In this paper, the bonding states between composition ions and changes in the optical properties of glass according to the amount of substitution of La₂O₃ in La₂O₃-CaF₂-Al₂O₃-SiO₂ glass (hereinafter referred to as LCAS glass system) were studied. By analyzing the molar volume, density, and number of chemical bonds per unit volume of LCAS glass, it was confirmed that the added La₂O₃ acted as a glass network modifier. As the amount of substitution of La₂O₃ increased, the numbers of non-bridging oxygen and electron polarization increased, thereby reducing the optical band gap of the glass. As a result, it was confirmed that semiconducting behavior was exhibited in the glass. The La₂O₃-CaF₂-Al₂O₃-SiO₂ glass prepared in this study had a light transmittance of 75% or more, and the optical band gap energy could be changed as a function of amount of La₂O₃ substitution. It is concluded that LCAS glass can be used in various optical device fields such as optical sensors and lasers by controlling the amount of La₂O₃ substitution

Keywords: La₂O₃, Modifier, Optical band gap, Oxy-fluoride glasses