Experimental evidence of the composite nature of the 3.1 eV luminescence in natural silica

Abstract The 3.1 eV photoluminescence of silica has been investigated on several samples of commercial origin, by measuring both time-resolved and stationary spectra. This structure, known as the β band, displayed the well known peculiarities: 3.1 eV energy position, 0.4 eV full width at half maximum, excitation peak at 5.1 eV and 100 μs decay time. However, an accurate analysis of the experimental data has shown the double nature of the β band in all natural silica samples here studied. The characteristic values of the two components β1 and β2 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 μs respectively. In addition 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 occurrence of two β components with so close spectral and time peculiarities might be ascribed to fluorescence processes involving the same oxygen deficient centers surrounded by two slightly different environments.