In this paper, we have studied the evolution of the photoluminescence (PL) emission from US quantum dots embedded in silica glass with time. An increase of PL emission with time was observed due the passivation of non-radiative recombination centres. Annealing of the samples in different environments (oxygen, hydrogen, and air) seems to reduce the PL emission, due to the activation of non-radiative defect states. (c) 2005 Elsevier B.V. All rights reserved.