Eu²⁺ Doping Concentration-Induced Site-Selective Occupation and Photoluminescence Tuning in KSrScSi₂O₇:Eu²⁺ Phosphor

Regulation of Eu²⁺ dopants in different cation sites of solid-state materials is of great significance for designing multicolor phosphors for light-emitting diodes (LEDs). Herein, we report the selective occupation of Eu²⁺ for multiple cationic sites in KSrScSi₂O₇, and the tunable photoluminescence from blue to cyan is realized through Eu²⁺ doping concentration-dependent crystal-site engineering. Eu²⁺ preferably occupies the K and Sr sites in KSrScSi₂O₇ at a low doping concentration, resulting in a 440 nm blue emission. As the Eu²⁺ concentration increases, a new Eu²⁺ substitution pathway is triggered, that is, Eu²⁺ enters the Sc site, leading to the red-shifted emission spectra from 440 to 485 nm. The doping mechanism and photoluminescence properties are corroborated by structural analysis, optical spectroscopy study, and density functional theory calculations. The optical properties of the as-fabricated white LEDs are studied, which demonstrates that these phosphors can be applied to full-spectrum phosphor-converted LEDs. This study provides a new design strategy to guide the development of multicolor Eu²⁺-doped oxide phosphors for lighting applications.