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 xLi(2)O-(30-x)TeO2-10As(2)O(3)-58B(2)O(3)-2V(2)O(5) and xK(2)O-(30-x)TeO2-10As(2)O(3)-58B(2)O(3)-2V(2)O(5) (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 similar to 462nm (B-2(2g) -> (2)A(1g)), similar to 581 nm (B-2(2g) -> B-2(1g)), and similar to 798 nm (B-2(2g) -> E-2(g)) in order of increasing wavelength, respectively. The optical band gap energies (E-opt) and Urbach energy (Delta E) have been determined from their ultraviolet edges. The theoretical values of optical basicity (Lambda(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.