The effects on the photoluminescence (PL) from Si nanocrystals embedded in a SiO2 matrix (Si-NCs/SiO2) by annealing in air have been examined, and the correlation between the PL properties and the pas sivation of luminescence-quenching defects at the Si nanocrystal/SiO2 interface has been studied. Si-NCs/SiO2 were fabricated by annealing amorphous silicon suboxide (a-SiOx) in a N-2 atmosphere at 1100 degrees C and the passivation of Si-NCs/SiO2 was performed by annealing Si-NCs/SiO2 in air at temperatures ranging from 400 to 800 degrees C for varied times. The heating of Si-NCs/SiO2 in air is very effective for passivating dangling bonds and an enhancement about 5 times in PL intensity was obtained. High-temperature passivation in air is accompanied by oxidation of Si nanocrystals. Additional N2-treatment of the passivated SiNCs/SiO2 at elevated temperatures depassivates Si-NCs/SiO2, generating new dangling bonds which can also be pas sivated in the subsequent repassivation process. The effect of pas sivation on the PL intensity is reversible, while high-temperature pas sivation results in an irreversible blue shift of PL spectra. PL decay time can be indicative of passivating or generating of dangling bonds. (C) 2014 Elsevier B.V. All rights reserved.