Ce:LuAG transparent ceramics for high-brightness solid-state lighting: Fabrication and effect of Ce concentration

Abstract

Compared to phosphor and phosphor in glass, phosphor ceramics have higher thermal properties, and are less prone to thermal quenching. (Ce,Lu)3Al5O12 (Ce:LuAG) has better thermal stability than most of the phosphors, such as (Ce,Y)3Al5O12 (Ce:YAG). However, the high melting point of Lu3Al5O12 (LuAG; up to 2010 °C) presents a great challenge in producing transparent ceramics (TCs), so a series of Ce:LuAG nanopowders with high sintering activity were prepared by the co-precipitation method and then used as initial materials to obtain x at.% Ce:LuAG (x = 0.05, 0.1, 0.2, 0.3, 0.35, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7) TCs by vacuum sintering at 1775 °C for 10 h. Moreover, the luminous properties of typical Ce-doped LuAG phosphors were systematically investigated using excitation by light-emitting diodes or laser diodes (LEDs/LDs). The emission intensity of 0.4 at.% Ce doped sample is the highest among all TCs with Ce amount ranging from 0.05 to 0.7 at.% at room temperature. The photoluminescence intensity of 0.4 at.% Ce:LuAG only decreases by 12.5% from 25 to 225 °C. The 0.4 at.% Ce:LuAG based on 0.8 W LEDs and 1.1 W LDs has the optimum luminous flux of 71.5 and 113.7 lm and the luminous efficiency of 89.3 and 101.4 lm∙W−1, respectively. As Ce concentration increases, a decrease in the luminescence saturation threshold of TCs is observed with a blue laser power density of 2.5–36.9 W∙mm−2. A high-flux yellow-green light of 1166.9 lm is obtained from 0.1 at.% Ce:LuAG when excited with a high-power LD with an energy density of 36.9 W∙mm−2. This work explored the best Ce doping level in Ce:LuAG TCs, as well as the luminescence saturation threshold in remote laser lighting applications.