Effects of intrinsic defects on the electronic and optical properties of amorphous silica: First principle study

摘要

The electronic and optical properties of glass are rather sensitive to the variation of its atomic structure. The effect of intrinsic defects in amorphous structures of silica (a-SiO₂) has shown to create electron trap level in the electronic band gap. The atomic structure of the amorphous material has been constructed from Rietveld Refinement. The study was carried out using plane-wave pseudo potential via density functional theory (DFT). Electron trap energy level formed within the 5.80 eV band gap of oxygen-excess defect a-SiO₂ is due to relatively high- density of unpaired electrons of -O in the O 2p orbital. The electron trap level of the defect-state was found to be lower as the number of excess oxygen atoms increased. An experimental study on the photoluminescence (PL) of an undoped-SiO₂ glass produced a number of radiative emissions across a broad bandwidth when excited from 325-nm, 200-mW laser. It would not be possible for an electron to be excited to the conduction band of rather large 5.85-eV band gap when excited with a 325- nm-wavelength (3.81 eV) laser. Thus, these excited electrons are believed to have trapped at metastable levels within the bandgap and released radiative photon energy when transiting down to ground state. One particular emission spectrum, which is at 388-nm-wavelength resulted from radiative 3.20-eV photon energy emitted from the electron trap level of 3-excess oxygen defective states in the structure.