Photoluminescence from Sol−Gel Organic/Inorganic Hybrid Gels Obtained through Carboxylic Acid Solvolysis

Hybrid organic/inorganic sol−gel materials have been synthesized by carboxylic acid solvolysis of (aminopropyl)triethoxysilane or ureasil precursors. The hybrid nature of these gels is expanded with the introduction of silica esters. A main feature of the ensuing materials is the formation of hybrid organic/inorganic nanoclusters, which are founded on silica backbone but they are facilitated and assisted also by forces arising from hydrophilic/hydrophobic balance and hydrogen-bonding interactions. The silicious domains of these clusters with attached functional groups, for example, amino groups, are luminescence centers. Some precursor compounds bearing amino groups without silicious groups but with a tendency to form clusters in solution also emit luminescence. Luminescence is the result of electron−hole recombination on delocalized states so that emission wavelength depends on excitation wavelength. Luminescence can thus be emitted in almost the entire visible spectrum and it can be tuned by choosing excitation wavelength. Amino-group-containing gels give the highest photoluminescence yield. It is, generally, expected that the presence of chemical groups with electron-donating capacity within the light-generating nanoclusters will be a favorable factor for making an efficient photoluminescent gel.