Laser-driven composite ceramic enabling superhigh-luminance white light

Abstract

Laser-remote activated phosphor (LARP) converted solid state lighting is now developing towards high power density and super-brightness, and phosphor ceramic converters with high efficiency, high thermal conductivity, acceptable transmittance and suitable spectra are thus required. Y₃Al₅O₁₂:Ce (YAG:Ce)-based ceramics are promising color converters to produce white light with a color temperature of 6000 K for vehicle headlamps, but the brightness and luminous efficiency are not well optimized. In this work, two series of Al₂O₃-YAG:Ce and Al₂O₃-(Gd,Y)AG:Ce transparent ceramics were fabricated by vacuum sintering, and their microstructure, thermal and optical properties were controlled by changing the Ce³⁺ or Al₂O₃ content as well the thickness of the ceramics. Both Al₂O₃Y_2.925Al₅O₁₂:Ce_0.0175 (AY0.0175) and Al₂O₃-(Gd_0.1Y_2.89)Al₅O₁₂:Ce_0.01 (AGY) ceramics containing 70% (in mass) Al₂O₃ show a luminance saturation threshold of 30.3 W/mm² and 38.4 W/mm², enabling to produce white light with a color temperature of 6000 K, luminous flux of 1928 lm and 3101 lm, luminous efficiency of 135.0 lm/W and 161.1 lm/W when pumped by blue laser diodes, respectively. This work provides a solution to finely control the composition, microstructure, and optical properties of transparent ceramics for super-high brightness laser-driven solid-state lighting.