Biphasic (Lu,Gd)₃Al₅O₁₂-based transparent nanoceramic color converters for high-power white LED/LD lighting

Ce doped Lu₃Al₅O₁₂ (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)₃Al₅O₁₂–Al₂O₃ (LuGAG–Al₂O₃) nanoceramics with different replacing contents of Gd³⁺ (10%–50%) were successfully elaborated via a glass-crystallization method. The obtained ceramics with full nanoscale grains are composed of the main LuGAG crystalline phase and secondary Al₂O₃ phase, exhibiting eminent transparency of 81.0%@780 nm. After doping by Ce³⁺, the Ce:LuGAG–Al₂O₃ nanoceramics show a significant red shift (510 nm→550 nm) and make up for the deficiency of red light component in the emission spectrum. The Ce:LuAG–Al₂O₃ nanoceramics with 20% Gd³⁺ show high internal quantum efficiency (81.5% in internal quantum efficiency (IQE), 96.7% of Ce:LuAG–Al₂O₃ nanoceramics) and good thermal stability (only 9% loss in IQE at 150 ℃). When combined with blue LED chips (10 W), 0.3%Ce:LuGAG–Al₂O₃ nanoceramics with 20% Gd³⁺ successfully realize the high-quality warm white LED lighting with a color coordinate of (0.3566, 0.435), a color temperature of 4347 K, CRI of 67.7, and a luminous efficiency of 175.8 lm·W⁻¹. When the transparent 0.3%Ce:LuGAG–Al₂O₃ nanoceramics are excited by blue laser (5 W·mm⁻²), the emission peak position redshifts from 517 to 570 nm, the emitted light exhibits a continuous change from green light to yellow light, and then to orange-yellow light, and the maximum luminous efficiency is up to 234.49 lm·W⁻¹ (20% Gd³⁺). Taking into account the high quantum efficiency, good thermal stability, and excellent and adjustable luminous properties, the transparent Ce:LuGAG–Al₂O₃ nanoceramics with different Gd³⁺ substitution contents in this paper are believed to be promising candidates for high-power white LED/LD lighting.