Effect of treatment at high temperature (HT) (up to 1200 degrees C) under high hydrostatic pressure (HP) (up to 1.5 GPa) on the photoluminescence (PL) of silicon dioxide films was investigated. The authors found that the PL intensity of the oxide films grown in pure oxygen can be significantly enhanced by the HT-HP treatment. Four PL peaks, at wavelengths of about 570, 620, 720, and 950 nm, were found. The 570 and 950 nm peaks are attributed to the defect centers and amorphous Si, respectively. The luminescence at 620 and 720 nm is' attributed to the quantum confinement effect involving the silicon nanocrystallites embedded in the oxide film. The PL intensities are strongly governed by the preparation conditions of the as-grown oxide layer as well as by the annealing conditions. Raman study indicates that both amorphous and crystalline Si phases coexist in the HT-HP processed samples. The formation of Si nanocrystallites is attributed to the phase separation effect involving Si suboxide. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3025838]