First principles calculations of electronic structure and optical properties for radiation-induced oxygen related defects in silica glass

Prolonged exposure of silica glass to radiation environments leads to the degradation of optical properties, significantly compromising the performance of optical systems. This study systematically investigates oxygen-related radiation-induced defects through first-principles calculations. Two primary defect types are characterized: non-bridging oxygen defects comprising a radical oxygen atom and a triple-coordinated silicon atom formed by Si-O bond rupture under irradiation, and oxygen vacancy defects featuring two adjacent triple-coordinated silicon atoms created through oxygen displacement by high-energy particles, which may subsequently transform into E' color centers. The electronic structure and optical properties of both the pristine 90-atom silica glass model and the defect models that may arise during irradiation have been systematically investigated. Calculations show an improved band gap value of 9.4 eV for pristine silica glass. Several new occupied and unoccupied defect states are found near the valence band maximum and in the band gap from the defect models. As the distance between the defect-related atoms increases, the valence band maximum moves away from the highest occupied state energy level, while the lowest unoccupied state shifts to lower energies, leading to a red-shift in the absorption spectrum. The calculated absorption peak positions are found to closely match the published experimental measurements.