Broadband NaK₂Li[Li₃SiO₄]₄:Ce Alkali Lithosilicate Blue Phosphors

Abstract

Phosphors with a rigid and symmetrical structure are urgently needed. The alkali lithosilicate family (A[Li₃SiO₄]) has been extensively studied with a narrow emission band due to its unique cuboid-coordinated environment and rigid structure. However, here we demonstrate for the first time Ce-doped NaK₂Li[Li₃SiO₄]₄ phosphors with a broad emission band, a high internal quantum efficiency (85.6%), and excellent thermal stability. Photoluminescence indicates the Ce's preference to occupy the Na⁺ site, leading to a strong blue color emission with peak maxima at 417 and 450 nm. Temperature- and pressure-dependent photoluminescence reveals thermal stability and a phase transition. Moreover, the X-ray absorption near-edge structure reveals the mixing of Ce³⁺ and Ce⁴⁺ in the materials; this result differs from that of Eu²⁺-doped A[Li₃SiO₄] phosphors. The charge compensation process is then proposed to explain this difference. This study not only provides insights into Ce-doped UCr₄C₄-type phosphors but also explains the charge compensation mechanism of the aliovalent doping process.