Vanadium structural role in binary fluoride borate glasses and effects of gamma irradiation

Three binary fluoroborate glasses from the systems LiF-B2O3, NaF-B2O3 and CaF2-B2O3 (50 mol% each) together with V2O5-doped derived samples from the same three systems were prepared. Collective optical, FTIR and ` spectral measurements were carried out before and after gamma irradiation (6 M rad dose). FTIR spectra of the studied glasses reveal mostly repetitive vibrational curves with limited variations. The IR spectra show condensed vibrations due to both triangular (BO3) and tetrahedral coordinated fluoro-borate groups (BO3F) in their distinct and characteristic wavenumbers similar to that obtained from Li2O-B2O3, Na2O-B2O3 and CaO-B2O3 glasses. Gamma irradiation causes limited increase of the UV absorption within the optical spectra of undoped glasses and the generation of an induced small curvature in the visible. This behavior is related to some photochemical effects and the formation of (BOHC) or (NBOHC) or even similar fluoride analogues. The V2O5-doped glasses show some shielding behavior towards gamma irradiation and the spectral curves remain almost unaffected. ESR spectra show distinct signals for the undoped glass correlated with trace ferric oxide impurity. The V2O5-doped glasses before irradiation reveal three small signals indicating that the vanadium ions exist in V5+ with no unpaired electron and the few percent of low valence (V3+, V4+) ions producing the identified small signals. Gamma irradiation decreases the intensities of the small signals due to lower valence vanadium ions but causes the splitting of the main signals for the undoped and V2O5 doped samples. The calculated N-4 values are correlated with both ability of V2O5 to promote more (BO4) or (BO3F) units and the variations are correlated with housing behavior of LiF and NaF as modifiers while CaF2 which can form some (CaF4) units.