EPR studies of Gd3+ ions in lithium tetra boro-tellurite and lithium lead tetra boro-tellurite glasses

Glass systems of composition 85 Li2B4O7+(15−x) TeO2+x Gd2O3 (x=0, 1, 2, 3, 4 and 5 mol%) and 80 Li2B4O7+10 PbO+8 TeO2+2 Gd2O3 have been studied by using electron paramagnetic resonance (EPR). The EPR spectra indicate Gd3+ ions located at three types of sites randomly distributed in the host glass. The spectra exhibits three broad EPR signals at g≈2.0, g≈2.8 and g≈5.4 are attributed to Gd3+ ions located at sites with weak, intermediate and strong cubic symmetry fields respectively. In principle these sites may be of network forming and network modifying type. Ionic radius considerations suggest that gadolinium ions cannot substitute the much smaller boron ions and thus only the network modifier site is acceptable. The effect of gadolinium content as well as temperature 123-433 K on resonance signals have been investigated. The number of spins (N) participating in resonance and its paramagnetic susceptibility (χ) for g≈5.4 resonance line have been calculated as a function of Gd content and temperature. It is observed that N and χ increase with x. A linear relationship was established between log N and 1/T and the activation energy was calculated from the graph. From the graph the Curie constant (C) and Curie temperature (θ) have been evaluated. The temperature dependence of inverse magnetic susceptibility (1/χ) displays Curie-Weiss type of magnetic behaviour. The theoretical values of optical basicity (Λth) of the glasses have also been evaluated.