. Energy Mater. (1)

D. Y. Wang, P. C. Ma, J. C. Zhang, and Y. H. Wang, “Efficient down-and up-conversion luminescence in Er3+–Yb3+ co-doped Y7O6F9 for photovoltaics,” ACS Appl. Energy Mater. 1(2), 447–454 (2018).
[Crossref]

ACS Appl. Mater. Interfaces (1)

X. Zhang, B. Li, H. Ma, L. Zhang, and H. Zhao, “Metal–organic frameworks modulated by doping Er3+ for up-conversion luminescence,” ACS Appl. Mater. Interfaces 8, 17389–17394 (2016).
[Crossref]

ACS Photonics (1)

I. Hyppänen, S. Lahtinen, T. Ääritalo, J. Mäkelä, J. Kankare, and T. Soukka, “Photon upconversion in a molecular lanthanide complex in anhydrous solution at room temperature,” ACS Photonics 1(5), 394–397 (2014).
[Crossref]

Adv. Funct. Mater. (1)

D. Ni, W. Bu, S. Zhang, X. Zheng, M. Li, H. Xing, Q. Xiao, Y. Liu, Y. Hua, L. Zhou, W. Peng, K. Zhao, and J. Shi, “Single Ho3+-doped upconversion nanoparticles for high-performance T2-weighted brain tumor diagnosis and MR/UCL/CT multimodal imaging,” Adv. Funct. Mater. 24(42), 6613–6620 (2014).
[Crossref]

Adv. Mater. (1)

S. Heer, K. Kömpe, H.-U. Güdel, and M. Haase, “Highly efficient multicolour upconversion emission in transparent colloids of lanthanide-doped NaYF4 nanocrystals,” Adv. Mater. 16(23-24), 2102–2105 (2004).
[Crossref]

Anal. Biochem. (2)

H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail, R. S. Niedbala, and H. J. Tanke, “Detection of cell and tissue surface antigens using up-converting phosphors: a new reporter technology,” Anal. Biochem. 267(1), 30–36 (1999).
[Crossref]

J. Hampl, M. Hall, N. A. Mufti, M. Y. Yung-Mae, D. B. MacQueen, W. H. Wright, and D. E. Cooper, “Upconverting phosphor reporters in immunochromatographic assays,” Anal. Biochem. 288(2), 176–187 (2001).
[Crossref]

Anal. Chem. (1)

S. Wu, N. Duan, Z. Shi, C. C. Fang, and Z. Wang, “Simultaneous aptasensor for multiplex pathogenic bacteria detection based on multicolor upconversion nanoparticles labels,” Anal. Chem. 86(6), 3100–3107 (2014).
[Crossref]

Angew. Chem., Int. Ed. (2)

L. Cheng, K. Yang, Y. Li, J. Chen, C. Wang, M. Shao, S. T. Lee, and Z. Liu, “Facile preparation of multifunctional upconversion nanoprobes for multimodal imaging and dual-targeted photothermal therapy,” Angew. Chem., Int. Ed. 50(32), 7385–7390 (2011).
[Crossref]

L. Aboshyan-Sorgho, C. Besnard, P. Pattison, K. R. Kittilstved, A. Aebischer, J. C. G. Bünzli, A. Hauser, and C. Piguet, “Near-infrared→visible light upconversion in a molecular trinuclear d–f–d complex,” Angew. Chem., Int. Ed. 50(18), 4108–4112 (2011).
[Crossref]

C. R. Acad. Sci. Paris (2)

F. Auzel, “Compteur quantique par transfert d'energie entre deux ions de terres rares dans un tungstate mixte et dans un verre,” C. R. Acad. Sci. Paris 262, 1016–1019 (1966).

F. Auzel, “Compteur quantique par transfert d'energie de Yb3+ a Tm3+ dans un tungstate mixte et dans verre germanate,” C. R. Acad. Sci. Paris 263, 819–821 (1966).

Chem. Phys. (1)

M. Owczarek, R. Jakubas, G. Bator, A. Pawlukojc, J. Baran, J. Przesławski, and W. Medycki, “Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by 1H NMR,” Chem. Phys. 381(1-3), 11–20 (2011).
[Crossref]

Chem. Phys. Lett. (1)

R. Reisfeld, E. Greenberg, R. N. Brown, M. G. Drexhage, and C. K. Jørgensen, “Fluorescence of europium (III) in a flouride glass containing zirconium,” Chem. Phys. Lett. 95(2), 91–94 (1983).
[Crossref]

Chem. Rev. (2)

G. Chen, H. Qiu, P. N. Prasad, and X. Chen, “Upconversion nanoparticles: Design, nanochemistry, and applications in theranostic,” Chem. Rev. 114(10), 5161–5214 (2014).
[Crossref]

F. Auzel, “Upconversion and anti-stokes processes with f and d ions in solids,” Chem. Rev. 104(1), 139–174 (2004).
[Crossref]

Chem. Sci. (1)

B. Golesorkhi, A. Fürstenberg, H. Nozary, and C. Piguet, “Deciphering and quantifying linear light upconversion in molecular erbium complexes,” Chem. Sci. 10(28), 6876–6885 (2019).
[Crossref]

Coord. Chem. Rev. (1)

A. M. Nonat and L. J. Charbonnière, “Upconversion of light with molecular and supramolecular lanthanide complexes,” Coord. Chem. Rev. 409, 213192 (2020).
[Crossref]

Dalton Trans. (2)

L. J. Charbonnière, “Bringing upconversion down to the molecular scale,” Dalton Trans. 47(26), 8566–8570 (2018).
[Crossref]

M. Li, S. Gul, D. Tian, E. Zhou, Y. Wang, Y. Han, L. Yin, and L. Huang, “Erbium(III)-based metal–organic frameworks with tunable upconversion emissions,” Dalton Trans. 47(37), 12868–12872 (2018).
[Crossref]

Electron. Lett. (1)

R. S. Quimby, M. G. Drexhage, and M. J. Suscavage, “Efficient frequency up-conversion via energy transfer in fluoride glasses,” Electron. Lett. 23(1), 32–34 (1987).
[Crossref]

Eur. J. Inorg. Chem. (1)

D. Weng, X. Zheng, X. Chen, L. Li, and L. Jin, “Synthesis, upconversion luminescence and magnetic properties of new lanthanide–organic frameworks with (43)2(46, 66, 83) topology,” Eur. J. Inorg. Chem. 2007(21), 3410–3415 (2007).
[Crossref]

Inorg. Chem. (2)

Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, and C. Piguet, “Taming lanthanide-centered upconversion at the molecular level,” Inorg. Chem. 55(20), 9964–9972 (2016).
[Crossref]

C. Reinhard and H. U. Güdel, “High-resolution optical spectroscopy of Na3[Ln(dpa)3]·13H2O with Ln = Er3+, Tm3+, Yb3+,” Inorg. Chem. 41(5), 1048–1055 (2002).
[Crossref]

J. Alloys Compd. (1)

H. D. Lutz, J. Himmrich, and M. J. Schmidt, “Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TICIO4, TIBF4, and NH4BF4 single crystals and of 11B-enriched NH4BF4,” J. Alloys Compd. 241(1-2), 1–9 (1996).
[Crossref]

J. Am. Ceram. Soc. (1)

J. Zhang, S. Wang, T. Rong, and L. Chen, “Upconversion luminescence in Er3+ doped and Yb3+/Er3+ codoped yttria nanocrystalline powders,” J. Am. Ceram. Soc. 87(6), 1072–1075 (2004).
[Crossref]

J. Am. Chem. Soc. (1)

A. Nonat, S. Bahamyirou, A. Lecointre, F. Przybilla, Y. Mély, C. Platas-Iglesias, F. Camerel, O. Jeannin, and L. J. Charbonnière, “Molecular upconversion in water in heteropolynuclear supramolecular Tb/Yb assemblies,” J. Am. Chem. Soc. 141(4), 1568–1576 (2019).
[Crossref]

J. Appl. Phys. (1)

K. Soga, W. Wang, R. E. Riman, J. B. Brown, and K. R. Mikeska, “Luminescent properties of nanostructured Dy3+-and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide,” J. Appl. Phys. 93(5), 2946–2951 (2003).
[Crossref]

J. Chem. Phys. (1)

E. L. Wagner and D. F. Hornig, “The vibrational spectra of molecules and complex ions in crystals IV. Ammonium bromide and deutero-ammonium bromide,” J. Chem. Phys. 18(3), 305–312 (1950).
[Crossref]

J. Chem. Soc., Perkin Trans. (1)

A. Beeby, I. M. Clarkson, R. S. Dickins, S. Faulkner, D. Parker, L. Royle, A. S. de Sousa, J. A. G. Williams, and M. Woods, “Non-radiative deactivation of the excited states of europium, terbium and ytterbium complexes by proximate energy-matched OH, NH and CH oscillators: an improved luminescence method for establishing solution hydration states,” J. Chem. Soc., Perkin Trans. 2(3), 493–504 (1999).
[Crossref]

J. Mater. Chem. (1)

H. Lu, G. Yi, S. Zhao, D. Chen, L.-H. Guo, and J. Cheng, “Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties,” J. Mater. Chem. 14(8), 1336–1341 (2004).
[Crossref]

J. Mater. Chem. C (1)

D. Manzani, K. Nigoghossian, M. F. Iastrensk, G. R. Coelho, M. V. Dos Santos, L. J. Q. Maia, S. J. L. Ribeiro, and M. G. Segatelli, “Luminescent silicone materials containing Eu3+-complexes for photonic applications,” J. Mater. Chem. C 6(30), 8258–8265 (2018).
[Crossref]

J. Phys. Chem. C (1)

L. Labrador-Páez, E. Montes, M. Pedroni, P. Haro-González, M. Bettinelli, D. Jaque, J. García-Solé, and F. Jaque, “Effect of H2O and D2O thermal anomalies on the luminescence of Eu3+ aqueous complexes,” J. Phys. Chem. C 122(26), 14838–14845 (2018).
[Crossref]

J. Phys. Chem. Solids (1)

R. Reisfeld and N. Lieblich, “Optical spectra and relaxation of Eu+3 in germanate glasses,” J. Phys. Chem. Solids 34(9), 1467–1476 (1973).
[Crossref]

Mater. Horiz. (1)

B. Golesorkhi, H. Nozary, A. Fürstenberg, and C. Piguet, “Erbium complexes as pioneers for implementing linear light-upconversion in molecules,” Mater. Horiz. 7, 1279–1296 (2020)..
[Crossref]

Mater. Today: Proc. (1)

L. V. Maneeshya, P. V. Thomas, and K. Joy, “Visible PL Emission from erbium doped BaTiO3 thin films deposited by RF magnetron sputtering,” Mater. Today: Proc. 2(3), 992–996 (2015).
[Crossref]

Nano Lett. (1)

G. Yi, H. Lu, S. Zhao, Y. Ge, W. Yang, D. Chen, and L. H. Guo, “Synthesis, characterization, and biological application of size-controlled nanocrystalline NaYF4:Yb,Er infrared-to-visible up-conversion phosphors,” Nano Lett. 4(11), 2191–2196 (2004).
[Crossref]

Nat. Commun. (1)

A. Nonat, C. F. Chan, T. Liu, C. Platas-Iglesias, Z. Liu, W. T. Wong, W. K. Wong, K. L. Wong, and L. J. Charbonnière, “Room temperature molecular up conversion in solution,” Nat. Commun. 7(1), 11978–8 (2016).
[Crossref]

Nat. Nanotechnol. (1)

R. Deng, F. Qin, R. Chen, W. Huang, M. Hong, and X. Liu, “Temporal full-colour tuning through non-steady-state upconversion,” Nat. Nanotechnol. 10(3), 237–242 (2015).
[Crossref]

Opt. Lett. (1)

Opt. Mater. (2)

R. Jia, W. Yang, Y. Bai, and T. Li, “Upconversion photoluminescence of ZrO2:Er3+ nanocrystals synthesized by using butadinol as high boiling point solvent,” Opt. Mater. 28(3), 246–249 (2006).
[Crossref]

C. Strohhöfer and A. Polman, “Absorption and emission spectroscopy in Er3+–Yb3+ doped aluminum oxide waveguides,” Opt. Mater. 21(4), 705–712 (2003).
[Crossref]

Philos. Mag. B (1)

S. Chaussedent, A. Monteil, M. Ferrari, and L. Del Longo, “Molecular dynamics study of Eu3+ in an aqueous solution: Luminescence spectrum from simulated environments,” Philos. Mag. B 77(2), 681–688 (1998).
[Crossref]

Phys. Chem. Chem. Phys. (1)

O. A. Blackburn, M. Tropiano, T. J. Sorensen, J. Thom, A. Beeby, L. M. Bushby, D. Parker, L. S. Natrajan, and S. Faulkner, “Luminescence and upconversion from thulium(III) species in solution,” Phys. Chem. Chem. Phys. 14(38), 13378–13384 (2012).
[Crossref]

Phys. Rev. Lett. (1)

J. F. Porter Jr, “Fluorescence excitation by the absorption of two consecutive photons,” Phys. Rev. Lett. 7(11), 414–415 (1961).
[Crossref]

RSC Adv. (1)

T. Jiang, M. Xing, Y. Tian, Y. Fu, X. Yin, H. Wang, X. Feng, and X. Luo, “Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation,” RSC Adv. 6(111), 109278 (2016).
[Crossref]

Solid State Commun. (1)

Y. I. Vesnin and S. N. Zakovrjashin, “About the decay of solid-solutions KCl-NaCl,” Solid State Commun. 31(9), 635–639 (1979).
[Crossref]

Spectrochim. Acta, Part A (1)

N. Biliškov, “Infrared optical constants, molar absorption coefficients, dielectric constants, molar polarisabilities, transition moments and dipole moment derivatives of liquid N,N-dimethylformamide–carbon tetrachloride mixtures,” Spectrochim. Acta, Part A 79(2), 302–307 (2011).
[Crossref]

Tr. Inst. Kristallogr. Akad. Nauk SSSR. (1)

B. K. Vainshtein, “Refinement of the structure of the group NH4 in the structure of ammonium chloride,” Tr. Inst. Kristallogr. Akad. Nauk SSSR. 12, 18–24 (1956).

Other (6)

K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B, Applications in Coordination, Organometallic and Bioinorganic Chemistry, 4th Edn. (John Wiley & Sons, Inc.).

A. Hauser and C. Piguet, (2016). U.S. Patent No. 9,291,561. Washington, DC: U.S. Patent and Trademark Office.

R. C. Powell, “Physics of Solid-State Laser Materials,” (Springer, 1998).

B. Stuart, “Infrared Spectroscopy: Fundamentals and Applications,” (John Wiley & Sons, 2004).

C. M. Hansen, “Solubility Parameters: A User’s Handbook,” (CRC Press, 2007).

D. W. Bruce, D. O’Hare, and R. I. Walton, Eds., “Molecular Materials” John Wiley & Sons14 (2011).

Cited By

Optica participates in Crossref's Cited-By Linking service. Citing articles from Optica Publishing Group journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (11)

Fig. 1.
Fig. 1. (a) UV–vis–NIR absorption spectra of complexes at different molar ratio of ErCl3:NH4BF4 and (b) photograph of the corresponding samples.
Fig. 2.
Fig. 2. (a) UC emission spectra under 980-nm laser excitation (192 W/cm2) of Er3+-complexes at different molar ratio of ErCl3:NH4BF4. (b) Photograph of Er3+-complex (ErCl3:NH4BF4 = 1:5) in a cuvette under 980-nm irradiation. (b) Schematic energy-level diagram of Er3+ and mechanism of UC emissions under 980 nm laser excitation. (d) Red-to-green emission intensity ratio for different molar amounts of NH4BF4 (ErCl3:NH4BF4 1:n; n = 0, 5, 7, 10). Red and green emission intensities correspond to integrated areas in the ranges 630–680 nm and 509–576 nm, respectively.
Fig. 3.
Fig. 3. (a) X-ray powder diffraction (XRPD) pattern of precipitate collected by centrifugation and reference pattern of NaCl [40]. Photograph of samples prepared at different molar ratios of water (b) before and (c) after NaCl removal by centrifugation and filtration. Erbium, sodium and boron concentrations estimated by ICP as a function of molar ratio H2O:DMF for complexes prepared with ErCl3 and NaBF4. at different hydration levels. Error bars correspond to standard error of mean (n = 2).
Fig. 4.
Fig. 4. (a) UV–vis–NIR absorption spectra of Er3+-complexes obtained from ErCl3 and NaBF4 reaction at different molar ratios between water and DMF. (b) Water absorption at 1440 nm as a function of hydration level. (c) UC emission spectra under 980-nm laser excitation (192 W/cm2) and their respective (d) red-to-green emission intensity ratios. Emission intensities correspond to integrated areas in the ranges 615–700 nm (red) and 500–575 nm (green).
Fig. 5.
Fig. 5. (a) UC emission spectra of Er3+-complex recorded by pumping at 980 nm at different powers. (b) Emission intensity evolution as a function of laser power for different Er3+ transitions. Emission intensities correspond to integrated areas in the ranges 500–534 nm (2H11/24I15/2), 534–575 nm (4S3/24I15/2), and 625–700 nm (4F9/24I15/2).
Fig. 6.
Fig. 6. Emission spectra (excitation at 394 nm) of Eu3+-complexes prepared with different amounts of (a) NH4BF4 or (b) NaBF4. Relative molar concentration EuCl3:(NH4/Na)BF4 1:n (n = 0, 5, 7, 10). (c) Photoexcitation spectrum of a Eu3+-complex (EuCl3:NaBF4 = 1:10) by monitoring the emission at 612 nm. (d) Energy-level diagram of Eu3+ and mechanism for downshifting emission under 394 nm excitation. (e) Integrated intensity ratio between total emission from 5D0 level (570–725 nm) with respect to MD emission (582–603 nm), and (f) integrated intensity in the full range (500–750 nm).
Fig. 7.
Fig. 7. FTIR spectra of Er3+-complexes prepared with tetrafluoroborate salts of sodium (ErCl3.NaBF4) and ammonium (ErCl3.NH4BF4), and spectra of salts NaBF4 and NH4BF4.
Fig. 8.
Fig. 8. X-ray powder diffraction pattern of precipitate collected by centrifugation and reference pattern of NH4Cl [55].
Fig. 9.
Fig. 9. Photoexcitation spectra by monitoring the emission at 612 nm (a,b) and emission spectra under excitation at 394 nm (c,d) of Eu3+-complexes prepared at different molar ratios of EuCl3:(NH4/Na)BF4 1:n (n = 0, 5, 7, 10).
Fig. 10.
Fig. 10. UV–vis–NIR absorption spectra in the ranges (a,c) from 350 to 1650 nm and (b,d) from 350 to 600 nm of Eu3+-complexes prepared with NH4BF4 (a,b) or NaBF4 (c,d) at different molar ratios EuCl3:(NH4/Na)BF4 = 1:n (n = 0, 5, 7, 10).
Fig. 11.
Fig. 11. Photograph of Eu3+-complexes prepared at different molar ratios EuCl3:(NH4/Na)BF4 = 1:n (n = 0, 5, 7, 10) before removal of (a) NH4Cl or (b) NaCl by centrifugation and filtration.

Tables (1)

Tables Icon

Table 1. Summary of set of complex samples and corresponding variables in terms of RE ion, tetrafluoroborate salt, molar ratio between RE chloride and tetrafluoroborate salt, and molar ratio between water and DMF.

Equations (1)

Equations on this page are rendered with MathJax. Learn more.

W MPR = B e x p ( Δ E ω ) ,

Metrics