Site-selective spectroscopy of Eu3+ doped lead germanate glasses

A series of lead germanate glasses of molar compositions (x−1)PbO–(100−x)GeO2–1Eu2O3 with x=30, 40 and 50 were prepared and studied by laser-induced fluorescence line narrowing (FLN) techniques. The energies of the Stark levels of the 7F1 and 7F2 multiplets were obtained from experimental FLN spectra and a crystal field (CF) analysis was carried out for each excitation energy. The dependence of the CF Bkq parameters on the excitation energy is qualitatively similar to the behaviour observed for Eu3+ in other oxide glasses. The CF calculated ratios B22/B20 and B44/B40 agree reasonably well with the trend predicted by the Brecher and Riseberg geometric model. The CF strength parameter S decreases with increasing lead content in the glass host. This behaviour is explained on the basis of the tendency of lead to form strongly directional Pb–O bonds. On the basis of the present CF analysis, we find no evidence of changes of the local structure at the Eu3+ sites on increasing the amount of lead and also of 6-fold co-ordinated germanium.