Luminescent properties and energy transfer of Sm3+ doped Sr2CaMo1-xWxO6 as a potential phosphor for white LEDs

Abstract

A series of Sm3+ doped Sr2CaMo1-xWxO6 phosphors were synthesized through solid state reaction process and their luminescent properties have been investigated. They presented excitation bands in UV, near UV and blue regions, originating from charge transfer transitions within Mo(W)O6 or Sm3+ f–f transitions. Concentration quenching still occurs among MoO6 groups even when Mo concentration is very low, however, if there is no Mo content in Sr2CaMo1-xWxO6 phosphors, absorption in near UV region cannot happen. It was found there is a big difference between the calculated optical band gap of Sr2CaMo0.02W0.98O6: 2% Sm3+ and that of Sr2CaMo0.01W0.99O6: 2% Sm3+. Band structure and density of state of Sr2CaMo0.5W0.5O6 were examined to explore the origination of charge transfer transition. Site occupation of Sm3+ in host lattice was discussed based on Raman spectra and group theory analysis. There are two kinds of luminescence centers in Sm3+ doped Sr2CaMo1-xWxO6 (x > 0) phosphors. When 98% Mo were substituted by W, the excitation band at 350 nm by monitoring 608 nm emission in Sr2CaMo0.02W0.98O6: 2%Sm3+ is about 8.5 times stronger than that in Sr2CaMoO6: 2%Sm3+. Energy transfer process was also discussed considering the overlap between the emission spectrum of Mo(W)O6 groups and the absorption spectrum of Sm3+, as well as the atom arrays of Mo6+(W6+), O2− and Sm3+.