A. Patra et al., SPECTROSCOPIC STUDY OF CERIUM-DOPED SILICA-GEL MONOLITHS AND THEIR DENSIFIED DERIVATIVES, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 9(1), 1997, pp. 65-69
Cerium is exploited as a probe cation for elucidating the structure of
an alkoxide-derived silica gel and its progressive evolution to a gla
ss network as a function of heat-treatment up to 1000 degrees C. At in
termediate temperatures, the host structure exhibits inhomogeneity due
to insufficient formation of siloxane bonds, which is reflected by at
least two different sites and co-ordination spheres (termed ''high''
and ''low'' water ligation) for cerium. This is proved by the response
of the gels heated up to 700 degrees C to rehydration. Further format
ion of Si-O-Si network (900 degrees C) leads to the destruction of the
''high water'' sites of cerium and progression towards a glassy struc
ture. It is, however, only after heat-treatment at 1000 degrees C that
a dense silica glass network, not responding to rehydration, is final
ly obtained with cerium ions embedded in it.