Tunable emission of single-phased NaY(WO 4 ) 2 :Sm 3+ phosphor based on energy transfer

A series of NaY(WO 4 ) 2 :Sm 3+ 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 WO 4 2- group as well as Sm 3+ 4f-4f transitions. White light emission was obtained from NaY 0.99 Sm 0.01 (WO 4 ) 2 phosphor under radiation of 265 nm UV light, and intense yellow and red emission from 6 H 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 Sm 3+ into NaY(WO 4 ) 2 host, higher-level emission from Sm 3+ at 650 nm was generated by energy transfer from WO 4 2- to Sm 3+ 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 Sm 3+ doping concentration. The band gap of NaY(WO 4 ) 2 calculated from diffuse reflection spectra indicates a semiconducting character. All these results show that NaY 1−x Sm x (WO 4 ) 2 phosphor provides promising application for conversion of frequencies emitted by UV or blue LEDs.