Strong and stable blue photoluminescence (PL), visible to the naked eye under 0.4 μW of 300 nm and 2.7 μW of 370 nm excitation, has been observed for samples of Si clusters embedded in SiO2 matrices, prepared by rf co-sputtering followed by N2 annealing at 800 °C. Si K-edge extended x-ray absorption fine structure (EXAFS) and near-edge x-ray absorption fine structure (NEXAFS) strongly suggest the existence of Si nanoclusters with crystalline cores in the efficient emitting material. The PL excitation dependence is explained by an increase in the conduction band density of states deep in the band, and the formation of a band tail.

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