$Fe^{3+}$ ions in alkali lead tetraborate glasses-an electron paramagnetic resonance and optical study

摘要

Glass systems of composition $90R_{2}B_{4}O_{7} + 9PbO + 1Fe_{2}O_{3}$ (R = Li, Na and K) and $90Li_{2}B_{4}O_{7} + (10-x)PbO + xFe_{2}O_{3}$ (x = 0.5, 1, 3, 4, 5, 7and 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 $Fe^{3+}$ ions in rhombic and axialsymmetry sites, respectively. The g=2.0 resonance signal is due to two or more $Fe^{3+}$ ions coupled together with dipolar interaction. The EPR spectra of 1 mol% of $Fe_{2}O_{3}$ 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. Adecrease 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 $Fe^{3+}$ ion clusters in the glass samples. The paramagnetic susceptibility (chi) is calculated from the EPR data at various temperatures and the Curie constant (C) has been evaluated from 1/chi versus T graph. The optical absorption spectrum of $Fe^{3+}$ ions in lithium lead tetraborate glasses exhibits three bands characteristic of $Fe^{3+}$ 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 ofinterelectronic repulsion parameter B (825 $cm^{-1}$ obtained in the present work suggests that the bonding is moderately covalent.