Transparent YAG:Ce ceramic with designed low light scattering for high-power blue LED and LD applications

Abstract

Yellow-emitting YAG:Ce transparent ceramic is recognized as an ideal color converter in high-power blue LEDs and LDs, but the absence of scattering centers in its microstructure leads to a low light extraction efficiency and poor light uniformity. Here, taking advantage of the scattering effect and the transparency of YAG:Ce ceramics, Ce-free YAG phase was used as a second component to form a composite with YAG:Ce phosphor. The sintered YAG:Ce-YAG ceramic possessed a high transparency of ∼63 % and a thermal conductivity of 8.9 Wm−1 K−1. Due to its beneficial thermal properties and high external quantum efficiency of 70.2 %, the YAG:Ce-YAG ceramic could be excited under a high blue-laser flux density of up to 9.60 W/mm2 and showed a luminous emittance of 1220 lm/mm2. Due to light scattering arising from the slightly different refractive indices of the two phases, the designed YAG:Ce-YAG ceramic showed better lighting effects than a single-phase transparent YAG:Ce ceramic.