PHOTOLUMINESCENCE BAND AT 4.4 EV IN OXYGEN-DEFICIENT SILICA - TEMPERATURE EFFECTS

We report experimental results on the spectral properties and time beh aviour of the 4.4 eV photoluminescence (PL) band in oxygen-deficient s ilica(a-SiO2). Our measurements, performed both at T = 300 K and T = 1 0 K, show that at room temperature the PL features are independent of the particular excitation energy (5.0 eV, 6.8 eV and 7.6 eV) whereas a t low temperature, upon excitation at 7.6 eV, the decay of the PL emis sion is faster than for lower excitation energies. This shortening of the PL lifetime is consistent with previously reported data, which wer e explained by hypothesizing an interconversion mechanism between two structural configurations of the same oxygen defect. Nevertheless, our results do not support the proposed mechanism and we tentatively sugg est a different interpretation of the experimental data.