EXAFS, SAXS and Eu3+ Luminescence Spectroscopy of Sol-Gel Derived Siloxane-Polyethyleneoxide Hybrids

Hybrid Eu³⁺-doped silica-poliethyleneoxide (PEO) nanocomposites with covalent bonds between the inorganic (siloxane) and organic (PEO) phases have been obtained by sol-gel process. These materials are transparent, flexible and present high Eu³⁺ luminescence output. Their luminescence properties, local environment around europium ions and structure have been investigated as a function of europium content. EXAFS measurements indicate that the increase in Eu-doping induces a decrease in Eu³⁺ coordination number. An increase in symmetry degree around the metal ion is also observed for increasing Eu³⁺ concentration, while non radiative decay paths from the ⁵D₀ excited state become more important. SAXS results suggest the preferential interaction of europium ions with ether-type oxygens of the polymer chains. However, the existence of interactions between the cations and the carbonyl groups from urea bridges located at the siloxane-PEO interface can not be excluded.