Abstract: A series of CaWO₄∶Eu³⁺,Bi³⁺ red phosphors were successfully synthesized by high temperature solid-state reaction. The crystal structure, microstructure, optical property, energy transfer mode, fluorescence lifetime, and thermal stability of samples were characterized by X-ray diffraction, scanning electron microscope and fluorescence spectrophotometer, etc. The results show that when the doping concentrations of Eu³⁺and Bi³⁺ are 7% and 2% (mole fraction), respectively, the red luminescence (615 nm) is the strongest. Theoretical calculations show that the size of this fluorescent powder particle is around 50.27 nm. This is consistent with the observation results of the electron microscope. The main mode of energy transfer is the interaction between electric dipoles and electric quadrupoles. The fluorescence lifetime of CaWO₄∶7%Eu³⁺,xBi³⁺ (x=0~6%) series phosphors were measured, and their fluorescence lifetimes were basically the same, all around 0.56 ms. By comparing the spectra of CaWO₄∶7%Eu³⁺,2%Bi³⁺ phosphors at different temperatures, and the corresponding chromaticity coordinates were calculated. It was found that the overall chromaticity coordinates shift to the left, and the luminescence intensity becomes weaker as the temperature increases, but overall, the thermal stability is good. The good thermal stability and bright red emission indicate that this fluorescent powder can be used as a potential commercial red fluorescent powder.

Key words: CaWO₄, Eu³⁺ doping, Bi³⁺ doping, high temperature solid-state reaction, phosphor, sensitizer, fluorescence lifetime, thermal stability