Spectroscopic properties of monolithic sol–gel glasses doped with lanthanide bipyridyl complexes

Lanthanide complexes [Ln(bpy)2]Cl3 (bpy=bipyridyl, 2,2′-bipyridine; Ln=Nd, Ho, Er) were incorporated via a sol–gel process into a silicate glass. Optical absorption spectra of the monolithic glass samples have been recorded. The data were interpreted using the Judd–Ofelt theory. It was found that heat treatment of the glass samples results in a marked increase of the intensity of the hypersensitive transitions, whereas the intensity of the other f–f transitions decreases slightly. These differences in spectral behaviour are mainly caused by the removal of water molecules out of the coordination sphere of the lanthanide ions and by the densification of the glass matrix.