The purpose of this paper was to identify the defect nature of the centers responsible for the blue photoluminescence of cadmium thiogallate. The authors investigated the photoluminescence spectra of undoped CdGa//2S//4 crystals as well as of crystals containing excess cadmium acquired during growth or irradiated with high-energy neon ions. Such ion irradiation was used to increase the number of intrinsic defects. As expected, implantation of these ions resulted in partial disordering of the cation sublattice, and, consequently, in the appearance of a blue photoluminescence band in the spectrum.