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.