SPECTRAL AND KINETIC-PROPERTIES OF THE 4.4-EV PHOTOLUMINESCENCE BAND IN ALPHA-SIO2 - EFFECTS OF GAMMA-IRRADIATION

Spectral and decay properties of the photoluminescence (PL) emission i n the range 3.5-5.0 eV are investigated in various types of silica (a- SiO2), as grown and after gamma irradiation. We report experimental re sults on the ultraviolet (5.0 eV) absorption, on the emission and exci tation spectra of the stationary FL, excited by ultraviolet (5.0 eV) a nd vacuum ultraviolet (6.0-8.5 eV) light, on the decay times of the tr ansient PL emission, at room temperature, and at 10 K. Our results sho w that gamma irradiation causes the appearance of a PL band, centered at 4.37 eV, which can be excited at 5.0 eV and at 6.8 eV. This band, w hich is induced in all the investigated samples, brings a close simila rity to the PL band alpha(1) that is peculiar of unirradiated oxygen-d eficient natural silica. However, small but appreciable differences be tween the two bands can be inferred from our experimental data. The re sults are consistent with an energy level scheme with two singlet-sing let transitions. We tentatively ascribe the small differences between the two PL bands to different dynamic environments surrounding the int rinsic and the gamma-induced centers.