Biphasic (Lu,Gd) <sub>3</sub>Al <sub>5</sub>O <sub>12</sub>-based transparent nanoceramic color converters for high-power white LED/LD lighting
Jie Fu, Ying Zhang, Shaowei Feng, Mathieu Allix, Cécile Genevois, Emmanuel Véron, Zhibiao Ma, Wenlong Xu, Linghan Bai, Ruyu Fan, Yafeng Yang, Hui Wang, Jianqiang Li
Abstract
Ce dopped Lu<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (Ce:LuAG) transparent ceramics are considered as promising color converters for solid-state lighting because of their excellent luminous efficiency, high thermal quenching temperature and good thermal stability. However, Ce:LuAG ceramics mainly emit green light. The shortage of red light as well as the expensive price of Lu compounds are hindering their application for white lighting. In this work, transparent (Lu,Gd)<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>-Al<sub>2</sub>O<sub>3</sub> (LuGAG-Al<sub>2</sub>O<sub>3</sub>) nanoceramics with different replacing contents of Gd<sup>3+</sup> (10%-50%) were successfully elaborated via a glass-crystallization method. The obtained ceramics with full nanoscale grains are composed of main LuGAG crystalline phase and secondary Al<sub>2</sub>O<sub>3</sub> phase, exhibiting eminent transparency of 81.0%@780 nm. After doping by Ce<sup>3+</sup>, the Ce:LuGAG-Al<sub>2</sub>O<sub>3</sub> nanoceramics show a significant red shift (510 nm→550 nm) and makes up for the deficiency of red light component in the emission spectrum. The Ce:LuAG-Al<sub>2</sub>O<sub>3</sub> nanoceramics with 20% Gd<sup>3+</sup> show high internal quantum efficiency (81.5% in IQE, 96.7% of Ce:LuAG-Al<sub>2</sub>O<sub>3</sub> nanoceramics) and good thermal stability (only 9% loss in IQE at 150 ℃). When combined with blue LED chips (10 W), 0.3%Ce:LuGAG-Al<sub>2</sub>O<sub>3</sub> nanoceramics with 20% Gd<sup>3+</sup> successfully realize the high quality warm white LED lighting with a color coordinates of (0.3566, 0.435), a color temperature of 4347 K, a CRI of 67.7 and a luminous efficiency of 175.8 lm·W<sup>-1</sup>. When the transparent 0.3%Ce:LuGAG-Al<sub>2</sub>O<sub>3</sub> nanoceramics are excited by blue laser (5 W·mm<sup>-2</sup>), the emission peak position red shifts from 517 nm to 570 nm, the emitted light exhibits a continuous change from green to yellow light green light to orange-yellow light and the maximum luminous efficiency is up to 234.49 lm·W<sup>-1</sup> (20% Gd<sup>3+</sup>). Taking into account the high quantum efficiency, good thermal stability, excellent and adjustable luminous properties, the transparent Ce:LuGAG-Al<sub>2</sub>O<sub>3</sub> nanoceramics with different Gd<sup>3+</sup> substitution contents in this paper are believed to be promising candidates for high-power white LED/LD lighting.