Open Access
Add to BibSonomy
Abstract
This work investigates the near-infrared emission characteristics and energy transfer between erbium and cerium in bismuth glass by the reaction atmosphere process. The Er3+:1.5μm emission can be successfully enhanced by performing a reduction conversion of Ce4+→Ce3+ using a reducing atmosphere. The discrepancies of the energy structure between Ce3+ and Ce4+ result in a contrasting sensitizing effect on Er3+:1.5μm emission intensity and decay lifetime. The results show that a significant amount of Ce3+ is present in glasses prepared in a reducing atmosphere, whereas Ce4+ is the main species in an oxidizing atmosphere by means of absorption spectra and XPS curves. The reason for upconversion quenching is also discussed.
© 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Rare-earth (RE) doped luminescent materials have attracted much attention because of their numerous applications in optoelectronic technology, medical surgery and eye-safe laser radar [1–5]. In particularly, Er3+ doped materials could be helpful in silica glass to make better use of optical fiber amplifiers (OFA) in wavelength division multiplexing (WDM) transmission system [6, 7]. In recent years, with the urgent demands on increasing transmission capacity, it has been important to find a promising candidate to enhance the near infrared (NIR) emission replacing the conventional silica glass fiber. A great number of new materials, such as Er3+-doped bismuth oxide fiber [8], Er3+-doped tellurite oxide fiber [9] and Yb3+-doped silica glass fiber [10] were proposed for the high gain amplification performance of OFA. Among those candidates, bismuth-based Er3+-doped fiber (Bi-EDF) is the most effective candidate since it exhibits a broadband emission and negligible concentration quenching up to a high erbium concentration [11]. Juliet et al. have demonstrated that gains of 12 dB and higher are obtained over a bandwidth of 80 nm (1520-1600nm) from a 22.7cm Bi2O3-based EDFA [12].
In order to enhance Er3+:1.5μm emission, some RE ions, such as Yb3+, Ce3+, Tb3+ and Eu3+, are introduced as sensitizing co-dopant [7, 13–16]. The results show that Ce3+ is the most effective codopant to improve the 1.5μm band fluorescence by the cross relaxation (CR) process Er3+:4I11/2 + Ce3+:2F5/2→Er3+:4I13/2 + Ce3+:2F7/2 [13]. In particular, Ce exist in nature in the state of Ce4+. Ce has trivalent and four valent states [2]. The most popular model describes CeO2 as mixed-valence, which can be ascertained by the analysis of Ce 3d X-ray photoelectron spectroscopy (XPS) [17]. Generally, Ce3+ can be formed when synthesized in a reducing atmosphere, while Ce4+ exist when synthesized in an oxidizing atmosphere or an air atmosphere. Therefore, it has become necessary to investigate the energy transfer (ET) characteristics of Ce3+Ce4+ redox conversion in host since that the presence of Ce4+ can decrease the excitation energy and fluorescence intensity of Ce3+ [18]. The luminescent behavior of Ce4+ is controlled by the ligand-to-metal charge transfer of Ce4+-O- [19, 20].
Coexistence phenomenon of Ce4+ and Ce3+ in silicate glass have been found through their absorption and emission/excitation spectra [21]. Different synthesis atmospheres can result in different valent state to exist in host, and can control luminescence performance by complex ET interaction. A great number of articles associated with Er/Ce co-doped glass are focused on the characterization of their optical properties, but few works concerned the oxidized state of cerium in glass [7, 14–16, 22, 23]. The fundamental understanding of the valent state of cerium and how this key factor control luminescence properties of Er3+ doped glass is still lacking of experimental support. In this work, we co-dope bismuth glass with the same fixed amount of Er2O3 and CeO2 to explore how different synthesis atmospheres influence NIR fluorescence characteristics under 980nm excitation. XPS was used for evaluating the two oxidation states of Ce. Interestingly, cerium ion act as a sensitizing center to favor the Er3+:1.5μm emission using reducing synthesis atmosphere, and by contrast act as a quenching center to damage the Er3+:1.5μm emission using oxidizing synthesis atmosphere. A detailed study on absorption spectra, fluorescence spectra and time-resolved spectroscopy under 980nm excitation were carried out. In particular, the comparative study of ET mechanism from Er/Ce co-doped bismuth glass in reducing atmosphere and oxidizing atmosphere is also exhibited systematically.
2. Experimental
The set of glass used in this paper has the following nominal molar composition: 60Bi2O3-20B2O3-20SiO2-1Er2O3-xCeO2 (x = 0, 0.5, 1.0mol %). The raw materials were prepared from high-purity Bi2O3, B2O3, SiO2, Er2O3 and CeO2 powder. Well-mixed raw materials (20g) were placed in an alumina crucible and melted at 1050°C for 30 min in a reducing atmosphere (95%N2 + 5%H2) and an oxygen atmosphere (O2). Thus the samples are labeled as BBSErCe0N, BBSErCe0.5N, BBSErCe1.0N, BBSErCe0O, BBSErCe0.5O and BBSErCe1.0O, respectively. The melts were quickly poured into preheated stainless-steel molds and annealed for 2h near the glass transition temperature (Tg). The annealed sample was fabricated and polished to a size of 20 × 20 × 1mm3 for optical measurements.
The absorption spectra were recorded with a Perkin-Elmer Lambda 900UV/VIS/NIR spectrophotometer in 1-nm steps. The fluorescence spectra were measured by a TRIAX550 spectrophotometer with 980nm LD as the excitation sources. The decay curves were recorded by an FLSP920 instrument (Edinburgh instrument Ltd., UK). XPS spectra were obtained with a K-Alpha electron spectrometer (Thermo Fisher Scientific, USA) using a monochromatic Al source. All measurements were conducted at room temperature.
3. Results
3.1 Absorption spectra
Figure 1 shows the UV-Vis-NIR absorption spectra of bismuth glass doped with different CeO2 concentrations. Seven typical Er3+ absorption bands corresponding to the transitions from a ground state 4I15/2 to high levels are observed and labeled. By contrast, there is no obvious difference in the position and shape of its absorption bands with the CeO2 content, which confirms the sites of Er, Ce are homogenous distributed in bismuth glass network without cluster in the local surrounding.
Fig. 1 Absorption spectra of prepared samples; (a): the tailored UV-Vis absorption edge spectra, (b): the UV-Vis-NIR absorption spectra of samples with different CeO2 concentrations. The thickness of all samples is 1mm.
UV-Vis absorption spectroscopy is more helpful to study metal oxides to obtain information on different oxidation state of metal ions [24, 25]. A significant discrepancy occurred in the tail of UV-Vis absorption edge. The tailored spectra of this wavelength region have been exhibited in detail in Fig. 1(a). The BBSErCe0N and BBSErCe0O samples are shown to emphasize the Ce contribution to spectra. The synthesis atmosphere scarcely influences the absorption edge of CeO2-free sample. As shown in Fig. 1(a), the absorption edge of CeO2-free sample occurs at about 440nm due to the intrinsic bandgap absorption of glass host [15, 16]. With increasing CeO2 content, the absorption edge shows a red shift both using a reducing atmosphere and an oxidizing atmosphere. In particular, introduction of oxygen gas into glass melt apparently shifted the UV-Vis absorption edge toward the longer wavelength side compared to the nitrogen gas. Such a change becomes stronger in CeO2 high doped BBSErCe1.0O sample.
3.2 Fluorescence spectra, decay curves, and up-conversion (UC) luminescence pumped at 980 nm
CeO2 and synthesis gas are introduced in order to expect variation of the fluorescence emission spectrum. The near infrared fluorescence spectra of Ce3+, Er3+ doped glass pumped at 980nm are shown in Fig. 2. The emission spectra corresponding to 1mol% Er2O3 doped glass are similar to each other obtained both in reducing atmosphere and oxidizing atmosphere except the emission intensity. Moreover, the shape and position of spectra are also similar to those reported by Shen and Zhou for Er3+ ions doped matrix [15, 16]. The 1.5μm emission band corresponds to Er3+:4I13/2 →4I15/2 transition. This peak intensity is gradually enhanced with the increasing CeO2 content when fabricated in reducing atmosphere. The opposed changing trend is observed with CeO2 content in oxidizing atmosphere. To our knowledge, this phenomenon is scarcely reported in previous literature. The relative intensity ratios of 1.5μm emission are shown in Fig. 3. According to the Fuchtbauer–Ladenburg theory [26], the maximum simulated emission cross section (σem) at 1.5μm could be calculated to be 9.7 × 10−21 cm2, which is higher than that of silica-germanate glass (8.72 × 10−21cm2) and TeO2-ZnO-K2O glass (8.1 × 10−21cm2) [6, 27], and slightly lower than that of TeO2-BaO-La2O3 glass(9.97 × 10−21cm2) [28].
Fig. 3 Integrated areas of 1.5μm emission curves of Er3+:4I13/2 →4I15/2 transition for bismuth glass with different concentrations of Ce.
To further explore ET characteristics, the fluorescence decay curves for the Er3+:4I13/2 level in different concentrations of Ce in bismuth glass were measured and shown in Fig. 4. The decay curves were recorded with 980nm excitation wavelength. It can be fitted with a monoexponential function as:
where I(t) represents the emission intensity at time t, τ represents the lifetime and A represents a constant. The lifetime values of all samples are exhibited in Fig. 5. As shown in Fig. 4, the decay curves are found to follow a single exponential decay for Ce-free BBSErCe0N and BBSErCe0O samples. With the increasing CeO2 content, the decay curves present non-exponential behavior for samples whether in reducing atmosphere or in oxidizing atmosphere. Specifically, the lifetime of sample using oxidizing atmosphere decreases with Ce concentration, which demonstrates the same changing trend as that of 1.5μm emission intensity. However, the Er3+:4I13/2 lifetime increases with CeO2 concentration for concentration to 1.0mol%, see Fig. 5, which is consistent with the changing trend of its emission intensity for samples using reducing atmosphere. The similar phenomenon has been detected elsewhere [23, 29]. In these literatures, the measured lifetime follow the trend of emission intensity after the introduction of Ce, Yb ions. It must be noted that the changes on lifetime are moderately resulting from the addition of Ce.Fig. 4 Fluorescence decay curves for the Er3+:4I13/2 level in different concentrations of Ce in bismuth glass; (a): reducing atmosphere, (b): oxidizing atmosphere.
The UC luminescence spectra of the prepared samples under excitation at 980nm are shown in Fig. 6. The emission spectra of Er3+ single doped samples shows two main intense bands, at 553nm and 662nm, which correspond to transitions from the excited level to the 4I15/2 level of Er3+ configuration. Each assignment corresponding to the 4f-4f electronic transition is labeled for the present case. Among emission lines, the peak intensity at 553nm is predominantly intense, Moreover, these spectra are also similar to those obtained by Zhou et al. for Er3+/Ce3+ ions in glass matrix [14]. The incorporation of Ce ions into Er/Ce co-doped bismuth glass results in a quenching of the Er3+ emission intensity obtained under direct excitation of these ions, which exhibits a faster decrease of UC intensity than that obtained in previous literature, confirming the complex ET mechanism of Er-Ce centers [7, 14].
3.3 X-ray photoelectron spectroscopy studies
In order to provide further insights into photoluminescence behavior after the introduction of CeO2 in erbium doped glass, the selected samples with a high content of CeO2 (1mol%) were analyzed by means of XPS to detect possible chemical changes of cerium in the samples. The Ce3d XPS patterns are shown in Fig. 7. As a comparison, the XPS patterns of CeO2 raw materials were measured and added into this figure. Due to the trace amount of CeO2, the observed Ce3d XPS intensity signals are so weak that the spectral line can’t be deconvoluted. Therefore, the relative concentration of the two valent states of cerium (III and IV) could be roughly evaluated. Fortunately, the faint bands around 900eV and 882eV from BBSErCe1.0N and BBSErCe1.0O are still be distinguished. The binding energy of Ce3d XPS curves of BBSErCe1.0O is relative higher than that of BBSErCe1.0N, This suggests oxidation from Ce3+ to Ce4+ and thereby the amount ratio Ce3+/Ce4+ decreases using oxidizing atmosphere [30].
High resolution O1s core level spectrum of bismuth glass at different conditions can also reveal the oxidation states of cerium (shown in Fig. 8) [31]. According to the literature, two peaks at 529.6eV and 531.7eV are associated with oxygen species in CeO2 and Ce2O3, respectively [31, 32]. At the reducing synthesis condition, O1s XPS curve shifts from 530.58eV to 531.08eV with the increasing Ce content. However, the peak value of O1s XPS spectrum becomes lower from 531.18eV to 530.28eV with cerium content for samples using the oxidizing atmosphere. Therefore, the XPS results demonstrate that a large fraction of Ce ions in samples at reducing atmosphere are present as Ce3+ and then participate in the luminescence processes. When samples melted in oxidizing atmosphere, a great number of cerium ions exist as Ce4+, which has a significant influence on the photoluminescence of Er3+.
4. Discussions
4.1 Origin of the absorption edge
Absorption of Ce3+ originates from the allowed electric-dipole transition 4f→5d, leading to a strong absorption in the UV-Vis region [1, 33]. Absorption of Ce4+ is usually present owing to the charge transfer (CT) of Ce4+-O2- bond [24]. The photoluminescent performance of Ce3+, Ce4+ is strong dependent on the host matrix, doped concentration and synthesis conditions. As stated in section 3.1, for samples with same RE content, a great difference occurred at absorption edge results from the synthesis atmosphere. The red-shift of the UV-side absorption edge should own to the strong broadband absorption of Ce4+ in glass. Pure CeO2 demonstrates three absorption bands around 255nm, 285nm and 340nm. The latter two bands are assigned to Ce4+←O2- charge transfer and interband transitions, respectively [25]. The former band is ascribed to Ce3+←O2- charge transfer transition [34]. The similar absorption bands of Ce3+, Ce4+ have been observed in solutions and crystal lattice [18, 24, 25]. Based on the absorption wavelength order of Ce(III and IV), it is reasonable to deduce that the UV-Vis absorption edge shifts towards the longer wavelength as the conversion of Ce3+→Ce4+ oxidization reaction in glass. In addition, the absorption intensity of Ce4+ is significant higher than that of Ce3+, which makes a great contribution to the wavelength redshift of samples at oxidizing condition [18]. The assessment of valence change could be supported by mutual verification using UV-Vis absorption edge and XPS curves (Section 3.3).
4.2 ET mechanism between Er3+and Ce3+
The simplified energy level diagram of Er3+and Ce3+ and possible ET shortcuts are shown in Fig. 9. This diagram is helpful to understand the NIR emission spectra, fluorescence decay curves and UC luminescence of samples using reducing atmosphere. As stated in Section 3.2, the CeO2 codoping makes a great contribution to the increase of 1.5μm emission intensity and fluorescence lifetime. These behaviors are owing to the cross relaxation (CR) between Er3+ and Ce3+: Er3+:4I11/2 + Ce3+:2F5/2→Er3+:4I13/2 + Ce3+:2F7/2 [16, 23]. On the contrary, Ce3+ has a negative effect on UC luminescence (shown in Fig. 6). This is mainly due to the population migration from Er3+:4I11/2 level to Ce3+:2F7/2 level, leading to the decrease of population on Er3+: 4F7/2, 2H11/2, 4S3/2 and 4F9/2 excited state by the excited state absorption (ESA) and energy transfer upconversion (ETU).
4.3 ET mechanism between Er3+and Ce4+
Thanks to the facile reversibility redox couple (Ce4+/Ce3+) and elevated oxygen ion migration ability, it has been an important for many applications in material science and catalytic chemistry [35, 36]. Due to the effective 4f-5d excitation of Ce3+, it is also used to control the luminescence of other active ions by ET [30, 37]. The oxygen uptake/release could be realized by bubbling oxygen gas during the synthesis conditions [25]. This work is undertaken to investigate radiative & non-radiative nature of Er3+ in bismuth glass composed of cerium ions under different synthesis atmosphere.
Unlike the f-d transition of Ce3+, Ce4+ ions are characterized with the oxygen-metal charge transfer between the O2p and the Ce4f bands leading to the wide and strong absorption in UV-Vis spectral range [25, 38]. In particularly, the strong absorption can extend the UV-Vis absorption edge to 600nm in CeO2 pellet [20]. Unfortunately, no fixed energy level for Ce4+ exists and thereby the excited electrons relax to the ground state nonradiatively. The proposed energy level diagram of Ce4+ is shown in Fig. 10. The NIR emission spectra and decay curves of Er3+ under excitation at 980nm have been exhibited in section 3.2. The gradual decreasing intensity and lifetime with CeO2 for samples using oxidizing atmosphere indicate the quenching effect of Ce4+ by energy migration until luminescence is trapped [1].Many researchers have used the quenching effect of Ce3+/Ce4+ redox reaction as a “switch” on luminescence of active ions, such as Eu3+, Tb3+ [24, 30].
Two factors should be taken into consideration for ET mechanism between Er3+ and Ce4+. Firstly, due to the absence of 2F5/2, 2F7/2 levels, Ce4+ can’t feed the population on Er3+:4I13/2 level by the CR process. Secondly, due to the wide and strong absorption of charge transfer, the excited energy will be trapped into Ce4+ from the neighboring Er3+: 4F7/2, 2H11/2, 4S3/2 level reducing the pumping efficiency. The back ET from Ce4+ to Er3+ does not occur [39]. Little excited energy is driven to Er3+:4I13/2 level, resulting in the decrease of 1550nm emission intensity. In view of resonant ET process, the ET efficiency from Er3+ to Ce4+ is quite high along with the quenching of UC luminescence.
5. Conclusions
Er/Ce co-doped bismuth glasses with varying Ce concentration were successfully prepared in reducing atmosphere and oxidizing atmosphere for optical amplifier applications. By combining the information obtained from the UV-Vis absorption edge with that of XPS study, and in agreement with the theoretical work carried out on the energy structure of Ce4+, it is interpreted that significant amount of Ce3+ is present under reducing atmosphere. Mainly Ce4+ species are obtained in samples using the oxidizing atmosphere. Er/Ce co-doped samples prepared in reducing atmosphere exhibit the stronger emission intensity compared to that prepared in oxidizing atmosphere. Cross relaxation of Er3+:4I11/2 + Ce3+:2F5/2→Er3+:4I13/2 + Ce3+:2F7/2 feeds the population on Er3+:4I13/2 level to enlarge the 1.5μm fluorescence and lifetime. Meanwhile, the CR process leads to the quenching of UC luminescence. Due to the oxidation of Ce3+ to Ce4+ in oxidizing atmosphere, 1.5μm luminescence intensity and lifetime of Er/Ce co-doped glasses decreases gradually with the addition of Ce. This is because of the strong and wide absorption of charge transfer of Ce4+-O2-, which in turn quenches the UC luminescence of Er3+. Exploring the influence of oxidization state of cerium on Er3+:1.5μm emission is very beneficial to study the promising materials for amplifier.
Funding
National Natural Science Foundation of China (NSFC) (No. 61605115, 51472162, 51502022); Shanghai Sailing Project (No.15YF1411800); Shanghai Institutions of Higher Learning (No. TP2014061).
References and links
1. R. Fernandez-Gonzalez, J. J. Velazquez, V. D. Rodriguez, F. Rivera-Lopez, A. Lukowiak, A. Chiasera, M. Ferrari, R. R. Goncalves, J. Marrero-Jerez, F. Lahoz, and P. Nunez, “Luminescence and structural analysis of Ce3+ and Er3+ doped and Ce3+-Er3+ codoped Ca3Sc2Si3O12 garnets: influence of the doping concentration in the energy transfer processes,” RSC Advances 6(18), 15054–15061 (2016). [CrossRef]
2. T. Li, P. Li, Z. Wang, S. Xu, Q. Bai, and Z. Yang, “Coexistence phenomenon of Ce3+-Ce4+ and Eu2+-Eu3+ in Ce/Eu co-doped LiBaB9O15 phosphor: luminescence and energy transfer,” Phys. Chem. Chem. Phys. 19(5), 4131–4138 (2017). [CrossRef] [PubMed]
3. R. Zou, S. Gong, J. Shi, J. Jiao, K.-L. Wong, H. Zhang, J. Wang, and Q. Su, “Magnetic-NIR Persistent Luminescent Dual-Modal ZGOCS@MSNs@Gd2O3 Core–Shell Nanoprobes For In Vivo Imaging,” Chem. Mater. 29(9), 3938–3946 (2017). [CrossRef]
4. R. Zou, J. Huang, J. Shi, L. Huang, X. Zhang, K.-L. Wong, H. Zhang, D. Jin, J. Wang, and Q. Su, “Silica shell-assisted synthetic route for mono-disperse persistent nanophosphors with enhanced in vivo recharged near-infrared persistent luminescence,” Nano Res. 10(6), 2070–2082 (2017). [CrossRef]
5. B. M. Walsh, “Review of Tm and Ho materials; spectroscopy and lasers,” Laser Phys. 19(4), 855–866 (2009). [CrossRef]
6. T. Wei, F. Chen, Y. Tian, and S. Xu, “Broadband near-infrared emission property in Er3+/Ce3+ co-doped silica-germanate glass for fiber amplifier,” Spectrochim. Acta A Mol. Biomol. Spectrosc. 126, 53–58 (2014). [CrossRef] [PubMed]
7. F. Yang, B. Huang, L. Wu, Y. Zhou, F. Chen, G. Yang, and J. Li, “Enhanced 1.53μm radiative transition in Er3+/Ce3+ co-doped tellurite glass modified by B2O3 oxide,” Opt. Mater. 47, 149–156 (2015). [CrossRef]
8. S. Ohara and N. Sugimoto, “Bi2O3-based erbium doped fiber for short pulse amplification,” Opt. Mater. 31(9), 1280–1283 (2009). [CrossRef]
9. Y. Mori, Ohishi, M. Yamada, H. Ono, Y. Nishida, K. Oikawa, S. Sudo, 1.5µm Broadband Amplification by Tellurite-Based EDFAs, Conference on Optical Fiber Communications, Optical Society of America, Dallas, Texas, 1997, p. PD1.
10. P. F. Wysocki, N. Park, and D. Digiovanni, “Dual-stage erbium-doped, erbium/ytterbium-codoped fiber amplifier with up to +26-dBm output power and a 17-nm flat spectrum,” Opt. Lett. 21(21), 1744–1746 (1996). [CrossRef] [PubMed]
11. N. Sugimoto, “Ultrafast Optical Switches and Wavelength Division Multiplexing (WDM) Amplifiers Based on Bismuth Oxide Glasses,” J. Am. Ceram. Soc. 85(5), 1083–1088 (2002). [CrossRef]
12. J. T. Gopinath, H. Sotobayashi, and E. P. Ippen, Picosecond pulse amplification over a bandwidth of 80 nm in a 23 cm length of Bi2O3-based Erbium-doped fiber, Optical Amplifiers and Their Applications, Optical Society of America, Otaru, 2003, p. MD23.
13. B. Huang, Y. Zhou, F. Yang, L. Wu, Y. Qi, and J. Li, “The 1.53μm spectroscopic properties of Er3+/Ce3+/Yb3+ tri-doped tellurite glasses containing silver nanoparticles,” Opt. Mater. 51, 9–17 (2016). [CrossRef]
14. Y. Zhou, N. Gai, and J. Wang, “Comparative investigation on spectroscopic properties of Er3+ between Ce3+-doped and B2O3-added bismuth glasses,” J. Phys. Chem. Solids 70(2), 261–265 (2009). [CrossRef]
15. Y. Zhou, S. Wang, J. Lin, M. Ye, and G. Yang, “Effect of Ce3+ codoping on Er3+-doped bismuth-germanate glass and fiber under 980nm excitation,” Opt. Commun. 284(9), 2312–2316 (2011). [CrossRef]
16. X. Shen, Q. Nie, T. Xu, S. Dai, G. Li, and X. Wang, “Effect of Ce3+ on the spectroscopic properties in Er3+ doped TeO2–GeO2–Nb2O5–Li2O glasses,” J. Lumin. 126(2), 273–277 (2007). [CrossRef]
17. S. Aškrabić, Z. D. Dohčević-Mitrović, V. D. Araújo, G. Ionita, J. M. M. de Lima Jr, and A. Cantarero, “F-centre luminescence in nanocrystalline CeO2,” J. Phys. D Appl. Phys. 46(49), 495306 (2013). [CrossRef]
18. G. Özen and B. Demirata, “Energy transfer characteristics of the hydrogen peroxide induced Ce3+-Ce4+ mixture,” Spectrochim. Acta A Mol. Biomol. Spectrosc. 56(9), 1795–1800 (2000). [CrossRef] [PubMed]
19. E. Danielson, M. Devenney, D. M. Giaquinta, J. H. Golden, R. C. Haushalter, E. W. McFarland, D. M. Poojary, C. M. Reaves, W. H. Weinberg, and X. D. Wu, “A Rare-Earth Phosphor Containing One-Dimensional Chains Identified Through Combinatorial Methods,” Science 279(5352), 837–839 (1998). [CrossRef] [PubMed]
20. M. Balestrieri, S. Colis, M. Gallart, G. Schmerber, M. Ziegler, P. Gilliot, and A. Dinia, “Photoluminescence properties of rare earth (Nd, Yb, Sm, Pr)-doped CeO2 pellets prepared by solid-state reaction,” J. Mater. Chem. C Mater. Opt. Electron. Devices 3(27), 7014–7021 (2015). [CrossRef]
21. S. Gomez-Salces, J. A. Barreda-Argueso, R. Valiente, and F. Rodriguez, “A study of Ce3+ to Mn2+ energy transfer in high transmission glasses using time-resolved spectroscopy,” J. Mater. Chem. C Mater. Opt. Electron. Devices 4(38), 9021–9026 (2016). [CrossRef]
22. Y. Zhou, D. Yin, S. Zheng, and X. Xu, “Energy transfer and enhanced 1.53µm band signal gain in Er3+/Ce3+ codoped tellurite glass fiber,” J. Quant. Spectrosc. Radiat. Transf. 129, 1–7 (2013). [CrossRef]
23. J. Yang, L. Zhang, L. Wen, S. Dai, L. Hu, and Z. Jiang, “Comparative investigation on energy transfer mechanisms between Er3+ and Ce3+ (Eu3+, Tb3+) in tellurite glasses,” Chem. Phys. Lett. 384(4–6), 295–298 (2004). [CrossRef]
24. A. K. V. Raj, P. Prabhakar Rao, T. S. Sreena, and T. R. Aju Thara, “Influence of local structure on photoluminescence properties of Eu3+ doped CeO2 red phosphors through induced oxygen vacancies by contrasting rare earth substitutions,” Phys. Chem. Chem. Phys. 19(30), 20110–20120 (2017). [CrossRef] [PubMed]
25. B. M. Reddy, P. Bharali, P. Saikia, S.-E. Park, M. W. E. van den Berg, M. Muhler, and W. Grünert, “Structural Characterization and Catalytic Activity of Nanosized CexM1-xO2 (M = Zr and Hf) Mixed Oxides,” J. Phys. Chem. C 112(31), 11729–11737 (2008). [CrossRef]
26. Y. Guo, M. Li, Y. Tian, R. Xu, L. Hu, and J. Zhang, “Enhanced 2.7 μm emission and energy transfer mechanism of Nd3+/Er3+ co-doped sodium tellurite glasses,” J. Appl. Phys. 110(1), 013512 (2011). [CrossRef]
27. T. Sasikala, L. R. Moorthy, K. Pavani, and T. Chengaiah, “Spectroscopic properties of Er3+ and Ce3+ co-doped tellurite glasses,” J. Alloys Compd. 542, 271–275 (2012). [CrossRef]
28. H. Chen, Y. H. Liu, Y. F. Zhou, and Z. H. Jiang, “Spectroscopic properties of Er3+-doped tellurite glass for 1.55μm optical amplifier,” J. Alloys Compd. 397(1-2), 286–290 (2005). [CrossRef]
29. K. Linganna, G. L. Agawane, and J. H. Choi, “Longer lifetime of Er3+/Yb3+ co-doped fluorophosphate glasses for optical amplifier applications,” J. Non-Cryst. Solids 471(Supplement C), 65–71 (2017). [CrossRef]
30. H. Kim, M. Kim, and S.-H. Byeon, “Ce4+/Ce3+ redox-controlled luminescence ‘off/on’ switching of highly oriented Ce(OH)2Cl and Tb-doped Ce(OH)2Cl films,” J. Mater. Chem. C Mater. Opt. Electron. Devices 5(2), 444–451 (2017). [CrossRef]
31. P. Bera and C. Anandan, “XRD and XPS studies of room temperature spontaneous interfacial reaction of CeO2 thin films on Si and Si3N4 substrates,” RSC Advances 4(108), 62935–62939 (2014). [CrossRef]
32. C. Anandan and P. Bera, “XPS studies on the interaction of CeO2 with silicon in magnetron sputtered CeO2 thin films on Si and Si3N4 substrates,” Appl. Surf. Sci. 283(Supplement C), 297–303 (2013). [CrossRef]
33. F. Piccinelli, A. Speghini, G. Mariotto, L. Bovo, and M. Bettinelli, “Visible luminescence of lanthanide ions in Ca3Sc2Si3O12 and Ca3Y2Si3O12,” J. Rare Earths 27(4), 555–559 (2009). [CrossRef]
34. F. Bensalem, F. Bozon-Verduraz, M. Delamar, and G. Bugli, “Preparation and characterization of highly dispersed silica-supported ceria,” Appl. Catal. A Gen. 121(1), 81–93 (1995). [CrossRef]
35. S. Sarkar, M. Chatti, V. N. K. B. Adusumalli, and V. Mahalingam, “Highly Selective and Sensitive Detection of Cu2+ Ions Using Ce(III)/Tb(III)-Doped SrF2 Nanocrystals as Fluorescent Probe,” ACS Appl. Mater. Interfaces 7(46), 25702–25708 (2015). [CrossRef] [PubMed]
36. A. M. Ebrahim and T. J. Bandosz, “Ce(III) Doped Zr-Based MOFs as Excellent NO2 Adsorbents at Ambient Conditions,” ACS Appl. Mater. Interfaces 5(21), 10565–10573 (2013). [CrossRef] [PubMed]
37. S. Gómez-Salces, J. A. Barreda-Argüeso, R. Valiente, and F. Rodríguez, “Solarization-induced redox reactions in doubly Ce3+/Mn2+-doped highly transmission glasses studied by optical absorption and photoluminescence,” Sol. Energy Mater. Sol. Cells 157, 42–47 (2016). [CrossRef]
38. B. M. Weckhuysen and R. A. Schoonheydt, “Recent progress in diffuse reflectance spectroscopy of supported metal oxide catalysts,” Catal. Today 49(4), 441–451 (1999). [CrossRef]
39. G. Phaomei, R. S. Ningthoujam, W. R. Singh, R. S. Loitongbam, N. S. Singh, A. Rath, R. R. Juluri, and R. K. Vatsa, “Luminescence switching behavior through redox reaction in Ce3+ co-doped LaPO4:Tb3+ nanorods: Re-dispersible and polymer film,” Dalton Trans. 40(43), 11571–11580 (2011). [CrossRef] [PubMed]
