Infrared characterization of aluminum and hydrogen defect centers in irradiated quartz

Abstract

As-received and 60Co-irradiated cultured quartz is characterized using low-temperature near-infrared Fourier spectroscopy, and peaks associated with as-grown hydroxide (OH) and aluminum hydroxide (Al-OH) point-defect centers are measured. Defect-center distributions are determined from scanning small crystal regions parallel or normal to the crystal-growth axis. Large variations in point defects are observed arising from variations in substitutional and interstitial impurity concentrations along the crystal-growth axis. For the initial radiation doses as-grown OH decreases uniformly across the crystal and forms Al-OH, but Al-OH peak strength varies considerably in different crystal sections. This indicates the possibility of radiation-induced hydrogen diffusion over large distances to compensate nonuniformities in aluminum-ion distribution. With increasing dose as-grown OH may stabilize to a constant level in some crystal regions but deplete in other sections. For some crystals, Al-OH continues to form even after all as-grown OH is depleted, indicating an additional internal hydrogen-ion source. Sweeping (electrodiffusing) an irradiated sample in an air atmosphere restores as-grown OH, retains the radiation-induced Al-OH, and in samples with high as-grown OH concentrations creates a series of small bands in the frequency range of 3450 to 3625 cm−1.