Effects of preparation parameters on the long lasting luminescence of ZnGa2o4

Using high temperature solid state reaction method, ZnO and Ga2O3 with high purity as raw materials, different ZnGa2O4 samples were prepared at different molar ratios of raw materials and different temperatures, After excitation of the ZnGa2O4 samples by 254 nm UV lamps, obvious long lasting luminescence was detected for the first time, which showed two new long lasting luminescence peaks at 505 nm and 690 nm, respectively. And the relative intensity of the two peaks was effected by the preparation conditions such as molar ratio of the two raw materials and the sintering temperature. Less ZnO or higher temperature will strengthen the relative intensity of the 505 nm peak, while more ZnO or lower temperature will strengthen the relative intensity of the 690 nm peak. The origin of the two peaks was discussed based on some corresponding documents, and the conclusion is that the 505 nm peak comes from the 2EA→4A2 transition of Ga3+ in a relatively distorted octahedral after some Zn2+ are substituted by Ga3+; and the 690 nm peak comes from the V0*→O2- transition after the singly charged ion oxygen vacancies appeare in the octahedral structure. The reasons why the preparing conditions can affect the relative peak intensity of the two peaks were also discussed. Less ZnO will cause Zn2+ vacancies in the structure and more Ga3+ will occupy the Zn2+ positions, then will form distorted octahedral, and then the transition from energy level 2EA to 4A2 of Ga3+ will cause the 505 nm peak to be dominant. On the other hand, too much ZnO will form oxygen vacancies, which will cause the 690 nm peak to be dominant. Higher temperature will cause more evaporation of ZnO and then relative less ZnO, and lower temperature will cause less evaporation of ZnO and then more oxygen vacancies. These conclusions are corresponding with the origin of the two peaks discussed before.