The monograph describes the technique of the synthesis of glasses and the method of the growth of erbium-doped single crystals. The photoluminescence spectra of Ag 0.05 Ga 0.05 Ge 0.95 S 2-Er 2 S 3 glasses and glasses from the Ga 2 S 3-La 2 S 3-Er 2 S 3 system have been investigated in the visible and near-infrared ranges. According to the energy transitions in the erbium ions, a radiation mechanism for conversion and up-conversion luminescence has been established. The role of structural ordering and the influence of defects on the radiation efficiency of Er 3+ ions have been investigated. The spectra of photoluminescence of (Ga 54.59 In 44.66 Er 0.75) 2 S 300 and (Ga 69.75 La 29.75 Er 0.5) 2 S 300 single crystals have been studied. The efficiency of the radiation of the amorphous and crystalline materials has been compared. Also, the temperature dependence of the integral intensity of the radiation of glasses and single crystals has been studied. It is established that in a limited temperature range, these materials can be used for the manufacture of non-contact optical thermosensors.