White-Light Emission of Amine-Functionalized Organic/Inorganic Hybrids:  Emitting Centers and Recombination Mechanisms

This work discusses the recombination mechanisms and the chemical nature of the emitting centers subjacent to the white-light emission of sol−gel derived amine-functionalized hybrids lacking metal activator ions, such as those based on 3-aminopropyl)triethoxysilane (APTES), 3-glycidyloxypropyltrimethoxysilane (GPTES), and on urea and urethane precursors. The white-light photoluminescence (PL) results from a convolution of the emission originated in the NH (NH2) groups of the urea or urethane bridges (APTES- and GPTES-based hybrids) with electron−hole recombinations occurring in the siloxane nanoclusters. These two components reveal a radiative recombination mechanism typical of donor−acceptor pairs, mediated by some localized centers. Photoinduced proton-transfer between defects such as NH3 + and NH- (GPTES- and APTES-based hybrids) or NH2 + and N- (di-ureasils and di-urethanesils) is proposed as the mechanism responsible for the NH-related component. Electron paramagnetic resonance data suggest that the specific PL mechanism subjacent to the component associated with the siliceous nanodomains involves oxygen-related defects.