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SbSBr, BiSBr, SbSBr:Co and BiSBr:Co single crystals were grown by the Bridgman technique. The grown single crystals crystallize in an orthorhombic structure and have an indirect band structure. The temperature dependence of t h e optical energy gap for the single crystals shows anomalies at the firstand second-order phase transition points. Cobalt dopants are located at the T, symmetry point in the hostsinglecrystais asCoZ+ and Co3+ ions. impurityoptical absorption peaks due to the electron transitions between the energy levels of the C$+ and Co3+ ions are observed.

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The optical transitions due to the cobalt transition metal impurity centers with composition x in C d1-k Co x Ga 2 S 4 mixed crystals were investigated by optical absorption spectroscopy. The optical absorption spectra showed three crystal-field transitions between the ground state 4 A 2 ( 4 F) and the excited states 4 T 2 ( 4 F), 4 T 1 ( 4 F), and 4 T 1 ( 4 P) of substitutional Co 2+ ions that were similar for all the investigated compositions. The crystal-field parameter (Dq) and the Racah parameter (B) obtained from the observed absorption bands showed a composition dependence such that the Dq parameter increases; on the other hand, the B parameter decreases with increasing composition x, which implies that the Racah parameter (B) depends strongly on the host crystal. Also, the total splitting between the highest and the lowest states of the 4 T 1 ( 4 P) state split due to spin -orbit coupling showed a composition dependence varying from 1576 cm -1 to 1232 cm -1 with increasing x. The spin -orbit coupling parameter λ varied from 394 cm -1 to 308 cm -1 with composition x.