Effect of [Ln³⁺–Si⁴⁺] (Ln = Y, La, Gd, Lu) Cosubstitution on the Structure and Luminescence Property of Sr₉Mg_1.5(PO₄)₇:Eu²⁺ Phosphor

Abstract

Four series of isostructural solid solution phosphors with the composition of Sr 8.95Àx Ln x Mg 1.5 (PO 4 ) 7Àx (SiO 4 ) x :0.05Eu 2þ (Ln ¼ Y, La, Gd, Lu; x ¼ 0À2) are synthesized. The influence of [Ln 3þ ÀSi 4þ ] (Ln ¼ Y, La, Gd, Lu) cosubstitution on the structure and luminescence properties of Sr 9 Mg 1.5 (PO 4 ) 7 :Eu 2þ phosphor is evaluated. Spectra analysis indicates that the valence state of Eu in Sr 9 Mg 1.5 (PO 4 ) 7 :Eu 2þ phosphor can be controlled from Eu 3þ to Eu 2þ by cosubstituting [Ln 3þ ÀSi 4þ ] for [Sr 2þ ÀP 5þ ], leading to an obvious enhancement of Eu 2þ emission. The mechanism of abnormal reduction of Eu 3þ ions in the lattice is discussed. In addition, a blueshift of Eu 2þ emission is observed with increasing the [Ln 3þ ÀSi 4þ ] content. These findings not only suggest that the as-prepared Sr 9Àx Ln x Mg 1.5 (PO 4 ) 7Àx (SiO 4 ) x :Eu 2þ phosphors are potential candidates for near-UV-based white light-emitting diodes (LEDs) but also offer a novel way for Eu valence control and spectral tuning in Eu-doped phosphors with multiple activator sites.