Colorless SnO- and Sb2O3-containing borate and borosilicate glasses with small photoelastic and high refractive properties

We examined the relationship between optical properties and structures of 5s2-type cations such as Sn2+- and Sb3+-containing borate and borosilicate glass. Linear evolutions were observed for the compositional dependences of density, glass transition temperature, refractive index, and photoelastic constant in visible transparent oxide glasses. The structural information was provided using vibrational spectroscopy to elucidate polyhedral units of the borate and borosilicate systems. A weak ligand field around a Sn2+ close to tetrahedral borate unit, which is supported by applying density functional theory calculation, might lead to a blueshift of optical bandgap keeping small photoelastic constant and high refractive index.