Journal of Physics - Condensed Matter vol:17 issue:38 pages:L393-L398
Point defects in fumed similar to 7 nm sized silica nanoparticles have been studied by means of K- and Q-band electron spin resonance following photodissociation of H from passivated defects. Generally, the spectra are dominated by the presence of intrinsic oxygen-associated hole centres (OHCs), probably of two types, one of which could be identified as the peroxy radical (O-3&3bond; Si-O-O center dot). Determination of the upper limit of the density of all defects observed suggests that, in conflict with previous inference, OHCs cannot account for the observed optical band gap narrowing. Probably that effect is related instead to nm size induced structural alterations in the SiO2 network.