Synthesis and luminescence properties of ZnGa2O4 spinel doped with Co2+ and Eu3+ ions

ZnGa2O4 nanopowders doped with Co2+ and Eu3+ ions, including dual doping, have been synthesized by citrate sol–gel method, and characterized by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Results show that ZnGa2O4 spinels were produced by calcining the gel above 500 °C, with the crystallite size of 16–30 nm in the temperature range of 500–900 °C. Co2+ ions are located at the tetrahedral sites of ZnGa2O4 spinel by replacing Zn2+, and Eu3+ ions are incorporated in the defect regions at the grain boundaries. The emission spectra of Eu-doped ZnGa2O4 nanopowders display an intense emission at 615 nm belonging to 5D0–7F2 transition of Eu3+ ions. With the introduction of Co into Eu-doped ZnGa2O4, the emission intensity at 615 nm decreases, while the luminescence at 680 nm due to tetrahedral Co2+ increases. The result indicates that the energy transfer occurred from Eu3+ to Co2+ ions. The energy transfer was also studied by the luminescence decay behavior. The emission of Co and Eu Co-doped ZnGa2O4 also changed with annealing temperature. The luminescence properties of the doped ZnGa2O4 nanopowders can be controlled by the variation of Co and Eu doping concentration and annealing temperature.