Infrared transmitting bismuth germanate glasses containing zinc oxide

Abstract

Some new infrared transmitting bismuth-germanate glasses containing zinc oxide have been investigated. These glasses contain up to 20 mol% ZnO, the GeO₂ content varies from 60 to 80 mol%, the remainder being made up of Bi₂O₃. The partial substitution of ZnO for GeO₂ is found to slightly increase the 50% cut-off wavelengths. The molar volumes of the glasses decrease with the increase in ZnO content. The hardness of glasses, in general, tends to increase with the addition of ZnO. All the glasses studied are resistant to water and the resistance towards 3N HCl is found to vary depending on the ZnO and Bi₂O₃ content of the glasses. The results are explained on the basis of glass structure taking into consideration the effects of nonbridging oxygen ions (dependent on Bi₂O₃ and ZnO concentration), the change in polarizability of the oxygen ions as well as switching of some of the GeO₄ tetrahedra to GcO₆ octahedra after ZnO addition, and formation of ZnO₄ tetrahedra, especially in glasses of high ZnO content.