Thermal, Structure and Optical Characterization of a Niobium Phosphotellurite System

Phosphotellurite glasses are promising materials for nonlinear optical applications due to their high nonlinear refractive index (n₂) and third-order susceptibility (χ³), as well as their low characteristic temperatures and suitable optical properties. In this work, pseudo-binary (100-x)TeO₂-xNbP glasses were synthesized using niobium phosphate (NbP) concentrations ranging from 1 to 20 mol%. The samples exhibited different structural characeristics, resulting in ceramic, glass, and glass-ceramic phases. The addition of NbP increased the glass transition temperature (323 to 398 °C) and thermal stability against crystallization (ΔT from 46 to 120 °C). Raman spectroscopy revealed structural modifications in tellurium-based units, along with the formation of Nb–O and P–O bonds. The composition containing 10 mol% NbP showed the highest nonlinear refractive index and two-photon absorption values among the studied samples, indicating promising potential for advanced nonlinear optical device applications.