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Abstract
Lu3Al5O12: Ce3+ (LuAG: Ce3+) phosphor ceramics (PCs) with high quantum efficiency and excellent thermal stability are incredibly promising color converters for high-power white light emitting diodes (LEDs)/ laser diodes (LDs) lighting. However, the greenish emission of LuAG:Ce3+ PCs does not allow to reach white light emission upon pumping by a blue LED/ LD without an additional red luminescent material. In this work, a series of (Ce0.003Lu0.997)3(MgxAl1−2xSix)5O12 (LCMASG) (x = 0–0.15) PCs were fabricated by solid state reaction method. Impressively, the as-prepared PCs exhibited a distinct red-shift (513→538nm) and a 17% increase of the color index (CRI) of high-power white LED(58.4→70.4). Particularly, Ce: Lu(Mg, Al)2(Si, Al)3O12 PC with 15 at.% substitution concentration showed only 8% luminescent intensity loss at 150 °C and high internal quantum efficiency (IQE) of 82%, exhibiting desirable optical thermal stability. By combining with a 460 nm blue chip or a 455 nm laser source, white LED/LD devices based on the LCMASG PCs in a remote excitation mode were constructed. The optimized luminous efficiency of Ce: Lu(Mg, Al)2(Si, Al)3O12 PC with 15 at.% Mg2+/Si4+ doping up to 176.4 lm/W was obtained as the power density of the blue laser increased to 6.52 W/mm2. Also, a 4053K CCT of the warm white light emission was realized. Therefore, this work proves that the LCMASG PCs are promising to serve as color converters for high power LEDs/LDs lighting in the future.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Currently, white light emitting diode (WLEDs) have been recognized for their long life time, high luminous efficiency and eco-friendliness [1–4]. In addition to being used as lighting source, it has entered several new applications, including LCD, backlights for portable electronic products, automotive headlights and plant cultivation, etc [5,6]. However, the blue LEDs have a serious problem of an “efficiency drop” at high input power density (> 3 W cm−2) [7,8], which limits their application in high power lighting. In contrast, a laser diode (LD) has a peak efficiency of 25 kW cm−2, making it become promising generation of high brightness lighting [9–13]. Meanwhile, the greater input power density for LD excitation means there will be plenty of heat accumulated during the light conversion process, which puts forward new requirements on the thermal conductivity of fluorescent materials [14–17].
To obtain the LD white lighting sources, many researchers have used the combination of yellow-green light emitted by Ce3+ with the remaining blue light from a LD. However, as current commercial packaging materials for phosphors, the organic resin with low thermal conductivity (0.1−0.4 W m−1 K−1) make it easy to age and turn yellow under high temperature for a long time, resulting in color temperature and color coordinate drift of device [9]. Therefore, as a phosphor conversion material, there are still some problems ought to be solved, and new phosphor conversion materials with high thermal conductivity need to be explored. Thus, YAG: Ce crystal [13,18–20], YAG: Ce phosphor in glass [21–25] and YAG: Ce phosphor ceramics (PCs) [9,26–29] as alternative materials are applied. Among them, YAG: Ce PCs have more notable advantage originating from their excellent luminescence properties, flexible ion doping and better thermal conductivity (about 14 W m−1 K−1) than resin-encapsulated phosphors [9,10,30–33]. Conversely, the deficiency of red component inherently limits its applications in high-quality white light. Up to now, the main methods to make up the red component include adding red phosphor [17,34], rare earth co-doping (Pr3+, Eu3+, etc.) [12,35], transition metal ion co-doping (Mn2+, etc.) [36–40] and crystal field regulation [41–44]. Relevant investigations using the above strategies are summarized in Table S1 of the Electronic supplementary information (ESI). As an effective strategy, Mg2+-Si4+ doping into YAG: Ce to redshift and broaden emission spectrum has been studied for obtaining a higher color rendering index (CRI > 60) and lower correlated color temperature (CCT < 5000 K) [9,45–47]. In 2018, for the first time, Du et al. reported the fabrication of Y3MgxAl5−2xSixO12: Ce (YAMSG: Ce) transparent ceramics, wide range spectrum regulation from 533 nm to 598 nm was accomplished [41]. However, in view of the poor thermal performance (∼60%@150°C) [9] and internal quantum efficiency (IQE) (∼50%) [41], YAMSG: Ce isn’t the best choice for high power LD lighting.
Generally, compared to YAG: Ce, LuAG: Ce has excellent thermal stability, higher luminescence intensity [44,48] and quantum efficiency [49]. Therefore, LuAG: Ce is considered as a promising phosphor conversion material to alleviate the adverse effects of thermal accumulation during high-power LD lighting [50,51]. Based on the strategy of crystal field regulation, previous reported spectral regulations mainly focused on the peak position of the emission spectra and FWHM value in phosphor material. However, in order to further improve the luminescence performance of ceramics excited by high power density laser lighting, not only the peak position and FWHM parameters need to be considered, but also the quantum efficiency, luminescence efficiency and thermal stability should be paid more attention. As an excellent converter system, Ce : LuAG phosphor ceramic was often designed to achieve higher CRI and lower CCT by co-doping Mg2+/Si4+ pairs in LuAG host, thanks to the fact that the spectral red shift can be realized by modifying crystal field environment in LuAG: Ce PCs [7,42–45,47,52–54]. Unfortunately, the impurity phases were often observed simultaneously with a large amount of Mg2+-Si4+ doping, which seriously decreased the thermal stability and luminous efficiency in high-power LD lighting [14,47,54]. In addition, the massive red shift of the emission spectrum results in the spectral gap of the cyan region, which greatly restricts the improvement of the CRI [46]. In previous studies, the large amount of Mg2+ ions doping often leads to the multi-lattice occupation (Lu3+, Al3+), doping Mg2+/Si4+ pairs to directly replace Al3+/Al3+ pairs in LuAG: Ce PCs and their luminous performance under LD excitation has been rarely investigated until now.
In this work, pure garnet phase (Ce0.003Lu0.997)3(MgxAll−2xSix)5O12 (LCMASG) (x = 0–0.15) PCs with high luminous efficiency and excellent thermal stability were fabricated via the solid-state reaction method. By the Mg2+-Si4+ pair substitution for the Al3+-Al3+ pair in octahedral and tetrahedral coordination of Lu3Al5O12:Ce3+ respectively, the strengthening of [CeO8] distortion and Stokes shift increased, generating the emission spectrum shifts from green to yellow. The effects of co-doping of Mg2+/Si4+ on the crystal structure, spectral performance and temperature-dependent of LCMASG were investigated systemically. Additionally, the remote encapsulation mode was used to construct LCMASG PCs-based white LED/LD devices, and their luminescence performances were verified. This work proves that LCMASG PCs are excellent candidates as phosphor conversion materials in high-power white LEDs/LDs lighting.
2. Experimental procedures
2.1. Ceramic fabrication
(Ce0.003Lu0.997)3(MgxAll−2xSix)5O12 (LCMxASxG) (x = 0, 0.05, 0.075, 0.1, 0.125, 0.15) was synthesized by the high-temperature solid-state reaction method using Lu2O3 (99.99%), Al2O3 (99.999%), MgO (99.99%), SiO2 (99.99%) as starting materials without other sintering aids. And organic polyethyleneimine (PEI) was used as dispersing agent. After stoichiometrically weighed, the raw materials were mixed by ball milling for 15 h in ethanol, dried in the oven at 55 °C for 12 h. And the dried powders were pulverized and sieved 3 times using 100 mesh, calcined at 800°C for 6 h in muffle furnace, dry-pressed into a stainless steel mold of Ф22 mm wafers and cold isostatically pressed (CIPed) under 200 MPa for 200s. Then the samples were sintered at 1700 °C and for 8 h in a vacuum furnace with 10−5 Torr. After being annealed at 1450 °C for 10 h in air to remove oxygen vacancies, the ceramics were polished to 1.0 mm on both sides. For the sake of simplicity, we denoted these samples as LCAG, LCM05ASG, LCM08ASG, LCM10ASG, LCM13ASG and LCM15ASG, respectively. The detailed composition design in this study is listed in Table 1. Also, the flowchart of whole preparation process is shown in Fig. 1.
Table 1. Ingredients of the LCMASG CPs
2.2. Characterization
An X-ray diffractometer was used to identify the phase composition of ceramics (XRD, Model D5005, Siemens). Morphologies of all samples were characterized by a scanning electron microscopy (SEM, JSM-6510, JEOL, Tokyo, Japan). Elemental mapping of the samples was obtained using an energy dispersive X-ray spectroscopy (EDS, Inca X-Max, Oxford Instruments, Oxford, England). An UV-Vis-NIR spectrophotometer (Lambda 950, Perkin Elmer, USA) was used to test the transmission spectra of the polished PCs. Photoluminescence (PL), photoluminescence excitation (PLE), fluorescence decay and temperature-dependent luminescence spectra were recorded using a fluorescence spectrophotometer (FLS 920, Edinburgh, UK), and the adopted excitation source was a 450 W Xenon lamp. A quantum efficiency spectrometer was used for the quantum efficiency test of PCs (C11347-11, Hamamatsu, Japan). The chromaticity parameters of the samples were measured using an integrating sphere (R98, Everfine, Hangzhou, China) excited by a 460 nm blue LED chip as well as a 455 nm laser source. Temperature distribution of samples was recorded using an infrared thermal imaging instrument (Fotric 226 s, Fotric, America).
3. Results and discussion
Figure 2(a) gives the measured XRD patterns of LCMxASxG (x= 0, 0.05, 0.075, 0.10, 0.125 and 0.15) with different Mg2+-Si4+-doping concentration. With the increase of Mg2+-Si4+ substitution concentration, there were no miscellaneous peaks or phases, and all diffraction peaks were corresponded to LuAG standard peaks. This indicated that the substitution of Mg2+-Si4+ for octahedral and tetrahedral Al3+ could still be achieved even if the substitution concentration of Mg2+-Si4+ were 15 at.%, and the prepared LCMASG PCs still presented pure LuAG phase. The principal diffraction peak (420) was gradually shifted to lower diffraction angles, in agreement with increasing Mg2+-Si4+ doping concentrations and the induced increase in cell parameters [43]. In fact, the radius of Si4+ (R = 0.4 Å) is smaller than that of Al3+ (R= 0.53 Å) in AlO4, though the radius of Mg2+ (R= 0.86 Å) is larger than that of Al3+ (R= 0.675 Å) in AlO6, and the difference of ion radius is within the range that can replace Al3+(less than 15%) [49,55]. Therefore, when Mg2+-Si4+ ion pairs were co-substituted at the same concentrations, the lattice parameters increased with the replacement of Mg2+-Si4+. As an embodiment of LCMASG garnet, the ceramic crystallizes in a body-centered cubic structure with three-dimensional framework formed by edge- and vertex- shared (Lu/Ce)O8 dodecahedra (Wyck. 24c), (Al1/Mg)O6 octahedra (Wyck. 16a), and Al2/SiO4 tetrahedra (Wyck. 24d), as shown in Fig. 2(b).
Fig. 2. (a) Measured X-ray patterns of LCMxASxG: Ce ceramics and enlarged view of local angle around 34°, (b) Crystal structure of Lu3Al5O12 (left) and the coordinated environments of the (Lu/Ce)O8 dodecahedron, the (Al/Mg)O6 octahedron, and the (Al/Si)O4 tetrahedron(right).
The SEM images of the thermal etched surface and fracture surface of the LCM15ASG ceramic are displayed in Fig. 3. Along with a few residual pores at grain boundaries, the uniform grains and clear grain boundaries are exhibited in Fig. 3(a). The average grain sizes of LCM15ASG were 3.27 µm. When applied to high power lighting, these residual pores could be used as light scattering centers to improve the efficiency of ceramics. Besides, the fracture surface of LCM15ASG is shown in Fig. 3(b). The fracture mode of the ceramic was intergranular fracture modes. In addition, the density of ceramics has also been tested through the Archimedes method. With the increase of Mg2+-Si4+ doping concentration, the density of ceramics gradually increased from 5.5259 g/ cm3 to 6.6439 g/ cm3. In fact, a small amount of Mg2+-Si4+ ions could act as sintering aids to promote the densification of ceramics. The EDS mapping images of the annealed LCMASG PCs with substitution concentration of 15 at.% are shown in Fig. 3(c)–3(i). It could be seen from Fig. 3(c) that the (Lu, Ce)/(Al, Mg, Si) ratio of the sample was close to the theoretical value of LuAG (3:5), Fig. 3(d)–3(i) also showed that Lu, Al, O, Ce, Mg and Si elements were distributed homogeneously, indicating that all Mg2+-Si4+ ions were solid soluted into the LuAG lattice.
Fig. 3. SEM of the surface (a) and the fracture surface of (b) LCM15ASG, (c)-(i) EDS mapping for the LCM15ASG.
In order to maintain the unity of variables, a relatively low temperature of 1700 °C was used for sintering, while the best sintering temperature of Ce3+: LuAG is up to 1800°C [22,56–58]. The lower temperature resulted in the lower transmittance of the ceramics. In-line transmission spectra of LCMASG PCs and their appearances are displayed in Fig. S1 (ESI). As phosphor materials, especially when applied to LD lighting, the lack of scattering centers will result in a “yellow-ring” problem, which has adverse effect on color uniformity and efficiency. Due to the large difference in refractive index between air and LuAG and no absorption of emission light by air, pores have often been considered as scattering centers [59]. Therefore, the presence of scattering centers, such as pores, can notably increase the emission intensity of ceramic phosphors compared to high transmittance.
Figure 4(a) and 4(b) show the PLE (λem = 530 nm) and PL (λex = 460 nm) spectra of LCMASG: Ce PCs with different Mg2+-Si4+ substitution concentrations under the excitation of 460 nm blue LED chip, respectively. In accordance with other reports, LuAG: Ce PCs without Mg2+-Si4+ substitution can emit green light at around 510 nm in the central band under the excitation of 460 nm blue light [58,60]. Obviously, the PLE spectra monitored at 530 nm exhibited a strong excitation band located at around 460 nm and a weak excitation band located at around 340 nm, attributing to the 4f→5d transitions of Ce3+ ion. With the increasing of Mg2+-Si4+ substitution concentration of Al3+ in AlO6 and AlO4, the PLE spectra showed a slight blue shift or remain unchanged. However, the PL spectrum of LCMASG PCs gradually redshifted under the excitation of 460 nm blue light [41]. The peak location redshifted from 513 nm to 538 nm with increasing Mg2+-Si4+ substitution concentration from 0 to 15 at.%. In fact, the distortion of [CeO8] was strengthened by Mg2+-Si4+ ions substitution, leading to the downward shift of 5d1 energy level. Meanwhile, it also led to the decrease of LuAG: Ce lattice structural rigidity. The influence of the two factors on the excitation spectrum could be basically offset, but being opposite for the emission spectrum [46,54,61]. Finally, the PLE and PL spectra of LCMASG: Ce PCs displayed an obviously opposite trend. Also, the peak intensity of PL spectrum is shown in Fig. S2 (ESI). All LCMASG PCs exhibited the asymmetric wide emission. Due to spin-orbit coupling, the energy levels of the Ce3+ ion in the 4f state split into two energy levels, 2F5/2 and 2F7/2. The PL spectrum composed of two peaks originated from the transitions of 5d1→ 2F7/2 and 5d1→ 2F5/2, finally presenting asymmetric broadband emission. Correspondingly, gaussian bands peaking of LCM15ASG PC were fitted at 18954 cm−1 (527 nm) and 17782cm−1 (562 nm) in Fig. 4(c).
Fig. 4. Normalized (a) PLE and (b) PL spectra of LCMxASxG: Ce ceramics with different Mg2+/Si4+ substitution concentrations (460 nm excitation), (c) gussian fitting for the PL spectra of LCM15ASG, (d) schematic energy-level diagram of Ce3+ in LCMASG, (e) the detailed peak positions and FWHM of Ce3+ emission, (f) IQE of LCMASG: Ce ceramics with different x values.
To investigate the relationship between Mg2+-Si4+ ions substitution and the electronic energy levels of Ce3+, the schematic energy-level diagram of Ce3+ is exhibited in Fig. 4(d). The emission wavelength of Ce3+ in LCMASG garnet depends on both the splitting of the 4f- 5d and the crystal field splitting of the energy levels in the 5d state. The structure of LuAG garnet in the solid solution replaced by Mg2+/ Si4+ is fixed, so the energy difference of 4f - 5d is basically unchanged. The reason for the spectral redshift is that the 5d1 orbital of the 5d energy level moves to the lower energy level [61–63]. For a simple point charge model, the crystal field splitting has been shown that the crystal field splitting varies as [63]
Figure 4(e) intuitively shows the detailed peak positions and FWHM of Ce3+ emission. With the increasing of Mg2+-Si4+ substitution concentration, the peak positions of Ce3+ ions were shifted from 512 nm to 538 nm, and the FWHM values modestly increased from 83 nm to 89 nm, indicating the electron-phonon coupling enhanced with the decreasing of the structure rigidity [46]. The variation in emission wavelength makes it easy to adjust the color characteristics of solid-state devices for different applications. Compared with the green emission of Ce3+: LuAG, the red shift of PL spectrum caused by the co-substitution of Al3+ by Mg2+ and Si4+ makes Ce3+: LuAG need less additional red light supplementation. In addition, the IQE of PCs are displayed in Fig. 4(f). The IQE values were decreased from 94.6% to 82% with the increase of Mg2+-Si4+ substitution concentration, substantially demonstrating the excellent luminescence performance.
The influence of Ce3+ on the decay curves in LCMASG PCs is shown in Fig. 5. The average decay time of the ceramic samples were 66.46, 63.13, 59.61, 57.71, 56.33 and 56.54 ns, respectively. The declined lifetimes of PCs with the increase of Mg2+-Si4+ substitution concentration should be attributed to the enhanced non-radiative relaxation due to the decreasing activation energies (ΔE).
Generally, the operation temperatures of LED chips could reach up to ∼150 °C. To evaluate the applicability of as-prepared PCs to high power lighting, the thermal stability of LCM15ASG PC was analyzed based on temperature-dependent PL spectra in Fig. 6(a) and 6(b). The emission intensity of LCM15ASG PC decreased with increasing temperature. To observe the changes of emission intensity and peak wavelength intuitively, Fig. 6(c) is displayed. As the temperature increased from 25 °C to 300 °C, the peak wavelength of LCMASG PCs was redshifted from 535 nm to 545 nm, and the FWHM still remained about 89 nm. The redshift in the temperature-dependent spectrum might be attributed to the thermally-induced dynamical tetragonal distortions of the CeO8 moieties with high vibrational frequencies, which led to an increase of the tetragonal crystal field splitting [64].
Fig. 6. (a) and (b) Temperature-dependent PL spectra of LCM15ASG PCs under 460 nm excitation in the temperature range of RT-300 °C, (c) Normalized temperature-dependent PL intensities and peak wavelength of prepared PCs, (d) The emission intensity and temperature Arrhenius fitting of LCM15ASG PC.
It is universally acknowledged that the deterioration of thermal stability with the increasing of Mg2+-Si4+ substitution concentration is inevitable, ascribing to the increasing of crystal field splitting and the decreasing of structural rigidity. The configuration coordination diagrams used to understand the thermally quenching phenomenon is displayed in Fig. S2 (ESI). Under thermally activation, the excited luminescence center was released through the intersection between the ground state and the excited state. Generally, the structural rigidity of the host is associated with R. The more rigid lattices tend to have a smaller R. The increasing Mg2+-Si4+ ion concentration resulted in the enlarged R, reducing the rigidity structure and the activation energy (ΔE). However, as the highest doping concentrations of PCs, the photoluminescence spectrum intensity of LCM15ASG ceramic decreased only 8% when the temperature reached 150 °C, exhibiting the satisfactory thermal stability. Arrhenius equation was used to calculate ΔE of LCM15ASG PC as follows [63,65,66]:
The remote excitation mode was used to construct the LCMASG PCs based white LED devices. Also, a white LD coupling a 455 nm laser emitting source with as-prepared PCs was constructed by the reflective mode. The electroluminescent spectra (EL) and lighting of the LCMASG PCs are exhibited in Fig. 7(a)–7(f), the LCMASG PCs excited by 460 nm blue chip under 350 mA driving current in the integrating sphere. Consistent with the spectral red shift phenomenon shown in the PL spectrum, it was obvious that the color of LCMASG PCs gradually changed from green to yellow upon Mg2+-Si4+ concentration increasing. Owing to the lower blue light transmittance of LuAG: Ce3+ PC, the utilization rate of blue light was much lower in LuAG: Ce3+ than that in LCMASG PCs. Hence, in the absence of Mg2+-Si4+ substitution, the blue light intensity of 460 nm was much higher than that of LCMASG PCs. Accordingly, the luminescence in the inset of Fig. 7 also changed from blue to green, and finally to white as the substitution concentration increased. Figure 7(g) shows the CCT and Ra of LCMASG PCs upon Mg2+-Si4+ concentration increasing. The CCT of LCMASG PCs decreased from 6471 to 4062, and the Ra increased from 58.4 to 70.4. It was also consistent with the spectral red shift reflected in the emission spectrum of LCMASG PCs. The obtained CIE coordinates (Fig. 7(h)) of white LEDs were changed from blue-green to yellow-orange, which was in accordance to the color hue of the LED devices (insert). The variation in emission wavelength made it easy to adjust the color characteristics of solid-state devices for different applications.
Fig. 7. Photographs of the lighting PC-based white LEDs and the corresponding EL spectra of (a) LCAG, (b) LCM05ASG, (c) LCM08ASG, (d) LCM10ASG, (e) LCM13ASG, (f) LCM15ASG, (g) the corresponding CRI and CCT values, (h) CIE color coordinates under 350 mA current excitation.
Figure 8 present the EL spectra, CIE coordinates and the schematic diagram of the white LD device based on LCMASG PCs operating at an incident power of 3.0 W. In Fig. 8(a), the obtained emission intensity of LCMASG PCs was gradually decreased with the Mg2+-Si4+ concentration increasing from 0 to 15 at.%. Accordingly, and the CIE coordinates were also located from the (0.3353, 0.5386) cyan region to (0.4056, 0.4929) yellow region. Keeping the position of the LD excitation source and the ceramic unchanged, the EL spectra of the LCM15ASG PC are displayed in the Fig. 8(c). The emission intensity of the LCM15ASG PC increased as the input power increases from 1.0 W to 2.0 W, and then decreased. Finally, the schematic diagram of LD devices based on LCMASG PCs is shown in Fig. 8(d).
Fig. 8. (a) EL spectra (insert: appearances of the PC based white LDs) and (b) CIE color coordinates of the constructed LD devices, (c) EL spectra of LCM15ASG PC based LD as a function of the input power, (d) schematic diagram of LD devices.
To further explore the luminescence performance of LCMASG ceramics under high power density excitation, Fig. 9 shows the changes of the luminous flux, the luminous efficiency, the CRI and CCT of the ceramics with increasing power density. The saturation threshold of LCM10ASG, LCM13ASG and LCM15ASG were 13.0, 9.8 and 6.5 W/mm2, respectively (Fig. 9(a)). Obviously, the saturation threshold decreased with the increase of Mg2+-Si4+ doping concentration, implying the loss of heat resistance. Among them, the maximum luminous flux of LCM15ASG PC reached 352.9 lm, while showing a high luminous efficiency of 176.4 lm/W (Fig. 9(b)). The variations of the CRI and CCT with the increasing power density are exhibited in Fig. 9(c) and 9(d). It could be seen that the obtained CRI and CCT changed in quite small range, proving excellent color stability.
Fig. 9. (a) Luminous flux, (b) luminous efficiency from blue laser light to white light, (c) CRI, (d) CCT of all PCs dependent on the excited power density.
As known, the heat generation of PCs crucially affects their working condition at high power. Therefore, the surface temperatures of LCMASG PCs excited by a 455 nm laser diode were recorded with infrared camera under the exciting power of 3.0 W in Fig. 10. Also, the recorded surface temperatures of PCs were labeled. The surface temperatures rose from 80.6 to 151.6 °C with the increasing of Mg2+-Si4+ concentration at an incident laser power of 3.0 W, mainly ascribing to decreasing IQE and Stokes shift [67]. Finally, the integrated results indicated that Ce: Lu(Mg, Al)2(Si, Al)3O12 PCs were favorable to the high power white LED/LD applications relying on their excellent spectral thermal stability and highly luminous efficiency. It also provided a new host material for warm white light lighting applications through further doping rare earth ions and transition metal ions.
4. Conclusion
In summary, a series of (Ce0.003Lu0.997)3(MgxAl1−2xSix)5O12 (x = 0–0.15) PCs have been synthesized using vacuum sintering technology and investigated by the construction of high power white LEDs/LDs. By substituting the Al3+/Al3+ pairs in octahedral and tetrahedral coordination with Mg2+/Si4+ pairs, the crystal field intensity of LuAG: Ce PC was adjusted to achieve the red shift of the spectrum(∼25 nm), thus improving the CRI of LuAG: Ce PC from 58.4 to 70.4 as phosphor conversion materials for white light illumination. Ce: Lu(Mg, Al)2(Si, Al)3O12 PC with 15 at.% substitution concentration showed high thermal stability(92%@ 150 °C) and high IQE= 82% was obtained. The LF of the optimized Lu(Mg, Al)2(Si, Al)3O12 PC with 15 at.% increased from 164.5 lm to 877.4 lm, as increasing the exciting power density from 3.26 W/mm2 to 6.52 W/ mm2, and the corresponding LE was as high as 176.4 lm/W. Also, a 4053 K CCT of the warm white light emission was realized. The surface temperature of PCs increased from 80.6 to 151.6 °C under 3.0 W LD excitation. Finally, this study hold promises for the realization of high-quality and high-power LCMASG PCs based white lighting devices.
Funding
National Key Research and Development Program of China (2021YFB3501700); National Natural Science Foundation of China (51902143, 61775088, 61971207, 61975070); Priority Academic Program Development of Jiangsu Higher Education Institutions (BE2019033); Natural Science Foundation of Jiangsu Province (BK20191467); Postgraduate Research & Practice Innovation Program of Jiangsu Province (SJCX21_1137); International Science and Technology Cooperation Program of Jiangsu Province (BZ2019063, BZ2020030, BZ2020045); Natural Science Foundation of the Jiangsu Higher Education Institutes of China (19KJB430018, 20KJA430003); Special Project for Technology Innovation of Xuzhou City (KC19250, KC20201, KC20244, KC21379); Open Project of State Key Laboratory of Advanced Materials and Electronic Components (FHR-JS-202011017).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
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