Visible photoluminescence (PL) bands around 2 eV were studied in 60Co γ-irradiated (dose<1 MGy) oxygen-deficient-type amorphous SiO2 (a-SiO2) excited by 2–4 eV photons. In addition to the well-known 1.9 eV PL band due to nonbridging oxygen hole centers, another PL band was observed at 2.2 eV when excited by 3.8 eV photons. The intensity of the 2.2 eV band increases with decreasing oxygen partial pressure during the sample preparation. Electron-spin-resonance measurements show that the intensity of the 2.2 eV band is correlated with the concentration of the Eδ′ center, a paramagnetic state of a cluster of silicons. After much higher γ irradiation with a dose up to 10 MGy, a new PL band was induced at 1.75 eV under excitation by 2.5 eV photons, as well as the 1.9 and 2.2 eV PL bands. By comparing its spectral shape and excitation energy with known PL band in Si-implanted a-SiO2, it is suggested that the 1.75 eV band is associated with Si nanocrystals formed from Si clusters in a-SiO2 by the high-dose γ irradiation.
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Photoluminescence (PL) study was performed on B or P ion-implanted thermal SiO2 films. Two PL bands at 4.3 and 2.6 eV were observed. For the 4.3 eV bands, two PL excitation (PLE) bands were observed at 5.0 and 7.4 eV. Based on the close similarities of the PL and PLE bands to those observed in oxygen-deficient-type bulk silica, the 4.3 and 2.6 eV PL bands are ascribed to the oxygen-deficient-type defects induced by ion implantation. While the 4.3 eV PL band in the bulk SiO2 decays exponentially, the decay of the corresponding PL band in the implanted thermal SiO2 films follows a power low or stretched exponential, suggesting the distribution of PL lifetimes. This suggests that the oxygen-deficient-type defects induced by the ion implantation in thermal SiO2 films are perturbed by the structural distribution of the surrounding Si-O-Si network, including the concentration of PL quenching centers.
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