Photoluminescence and energy transfer of phosphor series Ba2-zSrzCaMo1-yWyO6:Eu,Li for white light UVLED applications

Abstract

Series double-perovskite-type phosphors Ba2-zSrzCa0.80Eu0.10Li0.10Mo1-yWyO6 were synthesized by solid state reactions. To understand photoluminescence properties and the energy transfer process in the phosphors well, Raman spectra were collected and the first-principle calculations on the band structures were conducted for some selected samples. The series phosphors present relatively effective excitation bands in near UV range (370–400 nm), which originates from the charge transfer state of MoO6, and perform orange-reddish luminescence (595 nm) arising from the 5D0→7F1 transition of Eu3+. In Mo-rich phosphors, the luminescence of Eu3+ is weak, because the energy transferred among MoO6 groups along (MoCa)O6 framework is concentration quenched and less energy transfers to Eu3+. WO6 groups introduced into the lattice act as energy obstacles to block the energy transfer among MoO6 groups, which results in that more energy is transferred from MoO6 to Eu3+. Sr-rich phosphors in the series Ba2-zSrzCa0.80Eu0.10Li0.10Mo0.10W0.90O6 have better luminescence than Ba-rich phosphors. Possibly because in the former, the links among MO6 (M = Mo, W and Ca) octahedra are distorted and the possibility of the energy transfer among MoO6 groups is reduced, which leads to more energy trapped by Eu3+. The phosphors may be suitable for applications in white light ultraviolet light-emitting-diodes.