[ [Math Processing Error] ] single crystals were grown by the Bridgman-Stockbarger method. The single crystals crystallized into a defect chalcopyrite structure. The optical energy band gap of the single crystals was investigated in the temperature range 11-300K. The optical energy band gap of the [Math Processing Error] single crystal was smaller than that of the [Math Processing Error] single crystal. The temperature dependence of the optical energy band gap of the single crystals was well fitted by the Varshni equqtion. The impurity optical absorption spectrum of the [Math Processing Error] single crystal was measured in the wavelength region 300-2300 m at 80 K. Impurity absorption peaks in the spectrum were analyzed within the framework of the crystal field theory and were attributed to the electron transitions between the energy levels of [Math Processing Error] sited in the Td symmetry point.