Optical absorption band at 5.8 eV associated with the Eγ' centers in amorphous silicon dioxide: Optical absorption and EPR measurements

Line shape modifications induced by thermal treatment in the optical absorption and electron paramagnetic resonance (EPR) signals associated with the Eγ' center are experimentally investigated in various types of γ-irradiated amorphous silicon dioxide (a-SiO2). The g values of the EPR main resonance line of the Eγ' center show a shift correlated with the peak energy variation of the absorption band at about 5.8 eV associated with this defect. These spectroscopic changes are proposed to originate from structural modifications of the defect environment. The correlation is theoretically explained considering that the spin-orbit interaction couples the g-tensor's elements and the electronic energy level distribution of the defect. Our results suggest that the optical band at 5.8 eV is due to an intracenter electron promotion from the Si-O bonding states to the dangling bond of the O≡Si moiety