Reactive spark plasma sintering of YAG–YAG:Ce composite phosphor ceramics for laser-driven lighting with high luminous efficacy

Abstract

Composite phosphor ceramics (CPCs) have found extensive applications in high-power, high-brightness LD lighting, primarily due to their superior thermal conductivity, stability and microstructural tailorability. However, the high sintering temperatures and refractive index mismatches of CPCs impose a significant impact on their luminous efficacy and practical application. To address these challenges, this study introduces a novel approach utilizing reactive spark plasma sintering of mesoporous Y₂O₃ and Al₂O₃ powders and YAG:Ce phosphors. This approach leverages the enhanced driving forces stemming from mesoporous structure collapse and phase transformation, enabling the rapid preparation of dense polycrystalline YAG–YAG:Ce CPCs at a significantly reduced sintering temperature of 1350 °C and a short holding time of 3 minutes. Owing to the minimal refractive index difference and designed differential grain sizes, the resultant CPC exhibits a high internal quantum efficiency of 83.8%, which approaches 95.6% of that observed in YAG:Ce phosphors. When subjected to irradiation by a 450 nm laser diode, the as-prepared CPC produces white light with a remarkable luminous efficacy of 202.13 lm W⁻¹ and a low correlated color temperature of 5298 K, highlighting the enhanced light conversion efficiency. Furthermore, the CPC presents a substantial enhancement in thermal stability, experiencing only a 6% luminescence loss at 200 °C, and could endure a high laser flux density of up to 6.68 W mm⁻². These results demonstrate that the optimized YAG–YAG:Ce CPCs are well suited for solid-state laser lighting, and contribute to the ongoing advancement of next-generation lighting technologies.