Radiation-induced coloring and paramagnetic centers in synthetic SiO2:Al glasses

Abstract

Optical absorption bands and paramagnetic centers induced with γ-rays or excimer laser lights were examined in high purity synthetic SiO2:Al glasses prepared by VAD method. Gamma-induced absorptions ranging 1.5–6.2 eV were deconvoluted into 5-Gaussian components peaking at 2.3, 3.2, 4.1, 4.9 and 5.8 eV. Two paramagnetic EPR centers associated with an Al ion were observed, Al-OHC and Al E' center and both centers are close to each other. These results indicate that a hole and an electron generated by irradiation are predominantly trapped at an oxygen bridging an Al and a Si and an Al coordinated with only three oxygens, respectively. A close correlation between 5-optical bands except the 5.8-eV band and Al-OHC/Al E′-center was obtained. It was assigned from a consideration of the nature of these Al-related centers that a band peaking at 2.3 eV are due to Al-OHC and Al E' centers give a band peaking at 4.1 eV. Oscillator strength was evaluated to be 0.06 for the 2.3 eV-band or 0.2 for the 4.1 eV-band. Although no coloring and paramagnetic centers were noted for XeCl laser light (304 nm), the results for ArF laser light (193 nm) were almost the same as the case of γ-irradiation. This difference suggests that a pair generation of Al-OHC and Al E'-center occurs via two photon process.