EPR and optical absorption spectral studies of Cu2+ ions doped in alkali lead tetraborate glasses

Electron paramagnetic resonance and optical absorption spectra of Cu2+ ions in 90R2B4O7+(10-x) PbO + xCuO (where R=Li, Na and K; 0.25 x 1.5mol% of CuO) glasses have been studied. EPR spectra of all glasses show resonance peaks characteristic of Cu2+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been evaluated. The values of spin-Hamiltonian parameters indicate that Cu2+ ions in alkali lead tetraborate glasses have octahedral coordination with a strong tetragonal distortion. The number of spins participating in resonance is measured as a function of temperature and the activation energy is calculated. The paramagnetic susceptibility is also calculated from the EPR data at various temperatures. From the plot of temperature versus 1/chi, the Curie constant and the Curie temperature values have been evaluated. The optical absorption spectra of all the glass samples show two bands. One broad band at low-energy side is assigned to 2B1g- > 2B2g transition of Cu2+ ion and the intense band at high-energy side is assigned to charge transfer band. By correlating EPR and optical absorption data, the molecular orbital coefficients have been evaluated.