Luminescence properties and energy transfer of CdWO4:Sm3+,Bi3+,M+(M=Li, Na, K) phosphors for white LEDs

A series of Sm3+–Bi3+ co-doped CdWO4 phosphors with wolframite structure have been prepared via a high temperature solid state reaction process and their structural and luminescence properties were thoroughly investigated. The color-tunable emission from blue to yellow can be realized by WO6–Sm3+ or WO6–Bi3+–Sm3+ energy transfer. A new distinct excitation bands from the CdWO4:Sm3+,Bi3+ phosphors are clearly observed at about 361 nm which comes from the 1S0→3P1 transitions of Bi3+. The Fluorescent Resonance Energy Transfer between Bi3+ and Sm3+ were considered to be the primary mechanisms and it was proved from their crystal structure. Based on the results in this study, CdWO4:Sm3+,Bi3+,K+ sample is considered as an efficient phosphor with excellent color tunability for white UV-LEDs.