Synthesis and optical properties of Co2+-doped ZnGa2O4 nanocrystals

Co2+-doped ZnGa2O4 nanocrystals were prepared via a citrate sol–gel method. The as-obtained ZnGa2O4 nanocrystals are the only crystalline phase with an average diameter of 15–30 nm in the temperature range of 500–700 °C. Ga2O3 was detected when the powder was heated over 800 °C. So we think that the suitable fired temperature for the preparation of ZnGa2O4 nanocrystals is 500–700 °C. The observed absorption and emission spectra of the nanocrystalline powders in the visible and near infrared regions are characteristic of tetrahedral Co2+ ions. The crystal field parameter Dq of 402 cm−1 and the Racah parameters B of 765 cm−1 and C of 3420 cm−1 were estimated for tetrahedral Co2+ ions in ZnGa2O4 nanocrystals.