Structural and luminescence properties of Sr2VO4Cl and Sr5(VO4)3Cl: self-activated luminescence and unusual Eu3+ emission

Abstract

Novel self-activated vanadate phosphors, blue-emitting Sr₂VO₄Cl and green-emitting Sr₅(VO₄)₃Cl, were synthesized via the solid-state reaction route, and the relationship between the structure and luminescence properties was comparatively investigated. Self-activated luminescence originating from the VO₄³⁻ charge transfer (VCT) transition in relation to different V–O distances was verified in two vanadate phases with different crystal structures. Sr₂VO₄Cl showed a blue emission band from 375 to 600 nm with a peak at 424 nm, while Sr₅(VO₄)₃Cl exhibited a green emission band from 375 to 700 nm with a peak at 517 nm. With the introduction of Eu³⁺ to Sr₂VO₄Cl, both the VCT and Eu³⁺ emissions were found; however, the VCT emission was quenched in Sr₅(VO₄)₃Cl after Eu³⁺ doping. Sr₅(VO₄)₃Cl:Eu³⁺ only shows the characteristic red emission lines originating from Eu³⁺, while Sr₅(VO₄)₃Cl:Eu³⁺,Na⁺ shows typical emissions coming from the VCT transition and the Eu³⁺ ions. As a comparison, the emission intensity of Sr₂VO₄Cl:Eu³⁺,Na⁺ decreased compared to that of Sr₂VO₄Cl:Eu³⁺. The intrinsic luminescence mechanism is discussed based on the differences in the crystal structures and the measured lifetimes.