STRUCTURAL STUDIES IN LEAD FLUOROGERMANATE AND FLUOROSILICATE GLASSES

We report the results of structural studies by means of Eu3+ fluorescence line narrowing techniques in the binary systems PbF2-GeO2 and PbF2-SiO2. Several features characteristic of the europium fluorescence in lead glasses are put forward. The absence of selectively excited emission at room temperature demonstrates an unusually large homogeneous broadening of the electronic levels. A relative increase in the 5D0 --> F-7(1) (magnetic dipole) with respect to the 5D0 --> F-7(2) (electric dipole) transition is observed with time-resolved detection. This effect shows that accidental coincidences of 5D0 --> F-7(0) energies and F-7(1) splitting do occur between europium sites differing only by their 5D0 lifetimes and magnetic dipole: electric dipolar relative intensities. The general characteristics are interpreted with oxygen neighbours for Eu3+ rather than fluorine ions. The crystal field strength expressed as N(v) = [SIGMA(k,q) (B(q)k)2 X 4-pi/(2k + 1)]1/2 (limited to k = 2 parameters) is slightly higher in the germanate than in the silicate matrix.