Al2O3–YAG:Ce composite phosphor ceramic: a thermally robust and efficient color converter for solid state laser lighting

Abstract

Solid state laser lighting is a newly emerging technology that combines a blue laser diode (LD) with a yellow-emitting phosphor converter to generate high-brightness white light. Due to high flux irradiation as well as thermal attack from the incident laser, this technology draws a demanding requirement on the thermal performance of the color converter. In this work, we design a Al₂O₃–YAG:Ce phosphor ceramic with a unique composite structure, where yellow-emitting YAG:Ce particles are embedded in a non-luminescent Al₂O₃ matrix having high thermal conductivity. The large YAG:Ce particles (5–20 μm) show good crystallinity and a high external quantum efficiency of 76% (upon 460 nm excitation) while the fine Al₂O₃ grains (0.5–2 μm) contribute to the superior in-line transmittance of 55% at 800 nm by minimizing the birefringence related scattering. The phosphor ceramic exhibits a high thermal conductivity of 18.5 W m⁻¹ K⁻¹ and a remarkable improvement in thermal stability (only an 8% reduction at 200 °C). When irradiated under 445 nm blue laser diodes, the phosphor ceramic shows no luminescence saturation even under a high power density of 50 W mm⁻², validating its suitability for high-power solid state laser lighting.