Tunable photoluminescence in Ba_1-xSr_xSi₃O₄N₂: Eu²⁺/ Ce³⁺, Li⁺ solid solution phosphors induced by linear structural evolution

A series of oxynitride phosphors, Ba_1-xSr_xSi₃O₄N₂: Eu²⁺/ Ce³⁺, Li⁺ (0 ≤ x ≤ 0.5) have been synthesized through a solid state reaction method at a high temperature. The influence of Sr²⁺-doping on the structure and photoluminescence properties of Ba_1-xSr_xSi₃O₄N₂: Eu²⁺/ Ce³⁺, Li⁺ was studied systemically. All of the samples were found to retain their hexagonal crystal structures with the linear lattice shrinking upon the increase of Sr²⁺ concentration, indicating that Ba²⁺ is substituted by Sr²⁺ to form the intermediate solid-solution compositions of Ba_1-xSr_xSi₃O₄N₂. It is noteworthy that red shifts of about 30 and 7 nm in the emission spectra of Eu²⁺ and Ce³⁺-activated samples were observed, respectively, through the Sr substitution at Ba sites from 0 to 0.5, originating from the increment of crystal field strength and Stokes shift. The thermal quenching stability, fluorescence decay behavior and CIE values were discussed and compared. Based on these results, the Ba_1-xSr_xSi₃O₄N₂: Eu²⁺ phosphors are considered to be potential candidate phosphors applicable to n-UV LED for solid-state lighting.