Thermally self-managing YAG:Ce–Al2O3 color converters enabling high-brightness laser-driven solid state lighting in a transmissive configuration

Abstract

Achieving super-high brightness laser-driven solid state lighting in a transmissive mode is significantly limited by the thermal robustness and light extraction efficiency of color converter materials. Therefore, it is a must to enhance the thermal conductivity and conversion efficiency of color converters by appropriate compositional design and microstructural tailoring. In this work, we propose thermally self-managing YAG:Ce–Al₂O₃ composite ceramic color converters that consist of luminescent YAG:Ce phosphor particles embedded in a thermally conductive Al₂O₃ matrix, which allows them to be combined with high-power blue laser diodes to create super-high brightness white laser-driven light without using any heat sink. The thermal conductivity of the ceramic color converters increases linearly from 10.2 to 32.5 W m⁻¹ K⁻¹ as the Al₂O₃ content varies from 0 to 90 wt%. Impressively, the composite ceramic with 60 wt% Al₂O₃ can withstand an incident laser power density of up to 20.1 W mm⁻². A high-brightness white laser-driven light is obtained with a luminance of 982 Mcd m⁻². Moreover, the secondary Al₂O₃ particles also act as scattering centers and enhance the light conversion efficiency. A maximum luminous efficacy of 157 lm W⁻¹ is achieved under 11.94 W mm⁻² blue laser excitation at an Al₂O₃ content of 24 wt%, increased by 27.3% compared to the Al₂O₃-free YAG:Ce ceramic. The as-designed YAG:Ce–Al₂O₃ phosphor ceramics thus validate their great suitability in high-power and high-brightness laser-driven solid-state lighting.