Site-selective spectroscopy of Eu3+ doped lead germanate glasses

A series of lead germanate glasses of molar compositions (x - 1)PbO-(100- x )GeO2-1Eu(2)O(3) with x = 30, 40 and 50 were prepared and studied by laser- induced fluorescence line narrowing (FLN) techniques. The energies of the S tark levels of the 'Fj an F, multiplets were obtained from experimental FLN spectra and a crystal field (CF) analysis was carried out for each excitat ion energy. The dependence of the CF Bk, parameters on the excitation energ y is qualitatively similar to the behaviour observed for Eu3+ in other oxid e glasses. The CF calculated ratios B-22/B-20) and B-44/B-40 agree reasonab ly well with the trend predicted by the Brecher and Riseberg geometric mode l. The CF strength parameter S decreases with increasing lead content in th e glass host. This behaviour is explained on the basis of the tendency of l ead 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 ge rmanium. (C) 2001 Elsevier Science B.V. All rights reserved.