Spectrally Tunable Dual-Phosphor Ceramics for Laser Lighting

Luminescent composite ceramics with two or more distinct phosphors are required to finely control the optical properties of laser-driven solid-state lighting, but they are hardly densified due to their different sintering temperature and chemical reactions between them. Then, highly dense and efficient dual-phosphor ceramics consisting of orange-emitting Ca-α-SiAlON:Eu and yellow-emitting YAG:Ce phosphors is successfully prepared by spark plasma sintering. Fine Ca-α-SiAlON:Eu powders and Al₂O₃-coated YAG:Ce (YAG:Ce@Al₂O₃) powders are used as raw materials, which enable to obtain dense Al₂O₃-Ca-α-SiAlON:Eu (Ceramic-Ca) and Al₂O₃-Ca-α-SiAlON:Eu-YAG:Ce@Al₂O₃ (Ceramic-Ca+Y@Al₂O₃) ceramics at 1480 °C. The chemical reaction between Ca-α-SiAlON:Eu and YAG:Ce can be hindered by using the Al₂O₃ surface coating, and the photoluminescence properties of both phosphors are thus remainedduring high-temperature sintering. The Ceramic-Ca+Y@Al₂O₃ show tunable spectra with emission maximum ranging from 541 to 601 nm, an external quantum efficiency of ≈42%, thermal conductivity of >17.6 W m⁻¹ K, maximal luminance saturation of 18.8 W mm⁻², excellent thermal and color stabilities. It demonstrates that the dual-phosphor ceramics containing equivalent Ca-α-SiAlON:Eu and YAG:Ce allow to create super-brightness laser lighting with an output luminous flux density of 782.5 lm mm⁻² and a color temperature of 2278 K. This work paves an avenue to fabricate multi-phosphor composite ceramics for color-temperature-tunable laser-driven white light.