Photoluminescence and optical absorption in neutron-irradiated crystalline quartz

Optical absorption measurements in the 3.5-6.5 eV spectral range and photoluminescence spectra, excited in the 4-8 eV range have been performed on neutron irradiated synthetic crystalline quartz as a function of temperature and of neutron fluence. The Gaussian deconvolution of the radiation-induced absorption spectrum in the 4.5-6 eV region reveals a complex structure: five distinct components, peaking at 4.85, 5.06, 5.35, 5.62, and 5.96 eV are detected. The complexity of the absorption pattern finds a correspondence in photoluminescence spectra excited in the 5 eV region: a detailed analysis of the emission spectra as a function of excitation energy indicates the presence of three emission bands centered at 3.91, 4.23, and 4.46 eV, excited at 5.25, 4.83, and 5.03 eV respectively. Excitation in the 5.62 and 5.96 eV absorption peaks does not produce emission. The features of the 4.23 eV and of the 4.46 eV bands are very similar to those of the alpha(intrinsic) emission, already well studied in amorphous SiO2: this suggests a possible correlation between these bands and the alpha(intrinsic) center. The 3.91 eV band does not find a correspondence in amorphous SiO2, and so the responsible defect appears specifically related to the crystalline structure. The emission spectra excited in the E absorption band (approximate to 7.6 eV) present a weak band centered at 4.83 eV: its dependence on neutron irradiation dose suggests the attribution to an intrinsic center different from those responsible for the emission in the 3.8 - 4.5 eV region.