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Abstract: We report the evolution of photoluminescence (PL) of Si nanocrystals (nc-Si) embedded in a matrix of SiO2 during Ar+ ion bombardment. The integrated intensity of nc-Si PL falls down drastically before the Ar+ ion fluence of 1015 ionscm−2, and then decreases slowly with the increasing ion fluence. At the meantime, the PL peak position blueshifts steadily before the fluence of 1015 ionscm−2, and then changes in an oscillatory manner. Also it is found that the nc-Si PL of the Ar+-irradiated sample can be partly recovered after annealing at 800°C in nitrogen, but can be almost totally recovered after annealing in oxygen. The results confirm that the ion irradiation-induced defects are made up of oxygen vacancies, which absorb light strongly. The oscillatory peak shift of nc-Si can be related to a size-distance distribution of nc-Si in SiO2. [Copyright &y& Elsevier]