Optical properties of β-In2S3 and β-In2S3:Co2+ single crystals

beta -In2S3 and beta -In2S3:Co2+ single crystals were grown by the chemical transport reaction method using In2S3, S, and ZnS as starting materials and (ZnCl2 + I-2) as a transport agent. The single crystals crystallized into a tetragonal structure. The indirect optical energy band gaps of the single crystals at 298 K were found to be 2.240 eV and 1.814 eV for beta -In2S3 and beta -In2S3:Co2+, respectively. The direct optical energy band gaps were found to be 2.639 eV and 2.175 eV for beta -In2S3 and beta -In2S3:Co2+, respectively. Impurity optical absorption peaks were observed for the beta -In2S3:Co2+ single crystal. These impurity absorption peaks were assigned, based on the crystal field theory, to the electron transitions between the energy levels of the Co2+ ion sited in T alpha symmetry.