Changes in optical absorptions in natural quartz irradiated by γ-rays and its isochronal annealing

The clear natural Brazilian quartz used in this experiment had a weak optical absorption at the A1-band (1.85-2.0 eV) before γ-ray irradiation. By irradiating the sample, a strong A2-band absorption (2.65-2.75 eV) was produced, while the A1-band absorption increased only very slightly, although both the A1- and A2-bands are related to an aluminum impurity. The thermal activation process of the A2-band absorption was investigated by isochronal annealing to evaluate the activation energy. When possible losses were taken into consideration, an activation energy E=0.32 eV was obtained, where the losses are light transmission losses originating from multiple scattering, absorption by surface damage, and scattering in random directions by the surface roughness of a specularly polished quartz plate. When an ideal state was assumed, in which the transmission losses did not exist, an activation energy E=0.28 eV was obtained. From these results, the activation energy for this color center is evaluated to be 0.3±0.2 eV. (author)