Effects of Bi³⁺ ions on luminescence properties of ZnWO₄:Eu³⁺, Sm³⁺, Bi³⁺ nanorods

To develop red emitting phosphors for white LEDs, a series of ZnWO₄:xEu³⁺, ySm³⁺, zBi³⁺ (x, y and z are values in mol%, x = 5; y = 0, 0.6; 0 ≤ z ≤ 11) phosphors were prepared by hydrothermal method, and their structures, characteristic photoluminescence properties and energy transfer mechanism were studied in detail. The causes for the morphological changes after doping Sm³⁺ and Bi³⁺ ions were also analyzed in our work. It could be determined that all the samples were pure monoclinic ZnWO₄. For Bi³⁺ doped ZnWO₄:Eu³⁺, the dominant emission band located at 617 nm (when λ_ex = 357 nm) was significantly enhanced by the efficient energy transfer (from Bi³⁺ to Eu³⁺). In addition, the experiment also found that Bi³⁺ doped ZnWO₄:Eu³⁺ had a stronger emission than ZnWO₄:Eu³⁺ (without Bi³⁺ sensitization) excited at 465 nm. This phenomenon appeared in ZnWO₄:Eu³⁺, Sm³⁺, Bi³⁺ as well. Thus, we suggest that the introduction of Bi³⁺ leads to structural distortion that affects the f–f transition of Eu³⁺ in ZnWO₄:RE³⁺. The obtained results clearly indicate the beneficial influence of introduction of Bi³⁺ ions on luminescence properties of Eu³⁺ in our work.