Sn O 2 nanocrystals are grown in silica starting from a sol-gel method and using Er doping to passivate the cluster boundaries. As a result, emission at 3.8eV from the decay of SnO2 free excitons is observed in nanostructured SnO2:SiO2, besides the extrinsic 2eV luminescence of defects in SnO2 and ascribable to substoichiometric nanocluster boundaries. The analysis of the extrinsic emission competitive with the ultraviolet (UV) luminescence evidences the involvement of a phonon mode at 210cm−1 from a SnO-like phase. The feasibility of passivated wide-band-gap nanocrystals in silica gives interesting perspectives for UV-emitting optical devices.