New insights into the microstructure of translucent CaAlSiN3:Eu2+ phosphor ceramics for solid-state laser lighting

Abstract

Newly emerged phosphor ceramics play key roles in high-brightness solid-state laser lighting technologies. Recently, we developed a translucent CaAlSiN₃:Eu²⁺ red-emitting ceramic, with high quantum efficiency (up to 60%) and thermal robustness (15% higher than the powders). In the current work, detailed structural analyses are carried out by advanced analytical techniques, such as TEM and EPMA, in tandem with the CL, to reveal the correlation between the optical properties and the microstructure, especially the contribution of the interface. It was found that the ceramics consist of many core–shell structured phosphor particles. The shell is coated by a highly crystallized Ca-α-Sialon thin layer to reduce the surface defects. Such core–shell particles are embedded in a non-luminescent matrix of nano-sized Ca-α-Sialon particles tightly surrounded by an amorphous phase, both of which have little influence on the light propagation. Thanks to the unique core–shell structure of phosphor particles and the tight interfaces in the matrix, the bulk CaAlSiN₃:Eu²⁺ ceramic shows record high performance under blue laser irradiation. The output luminous flux increases linearly as the incident power density increases from 20 to 150 W cm⁻² with a constant high luminous efficacy of 42.2 lm W⁻¹, demonstrating its promising application in solid-state laser lighting.