Luminescence and quantum efficiencies of Eu³⁺-doped vanadate garnets

Nondoped and 5.0 mol% Eu³⁺-doped vanadate garnets Ca ₅Mg₄(VO₄)₆, NaCa₂Mg ₂[VO₄]₃, KCa₂Mg₂[VO ₄]₃, and NaSr₂Mg₂[VO ₄]₃ were synthesized by solid-state reactions. The formation of single-phase compound with garnet structure is confirmed by X-ray diffraction. The photoluminescence (PL) and PL excitation (PLE) spectra are investigated together with color coordinates. The luminescence process is discussed on the charge-transfer transitions in [VO₄]^3- ions and the crystal structure. The PL quantum efficiencies (QE) are measured for nondoped and Eu³⁺-doped samples. The Eu³⁺-doped samples have higher QEs than the corresponding nondoped ones although the energy transfer occurs from [VO₄]^3- to Eu³⁺. Broad emission band due to [VO₄]^3- with intense sharp lines due to Eu³⁺, which gives white color, is observed in Eu ³⁺-doped NaCa₂Mg₂[VO₄]₃ and NaSr₂Mg₂[VO₄]₃ under excitation with UV light. These materials are suggested to be useful for lighting under the excitation with near-UV LED.