Studies on Hybrid Organic/Inorganic Nanocomposite Gels Using Photoluminescence Techniques

Summary.:  Transparent nanocomposite gels made of hybrid organic/inorganic polymers, synthesized 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 techniques. These nanocomposite materials consist of two distinguished subphases, an organic and an inorganic one. The volume fraction of the organic (polyether) subphase is larger than that of the inorganic (silica) subphase, and it increases with increasing polyether chain size. The condensation of the silica subphase provides luminescent entities emitting light by electron-hole recombination on delocalized states associated with the active chemical species of the urea bridges. Materials with smaller polyether chains are more luminescent than such with longer polyether chains. Divalent or trivalent cations introduced into these materials enhance the luminescence intensity by solubilization close to the silica cluster surface and thus by decreasing surface defects and the ensuing quenching mechanism.