The absorption and emission spectra of silicon nanocrystals up to $1\mathrm{nm}$ diameter have been calculated within a first-principles framework. Our calculations include geometry optimization and the many-body effects induced by the creation of an electron-hole pair. Starting from hydrogenated silicon clusters of different sizes, different $\mathrm{Si}∕\mathrm{O}$ bondings at the cluster surface have been considered. We found that the presence of a $\mathrm{Si}\mathrm{O}\mathrm{Si}$ bridge bond causes significant excitonic luminescence features in the visible range that are in fair agreement with experiment.

• Received 4 October 2006

DOI:https://doi.org/10.1103/PhysRevB.75.033303