Excitonic effects in the photoluminescence (PL) of Si/SiO2 multiple quantum wells are investioated. The structures were fabricated by remote plasma-enhanced chemical-vapor deposition and subsequent rapid thermal annealing which leads to the formation of nanocrystalline Si well layers. In addition to distinct confinement features, the energy splitting between excitonic singlet and triplet states is derived as a function of the Si layer thickness. Anomalous temperature dependence and sublinear dependence of the PL intensity on optical excitation power are observed. These effects result from the interplay between the occupation of dark triplet states and thermal activation of: excitons into optically active singlet states. (c) 2006 American Vacuum Society.