Fe3+ ions in alkali lead tetraborate glasses-an electron paramagnetic resonance and optical study

Glass systems of composition 90R2B4O7 + 9PbO + 1Fe2O3 (R = Li, Na and K) and 90Li2B4O7 + (10 − x)PbO + xFe2O3 (x = 0.5, 1, 3, 4, 5, 7 and 9 mol%) have been investigated by means of electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra exhibit three resonance signals at g ≈ 6.0, 4.2 and 2.0. The resonances at g ≈ 6.0 and 4.2 are attributed to Fe3+ ions in rhombic and axial symmetry sites, respectively. The g ≈ 2.0 resonance signal is due to two or more Fe3+ ions coupled together with dipolar interaction. The EPR spectra of 1 mol% of Fe2O3 doped in lithium lead tetraborate glass samples have been studied at different temperatures (123-433 K). The intensity of g ≈ 4.2 resonance signal decreases and the intensity of g ≈ 2.0 resonance signal increases with the increase of temperature. The line widths are found to be independent of temperature. The EPR spectra exhibit a marked concentration dependence on iron content. A decrease in intensity for the resonance signal at g ≈ 4.2 with increase in iron content for more than 4 mol% has been observed in lithium lead tetraborate glass samples and this has been attributed to the formation of Fe3+ ion clusters in the glass samples. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/χ versus T graph. The optical absorption spectrum of Fe3+ ions in lithium lead tetraborate glasses exhibits three bands characteristic of Fe3+ ions in an octahedral symmetry. The crystal field parameter Dq and the Racah interelectronic repulsion parameters B and C have also been evaluated. The value of interelectronic repulsion parameter B (825 cm−1) obtained in the present work suggests that the bonding is moderately covalent.