The physicochemical, optical, and luminescent properties and structures of glasses of the Ga2S3-GeS2-Sb2S3:Pr system have been studied in a wide range of concentrations of the main components in order to reveal their correlation with the composition. According to the calculations using the Judd–Ofelt theory, glasses with a high content of Sb2S3should provide the highest luminescence efficiency of Pr3+ions. However, this result is leveled by enhancing the concentration quenching effect, followed by an increase of the Sb2S3content in the glasses. The introduction of Pr leads to a significant increase in the fraction of Sb-Sb, Sb-Ge, Ge-Ge bonds in glasses enriched with Sb2S3and GeS2. In the cases of the glasses enriched with Ga2S3, this effect was not observed, apparently because Ga promotes the formation of three-coordinated sulfur atoms.