EPR and Optical absorption spectral investigations of VO2+ ion in M2O-TeO2-As2O3-B2O3-V2O5 (where M = Li and K) glasses.

Alkali tellurite glasses based on the compositions xLi₂O-(30−x)TeO₂-10As₂O₃-58B₂O₃-2V₂O₅ and xK₂O-(30−x)TeO₂-10As₂O₃-58B₂O₃-2V₂O₅ (where x = 5, 10, 15, 20, and 25 mol%) have been prepared using the melt quenching method, and their EPR, optical, and structural properties were investigated as a function of alkali ion concentration. The X-ray diffraction analyses showed that Li₂O and K₂O- doped tellurite boro-arsenate glasses had a completely amorphous structure. The electron paramagnetic resonance spectra of VO²⁺ ions in these glasses have been recorded in the X band (9.14 GHz) at room temperature. The spin Hamiltonian parameters, dipolar hyperfine coupling parameter, and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) due to V⁴⁺ ions which exist as VO²⁺ ions, in octahedral coordination with a tetragonal compression in the present glasses. The optical absorption spectra reveal the characteristic spectrum in the visible region for the V₂O₅ doped prepared samples show three visible absorption peaks at ~ 462nm (²B_2g → ²A_1g), ~ 581 nm (²B_2g → ²B_1g), and ~ 798 nm (²B_2g → ²E_g) in order of increasing wavelength, respectively. The optical band gap energies (E_opt) and Urbach energy (ΔE) have been determined from their ultraviolet edges. The theoretical values of optical basicity (Λ_Th) of these glasses have also been evaluated. The density N (V⁴⁺ ion concentrations) for spins and paramagnetic susceptibility participating in resonance can be estimated. Structural studies were made by recording FTIR absorption spectra. [ABSTRACT FROM AUTHOR]