2.5 eV Pulsed Cathodoluminesce band of silicon dioxide

Room-temperature (RT) Pulsed Cathodoluminescence (PCL) spectra of a set of pure synthetic (both crystalline and amorphous) silicon dioxide materials were studied. It is shown, that the PCL spectra of all samples (both amorphous and crystalline) possess a separate band at 495 nm (2.5 eV). This band is the most intensive one in PCL spectra of disordered materials. The RT PCL band at 495 nm (2.5 eV) of {\alpha}-quartz single crystal is polarized in XY crystalline plane (perpendicular to the $3^{rd}$ order symmetry axis). The structure of this band was detected. It consists of three peaks: at 480$\pm$2 nm (2.58$\pm$0.01 eV), 487$\pm$ nm (2.55$\pm$0.01 eV) and 493$\pm$2 nm (2.52$\pm$0.01 eV). Energy separation between peaks is equal in order of magnitude to energies of $Li_{x}O_{y}$ molecular vibrations and to the energy of optical phonon in {\alpha}-quartz. It is shown, that the emission band at 495 nm (2.5 eV) in RT PCL spectra of {\alpha}-quartz single crystal is related to the bulk emission centers, not to the surface-related ones. The annealing behaviors of the 495 nm (2.5 eV) bands in spectrum of amorphous and crystalline $SiO_{2}$ are close to each other. This fact may be the manifestation of identical origin of these bands. The following explanation of experimental data is proposed: the origin of 495 nm (2.5 eV) band in pure silicon dioxide is related to the recombination of non-bridging oxygen $NBO^{-}-Li^{+}$ centers.