Synthesis and characterization of K2O-ZnO-GeO2-SiO2 optical glasses

Abstract

Germanosilicate glasses are essential in the manufacture of optical amplifiers, waveguides, and solid-state lasers. ZnO, with a wide direct band gap of 3.37 eV, has a broad range of applications in UV-shielding materials. To the best of our knowledge, no previous research adding ZnO into germanosilicate glasses has been reported. In this study, thirteen samples centered around a molar composition of 20K2O-20ZnO-40GeO2-20SiO2 were melted, and the composition-property relationships were investigated. The densities are in the range of 3.18–3.46 g/cm3 and the refractive index values (RI) are between 1.588 and 1.630, close to the RI of pure GeO2 (1.603). Density and RI values increase with GeO2 and SiO2 concentrations. The UV cut-off edge is between 313 and 320 nm, significantly higher than the 157 nm value in typical soda lime glass. Fragility (m) and glass transition temperature (Tg) were determined by fitting viscosity data with the MYEGA equation. The Tg from the MYEGA equation is in good agreement with Tg values from DSC. Thermal expansion coefficient of samples is in the range of 102.7 to 139.2 × 10−7/°C, mainly influenced by the amount of ZnO and K2O. We conclude that these samples have relatively high refractive index, high transparency, good glass forming ability, and good UV-shielding properties, making them suitable for lens applications.