Wenlei Liu,Jianxing Shen,Qingle Pang,Tailin Wang,Xiujun Han
Cerium-doped yttrium aluminum garnet (YAG:Ce) based transparent ceramics have been widely used in fluorescent lighting as high-quality inorganic fluorescent conversion materials. This paper further explores the Mg 2+ -Si 4+ ions doped YAG:Ce transparent ceramics by combining the solid-phase reaction method with vacuum hot-pressure sintering and implementing protection measures against hot-pressure mold contamination, and also investigates the effect of different Mg 2+ -Si 4+ doping contents on the structure, transmittance and luminescence properties of the ceramics under hot-pressure sintering. In this work, pure-phase YMASG:Ce transparent fluorescent ceramics with a grain size of about 3-6 μm and clear and clean grain boundaries were obtained with an In-line transmittance of 67% at 800 nm. Under the excitation at 460 nm, the emission peak was red-shifted by 26 nm and the full width at half maxima (FWHM) was broadened with the increase of Mg 2+ -Si 4+ content, which shows that the Mg 2+ -Si 4+ ion pair effectively complements the absence of the red light component in the YAG:Ce emission spectrum. The optimized YMASG:Ce ceramics obtained high-quality warm white light with a low correlated color temperature (CCT) and a high color rendering index (CRI) under the excitation of the blue LED chip. This work proved the feasibility of vacuum hot-pressure sintering to prepare YMASG:Ce transparent fluorescent ceramics, and provided a new approach for studying YMASG:Ce-based ceramics, which was significant for the application of high-power visible laser illumination.
Huanyu Zhao,Jinsheng Li,Yan Jiang,Yao Lu,Lei Wang,Yi Xie,Wenlong Zhou,Yang Li,Xudong Sun
(Y,Ce) 3 Al 5 O 12 (YAG:Ce) ceramic is considered to be a suitable phosphor converter with a high quantum efficiency and excellent thermal stability for laser-driven lighting. However, the lack of red emission in the spectrum of YAG:Ce leads to the poor color quality of white light under excitation of laser diodes (LDs). Although current solutions were investigated to improve the color rendering index (CRI), they inevitably cause the decreased luminous efficacies (LE). How to balance the two luminous properties is still troubling researchers. In this study, a novel composite structure with large YAG:Ce grains surrounded by fine YAG:Cr grains was obtained by the two-stage hot-pressing process. The energy transfer between Ce 3+ and Cr 3+ was reduced because they were in different phases due to the structural design, thus improving the red emission while avoiding a sharp decline in the yellow emission. Moreover, there was no reaction and difference in thermal expansion coefficient between two phases due to the same matrix of YAG. Furthermore, the reflection loss in YAG:Cr‒YAG:Ce composite ceramic was reduced compared to layered-structure ceramics. Therefore, the maximal CRI reached 71.3 and the maximal LE was 255.8 lm/W, indicating an excellent application prospect in laser-driven lighting.
To achieve extra-high brightness laser lighting, the bottleneck of thermally-induced luminance saturation that phosphor materials (i.e., color converters) usually suffer from under high power density laser excitation must be broken. However, the mechanisms for thermal saturation are not fully understood yet. Here, thermal saturation of typical Ce3+-doped garnet phosphor ceramics was systematically investigated by considering the balance among heat generation, dissipation and resistance of color converters. With increasing Ce concentration (0.0167 → 0.433%), the thermal saturation threshold decreases due to more heat generation (i.e., 3.97 → 6.73 W at an incident laser power of 6.73 W). A tunable saturation threshold (2–49 W mm−2) was observed by a chemical substitution strategy because of the difference in the thermal resistance and heat generation. The sample thickness exerts a complex influence on the saturation threshold accompanied by increased heat generation and enhanced heat dissipation corroborated by a broader temperature distribution curve. Based on these investigations, a high-flux white light of 2347.9 lm is obtained with robust YAG:Ce ceramics irradiated with a high power density of 31.94 W mm−2. Moreover, a promising green color converter able to withstand a blue laser power density of 49 W mm−2 was discovered for laser displays with an output luminous flux of 3967.3 lm. This work provides a principle to design and/or select phosphor materials with high thermal saturation thresholds, thus accelerating the rapid development of laser-driven lighting and displays.
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