We have developed pure inorganic and hybrid organic-inorganic solids b
y sol-gel processing of silicon alkoxides. 'Dense' gels are obtained a
t room temperature, in any desired shape, including thin films, and we
are able to trap organic molecules or clusters. Gels can be polished
and exhibit optical transmission in the visible range similar to that
of high-temperature silica glasses. Concerning 'gel-molecule' and 'gel
-nanocrystal' composites, the diversity of the organofunctional alkoxi
de precursors allows us to modify the optical properties by changing t
he nature and the strength of chemical and electronic interactions bet
ween the optically active guest system and the solid host matrix.