Cathodoluminescence properties of CuGaS2 crystals grown by the iodine transport method are described. Four emission peaks are observed at about 497. 5nm, 520nm, 550nm and near infrared (700_??_750nm) region at 110K for as grown crystals. The appearance of these peaks is affected by the annealing in various atmospheres such as S, Ga, Cu and the vacuum, and by the deviations from the stoichiometric composition of the raw materials. It is supposed that the emission observed near 520nm arises from the transition from donor to acceptor related to VGa or CUGa and the emission near 550nm arises from the transition from level related to Vs to level related to VGa. The origin of the emission observed at 497.5nm is still uncertain. A tentative energy band model is proposed to explain the transitions observed as the above emissions.
