Photoluminescent silicon nanocrystals synthesized by reactive laser ablation

We report the synthesis of Si nanocrystals embedded in a SiO2 matrix using reactive laser ablation in oxygen atmosphere followed by annealing. We observe a strong photoluminescence signal, which is related to the oxygen background pressure used for synthesis. The average nanoparticle size, obtained independently by fitting photoluminescence spectra and from x-ray diffraction patterns, decreases from 16 to 2 nm with increasing oxygen pressure from 0.01 to 1.1 mTorr. The maximum photoluminescence intensity is observed at 0.8 mTorr, which corresponds to a crystal size of 2.2 +/- 0.4 nm. We find that the concentration of nonoxidized Si, which is controlled by the oxygen pressure, determines the final nanocrystal size.