Energy transfer from Bi3+ to Eu3+ triggers exceptional long-wavelength excitation band in ZnWO4:Bi3+, Eu3+ phosphors
Abstract
Color-tunable phosphors of ZnWO4:x mol% Bi3+, 3 mol% Eu3+ (x = 0.5, 1, 2, 3, 4, 5) were prepared through a precipitation method and their luminescence properties were investigated as a function of Bi3+ concentration. The most intense 616 nm emission indicates that Eu3+ occupies the Zn2+ sites without inversion symmetry. The spectral overlap between the emission band of Bi3+ and the excitation band of Eu3+ supports the energy transfer from Bi3+ to Eu3+, which has been demonstrated to be of a resonant type via a dipole–dipole mechanism. Energy transfer from Bi3+ to Eu3+ triggers a long-wavelength excitation band at 340 nm originating from the Bi3+ 1S0 → 3P1 transition, which makes the phosphors fit for long-wavelength radiation. The decay curves of Bi3+ and Eu3+ emission were measured to understand the energy transfer processes. Interestingly, the critical concentration of Bi3+ for Eu3+ 616 nm emission in ZnWO4:Bi3+, Eu3+ was greatly increased by 400 times compared with that for Bi3+ 560 nm emission in ZnWO4:Bi3+. Color-tunable emission in ZnWO4:Bi3+, Eu3+ phosphors can be obtained by the modulation of the excitation wavelength and the ratio of Bi3+ and Eu3+. Our work provides a novel approach to develop phosphors which can be excited effectively under long-wavelength radiation.