The origin of emission color of reduced and oxidized ZnGa2O4 phosphors

The Ga–O octahedral structure of the reduced and the oxidized ZnGa2O4 phosphors was investigated using Reitveld refinement. The correlation between the structural change and the changing emission color was studied. The emission peak shifts to shorter wavelength because of the more contribution of a variation of ligand charge than that of bond length to crystal field. The blueshift behavior of the reduced ZnGa2O4 was also observed in Ge4+-doped ZnGa2O4. In addition, Li+ ions doping in ZnGa2O4 generate extra oxygen ions, and Li+-doped ZnGa2O4 shows the same emission color as the oxidized ZnGa2O4.