EPR and optical absorption studies on Fe3+ ions in alkali borotellurite glasses

Electron paramagnetic resonance and optical absorption spectra of Fe 3+ ions in 85M 2 B 4 O 7 . (15-x)TeO 2 , xFe 2 O 3 [(M=Li, Na or K); 0.5≤x≤10 mol%] glass systems have been studied. The EPR spectra of all glasses exhibit three resonance signals at g=2.0, g=4.2 and g=6.4. EPR spectra of 3 mol% Fe 2 O 3 doped lithium borotellurite glass system were studied at various temperatures. The intensity of the resonance signals decreases with increase in temperature whereas linewidths are found to be independent of temperature. 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 3 mol% has been observed and this has been attributed to the formation of clusters in the glass samples. The paramagnetic susceptibility was calculated from the EPR data at various temperatures and the Curie constant was calculated from the 1/X versus T graph. The optical absorption spectrum exhibits five bands characteristic of Fe 3+ ions in a distorted octahedral symmetry. From the observed band positions, the crystal field parameter, Dq. and the Racah interelectronic repulsion parameters, B and C, have been evaluated. The optical band gap energy was found to decrease with increase in iron content which indicates that the nature of the glasses become more semiconducting with increase of iron content.