Investigation of Excitation Modes in Al₂O₃-YAG Phosphor Ceramics for High-Power Laser-Driven Lighting

The performance of laser-driven white light can vary significantly depending on the excitation mode. To attain desirable application performance of color converters in laser lighting, the excitation mode must be selected carefully. In this work, to understand the effect of the excitation mode on the performance of color converters, a detailed study was conducted on the heat dispersion, luminescence, and color quality of Al₂O₃-YAG:Ce phosphor ceramics in both transmissive and reflective modes. The relationship between ceramic porosity and scattering performance has also been analyzed by studying the beam expansion ratio. The results demonstrate that the phosphor ceramics in reflective mode exhibit superior heat dissipation capabilities and can withstand higher power laser excitation compared to the transmissive mode, while the light uniformity is relatively poorer due to the specular reflection. Therefore, in situations where a uniform light is not necessary, reflective color converters are more suitable for achieving superior luminance and luminous efficacy. Finally, a laser-driven white light device with a luminous flux of 1206 lm, a luminous efficacy of 241.2 lm W⁻¹, and a CCT of 5749 K has been realized using Al₂O₃-YAG:Ce phosphor ceramic in reflective mode, which can be applied for automotive headlights.