EXPERIMENTAL-EVIDENCE OF THE COMPOSITE NATURE OF THE 3.1-EV LUMINESCENCE IN NATURAL SILICA

The 3.1 eV photoluminescence of silica has been investigated on severa l samples of commercial origin, by measuring both time-resolved and st ationary spectra. This structure, known as the beta band, displayed th e well known peculiarities: 3.1 eV energy position, 0.4 eV full width at half maximum, excitation peak at 5.1 eV and 100 mu s decay time. Ho wever, an accurate analysis of the experimental data has shown the dou ble nature of the beta band in all natural silica samples here studied . The characteristic values of the two components beta(1) and beta(2) are: peak energy 3.04 and 3.20 eV, full width at half maximum of 0.44 and 0.35 eV and decay time of 115 and 97 mu s respectively. In additio n the intensity ratio between the luminescent emissions at 3.1 and 4.2 eV was found to be constant in the whole set of samples. The occurren ce of two beta components with so close spectral and time peculiaritie s might be ascribed to fluorescence processes involving the same oxyge n deficient centers surrounded by two slightly different environments.