Lowering operating temperatures in high-power laser-excited LuAG:Ce films by improving crystallinity and increasing Ce <sup>3+</sup> content
Huiying Hu, Bingguo Xue, Shaohong Liu, Limin Zhou, Hao Yang Cui, Manmen Liu, Haigang Dong, Li Chen, Ming Wen, Feng Liu, Li Song, Liang Zuo
Abstract
High operating temperatures generally degrade the luminous performance of color converters used in high-power, laser-driven white lighting systems. This study demonstrates that the operating temperature of LuAG:Ce films can be significantly reduced, particularly under high-power laser excitation near the saturation threshold. This improvement was achieved by enhancing the crystallinity and increasing the Ce<sup>3+</sup> content in LuAG:Ce films. LuAG:Ce films, approximately 22.17 μm in thickness, were deposited on sapphire substrates via spray pyrolysis techniques. The crystallinity was controlled by the annealing temperature, while the Ce<sup>3+</sup> content was regulated by the annealing atmosphere. Air-annealed films with a crystallinity of 87.4% exhibited a remarkable 95.6 °C decrease in operating temperature compared to those with a crystallinity of 75.5% under 18 W/mm<sup>2</sup> blue laser excitation. Additionally, the incorporation of a higher Ce<sup>3+</sup> content through CO-annealing led to a further reduction in operating temperature. By lowering the operating temperature, LuAG:Ce films on sapphire substrates exhibit enhanced luminous performance and thermal stability under prolonged high-power laser excitation, which could inspire the design and development of advanced color converters for laser lighting applications.