The origin of photoluminescence lines in irradiated amorphous SiO2

Irradiation of amorphous SiO₂ produces defects with a characteristic photoluminescence line at 1.9 eV (∼ 630 nm) that is universally attributed to a nonbridging oxygen atom. We present results of first-principles calculations that describe a complete cycle of electronic transitions (absorption + luminescence) and show that two different defects are equally likely to be responsible: nonbridging oxygen atoms and hydroxyl (OH) groups weakly bonded to fourfold coordinated network Si atoms.