Studies on hybrid organic/inorganic nanocomposite gels using photoluminescence techniques

Transparent nanocomposite gels made of hybrid organic/inorganic polymers, s ynthesized through the sol-gel method, composed of poly-(ethylene oxide) or poly-(propylene oxide) chains, and grafted on silica through urea bridges, have been studied by steady-state and time-resolved photoluminescence tech niques. These nanocomposite materials consist of two distinguished subphase s, an organic and an inorganic one. The volume fraction of the organic (pol yether) subphase is larger than that of the inorganic (silica) subphase, an d it increases with increasing polyether chain size. The condensation of th e silica subphase provides luminescent entities emitting light by electron- hole recombination on delocalized states associated with the active chemica l species of the urea bridges. Materials with smaller polyether chains are more luminescent than such with longer polyether chains. Divalent or trival ent cations introduced into these materials enhance the luminescence intens ity by solubilization close to the silica cluster surface and thus by decre asing surface defects and the ensuing quenching mechanism.