Silicon dioxide thin film luminescence in comparison with bulk silica

The luminescence of the self-trapped exciton (STE) in SiO₂ films was measured at low temperatures on the background of defect luminescence under cathodoexcitation and compared with bulk silica luminescence. The defect luminescence is mainly caused by non-bridging oxygen centers (a red luminescence band at 1.8 eV) and twofold coordinated silicon centers (blue and ultraviolet luminescence with 2.7 and 4.4 eV bands, respectively). The STE luminescence with a band at 2.3 eV is uniformly distributed within SiO₂ film volume. Contrary to defect luminescence, whose intensity increases with irradiation time, the STE luminescence decreases almost to zero in a few seconds of irradiation time. The defect luminescence increase is attributed to transformation of precursors whereas STE luminescence is produced in the continuous network. The decrease of STE luminescence is attributed to radiation damage in the continuous network.