Photoluminescence (PL) of Si nanocrystals with annealing in CO2 was studied using the continuous and time-resolved PL measurements. The PL intensity enhances as annealing temperature increases, which is attributed to passivation of the nonradiative recombination centers. As the annealing temperature is 950 degrees C the PL intensity has a maximum value, which increases about a factor of 3 than that of the untreated sample. Based on the emission energy dependence of the PL decay time, the depth of carrier localization is found to increase after the annealing in CO2. We suggest that the oxygen atoms desorbed from CO2 diffuse to react with Si nanocrystals and introduce localized states at the Si/SiO2 interface. (C) 2007 Elsevier B.V. All rights reserved.