Tunable emission of single-phased NaY(WO₄)₂:Sm³⁺ phosphor based on energy transfer

A series of NaY(WO₄)₂:Sm³⁺ phosphors were prepared by high temperature solid state reaction. When excited by ultraviolet and blue light, their emission spectra cover entirely visible light region, due to intrinsic luminescence of WO₄^2- group as well as Sm³⁺ 4f-4f transitions. White light emission was obtained from NaY_0.99Sm_0.01(WO₄)₂ phosphor under radiation of 265 nm UV light, and intense yellow and red emission from ⁶H_{J(J=5/2, 7/2, 9/2)} transitions were observed when pumped Sm^{3+ 4}G_5/2 by 405 nm blue light. With incorporation of Sm³⁺ into NaY(WO₄)₂ host, higher-level emission from Sm³⁺ at 650 nm was generated by energy transfer from WO₄^2- to Sm³⁺ under excitation of 265 nm. The corresponding energy transfer mechanism was demonstrated to be a dipole-dipole interaction. In addition, tunable emission from blue to white and, finally, to red was realized by increasing Sm³⁺ doping concentration. The band gap of NaY(WO₄)₂ calculated from diffuse reflection spectra indicates a semiconducting character. All these results show that NaY_1−xSm_x(WO₄)₂ phosphor provides promising application for conversion of frequencies emitted by UV or blue LEDs.