Optical and Mössbauer spectroscopy of lithium tetraborate glass doped with iron oxide

The glass system with composition [80Li2B4O7+(20-x) ZnO + xFe2O3] where x = (0, 2, 4, 6, 8 mol. %), was prepared by traditional melt quenching method. The impact of iron ions on the structural and optical properties of the investigated samples was studied by a set of commentary techniques including density, infrared, optical absorption, electron spin resonance (ESR) and Mössbauer measurements. The obtained results indicate that both the measured density and calculated molar volume increase with Fe2O3 content. IR spectra revealed the characteristic absorption bands of BO3, and BO4 structural unites. The optical absorption spectra of the glass samples featured four bands which are characteristic of Fe3+ in tetrahedral (Td) symmetry. The ligand field strength (10Dq), Racah parameters (B and C) and nephelauxetic effect (h) were calculated. ESR spectra were consistent with the optical findings, showing a broad resonance signal at g ~2.1, sharp signal at g ~4.1 and tiny shoulder (kink) at g ~ 6.7. Mössbauer spectra show two phases of iron ions existing within the glass network, the first is related to Fe3+ ions in octahedral (Oh) sites with the isomer shift (0.675–0.553) mm s−1, the second is related to Fe3+ ions in Td sites with the isomer shift below 0.34 mm s−1.