The exitonic spectra of catodolumination of CdS(O) single crystals (the information depth 0.3-125 µm) have been investigated. It has been determined that the solid CdS(O) solution is stable in the volume, since the crystal lattice provides compensates the deformations of isoelectric impurity OS. Near the surface (up to 0.5μm) the solid CdS(O) solution may lose oxygen with the CdO, or SO formation. The wavelength of the simulated emission from the CdS(O) crystals is determined by [OS] in the volume CdS(O) in accordance with the analysis data.