Optical and spectroscopic properties of germanotellurite glasses

In this work, new glass compositions in the TeO2–GeO2–Nb2O5–K2O system have been prepared and studied. The germanotellurite glasses were prepared by melt-quenching and their density, refractive index and characteristic temperatures have been determined. The structure of these glasses has been studied by infrared and Raman spectroscopies.The progressive replacement of TeO2 by GeO2 led to an increase of the glass transition and crystallisation temperatures of the glasses and a simultaneous decrease of their density and refractive index. Typical density and refractive index values of these glasses ranged from 4.98 to 3.85 g cm− 3 and 2.08 to 1.79, respectively, with increasing GeO2 content. The infrared spectra are dominated by a band ~ 640 cm− 1 in the tellurite glass and ~ 800 cm− 1 in the germanate glass. The Raman spectra of the germanotellurite glasses present an intense boson peak between ~ 34 and 47 cm− 1, together with high frequency peaks at ~ 670 cm− 1 and ~ 470 cm− 1 for high tellurite and high germanate glass compositions, respectively. The vibrational spectra of these germanotellurite glasses indicate that the glass network consists basically of TeO4 and [TeO3]/[TeO3 + 1] units, mixed with GeO4 and NbO6 polyhedra.

Research Highlights
► Germanotellurite glasses in the TeO2GeO2Nb2O5K2O system have been prepared and studied.
► GeO2 increased characteristic temperatures and decreased density and refractive index.
► Glass structure consists of TeO4, [TeO3]/[TeO3+1], GeO4 and NbO6 units.
► Tellurite and germanate units do not mix and TeO2-rich and GeO2- rich regions seem to occur.