OPTICAL-ABSORPTION OF ZNGA2S4-NI2-CRYSTALS( AND ZNGA2MN2+ SINGLE)

Single crystals of ZnGa2S4:Mn2+ and ZnGa2S4:Ni2+ were grown by chemica l vapor deposition technique. The absorption spectra of these crystals were measured in the wavelength region of 400-3000 run at 298 K. The optical energy gap is found to be 3.25 eV for the ZnGa2S4, 3.21 eV for the ZnGa2S4:Mn2+ and 3.15 eV for the ZnGa2S4:Ni2+ crystals. Three abs orption peaks were observed at 2.30 eV, 2.55 eV and 2.66 eV for the Zn Ga2S4:Mn2+ and assigned as, 6A1 --> 4E, 6A1 --> 4T2 and 6A1 --> 4T1 tr ansitions of Mn2+ at Td crystal field. The absorption peaks of ZnGa2S4 :Ni2+ were observed at 0.54 eV, 1. 14 eV, 1.50 eV, 1.76 eV, 1.94 eV an d 2.25 eV. These absorption transitions were assigned as, GAMMA1 --> G AMMA3 + GAMMA4, GAMMA1 --> GAMMA5, GAMMA1 --> GAMMA3 + GAMMA4, GAMMA1 --> GAMMA5, GAMMA1 --> GAMMA4 and GAMMA1 --> GAMMA3, respectively usin g Td crystal field along with the 1st order spin-orbit coupling effect .