Si nanoclusters were formed by Si-28 ion implantation into SiO2 matrix and subsequently annealed at 1050 degrees C for 2 h under N-2 ambient. The photoluminescence (PL) characteristics depend on the Si-28 fluence. The PL signals seen at around 775 mn and 825 nm are assigned to light emitting centers connected to formation of Si clusters, for 5 x 10(16) cm(-2) and 1 x 10(17) cm(-2) Si-28 fluences, respectively. Defect-related light emission observed at around 625 nm emerges only in the case of high implantation fluence. These sample sets were post implanted with Si-28 ions at fluences between 1 x 10(12) and 1 x 10(14) cm(-2) to monitor the variations in PL emission as a function of post implantation fluence. The PL emission decreases and exhibits a blue-shift with increasing post implantation fluence and quenches totally when the fluence exceeds a certain value, while the peak seen at 625 nm which is related to matrix defects is enhanced after the post implantation. Upon thermal annealing, the PL peaks measured at 775 nm and 825 nm recovered and reached the intensity of the peak before the post implantation. The variations in the PL peak with the implantation fluence and annealing conditions are ascribed to the different structure of Si nanoinclusions in the SiO2 matrix. (c) 2006 Elsevier B.V. All rights reserved.