β-In 2 S 3 and β-In 2 S 3 :Co 2+ single crystals were grown by the chemical transport reaction method using In 2 S 3 , S, and ZnS as starting materials and (ZnCl 2 + 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 β-In 2 S 3 and β-In 2 S 3 :Co 2+ , respectively. The direct optical energy band gaps were found to be 2.639 eV and 2.175 eV for β-In 2 S 3 and β-In 2 S 3 :Co 2+ , respectively. Impurity optical absorption peaks were observed for the β-In 2 S 3 :Co 2+ single crystal. These impurity absorption peaks were assigned, based on the crystal field theory, to the electron transitions between the energy levels of the Co 2+ ion sited in T d symmetry.

CuAl 2 S 4 single crystals were grown with the constituent elements copper, aluminium and sulphur (purity 6N) as the starting material by the chemical transport reaction method using iodine as a transport agent. Layer-type colourless transparent single crystals were obtained, and the crystal structure of the single crystals was found to be cubic with the lattice constant a = 9.954 Å. The energy bandgap of the CuAl 2 S 4 single crystal was revealed to be direct bandgap, and the optical energy gap was found to be 4.10 eV at 10 K.

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