Correlations between EPR and optical properties: Diborovanadate glasses in a highly modified regime

Abstract Glasses with composition x V 2 O 5 - 10PbO – (90 − x) NaBO 2 with 10 ≤ x ≤ 30 were prepared by a novel, energy-efficient and economical microwave method. The Electron Paramagnetic Resonance (EPR) spectra of all the glasses investigated exhibited a well-defined hyperfine structure, from which the spin Hamiltonian parameters of the VO 2 + ion, dipolar hyperfine coupling parameters, and the fermi-contact interaction term (K) have been calculated. The values of g-tensor reveal the existence of the VO 2 + ion in octahedral coordination with a tetragonally compressed site. The variations seen in P, K, Pβ 2 K and PK/γ with V 2 O 5 content indicate the s character of the magnetic spin of vanadium which arises due to the partial unpairing of s-electrons. Also, a decrease in K with V 2 O 5 mol% suggests a strong V O interaction, makes the bond length (V O) in the vanadyl group shorter and distorts the vanadyl group from O h to C 4V . The EPR and UV–Vis parameters are analyzed on the basis of structural motifs formed due to the network modification. The molecular orbital coefficients α 2 and γ 2 have been calculated. The ratio, 1 − γ 2 1 − α 2 increases with increasing V 2 O 5 mol%, suggesting that the σ-bonding between the V atom and the equatorial ligand is weakening. IR studies reveal the presence of [BO 3/2 ] 0 , [BO 4/2 ] − and [B 2 V 2 O 9 ] 2 − structural groups in the glass matrix.