Elaboration of Ce:(Lu,Gd)3Al5O12–Al2O3 transparent nanoceramics through full glass crystallization for high-power white LED/LD lighting

Abstract

Transparent Ce:Lu₃Al₅O₁₂ (Ce:LuAG) phosphor ceramics have emerged as promising color conversion materials in high-power white lighting due to their relatively high quantum efficiency, high thermal stability and low thermal quenching. However, the shortage of red spectral composition and expensive price are preventing the application of Ce:LuAG phosphor ceramics in high-quality white lighting. In this work, (Lu,Gd)₃Al₅O₁₂–Al₂O₃ (LuGAG–Al₂O₃) ceramics with nanoscale grains, in which Gd³⁺ is selected to partially replace Lu³⁺, were prepared through full glass crystallization from a 72 mol% Al₂O₃–28 mol% (0.8Lu₂O₃–0.2Gd₂O₃) bulk glass. These ceramics are composed of nanoscale grains (less than 50 nm) with a fully dense biphasic three-dimensional network nanostructure and exhibit outstanding transparency (82.3%@780 nm) and excellent mechanical properties (hardness is 23.4 GPa). Compared with Ce:LuAG–Al₂O₃ transparent nanoceramics, the emission spectrum of transparent Ce:LuGAG–Al₂O₃ nanoceramics shows a substantial red shift (505 nm → 570 nm), which effectively supplements the lack of red light in Ce:LuAG ceramics. And the transparent Ce:LuGAG–Al₂O₃ nanoceramics exhibit a maximum quantum efficiency of 81.4% and excellent thermal stability (87.6%@423 K), indicating potential for high-power white lighting. When used in high-power LED and LD lighting, Ce:LuGAG–Al₂O₃ transparent nanoceramics achieve continuous adjustable changes from green light to orange-yellow light, and furthermore provide high quality warm white lighting with low color temperature (CCT), a high color rendering index (CRI), and excellent luminous efficiency (LE). Especially, integrated to blue-emitting InGaN chips (10 W), 0.8%Ce:LuGAG–Al₂O₃ transparent nanoceramics generate state-of-the-art performance regarding warm white lighting (4526 K, 73.5, and 143.98 lm W⁻¹). Under blue laser-diode excitation (5 W mm⁻²), the in situ generated Al₂O₃ second phase as the scattering center improves the light conversion efficiency and a maximum luminous efficiency of 240.04 lm W⁻¹ is achieved. Combining the facile and moderate elaboration process through full glass crystallization, the transparent Ce:LuGAG–Al₂O₃ nanoceramics reported in this paper are therefore regarded as promising candidates as color converters for high-power white LED/LD lighting.