Structural Investigations on Sodium–Lead Borophosphate Glasses Doped with Vanadyl Ions

Electron paramagnetic resonance (EPR), optical absorption, and FT-IR spectra of vanadyl ions in the sodium–lead borophosphate (Na2O–PbO–B2O3–P2O5) (SLBP) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The spin Hamiltonian parameters g and A are found to be independent of the V2O5 content and temperature. The values of the spin Hamiltonian parameters indicate that the VO2+ ions in SLBP glasses are present in octahedral sites with tetragonal compression. The population difference between Zeeman levels (N) is calculated as a function of temperature for an SLBP glass sample containing 1.0 mol % VO2+ ions. From the EPR data, the paramagnetic susceptibility (χ) is calculated at different temperatures, and the Curie constant (C) is calculated from the 1/χ versus T graph. The optical absorption spectra of the glass samples show two absorption bands, and they are attributed to V3+ and V4+ ions. The optical band gap energy (E opt) and Urbach energy (ΔE) are calculated from their ultraviolet absorption edges. It is observed that, as the vanadium ion concentration increases, E opt decreases and ΔE increases. The study of the IR absorption spectrum depicts the presence of BO3, BO4, PO3, PO4, and VO5 structural units.