Abstract
The sources of an absorption band at ∼5 eV observed in : and glasses have not been unambiguously identified. Results reported here are consistent with the source of two types of neutral oxygen vacancies. Samples of : and : were prepared by a chemical vapor deposition soot-remelting method. Optical-absorption and electron paramagnetic resonance spectra were measured. An absorption band centered at 5 eV in as-prepared : glasses is composed of two components. One has a peak at 5.06 eV and a FWHM (full width at half maximum) of 0.38 eV. Illumination with uv light bleached this band, and generated Ge E’ centers. A linear relation was found between the decrement in the intensity of the 5.06-eV component and the concentrations of uv-induced Ge E’ centers. This relation is a basis for attributing the defect responsible for this component to the precursors of uv-induced Ge E’ centers. We propose that the 5.06-eV band is due to neutral oxygen monovacancies (NOV’s) coordinated by two Ge ions. The oscillator strength of this band was evaluated to be approximately 0.4±0.1 assuming that the NOV’s are converted into Ge E’ centers by absorption of uv quanta. The activation energy for this conversion process was of the order of eV.
The second component of the absorption spectra has a peak at 5.16 eV and a FWHM of 0.48 eV. This band is not bleached but emits luminescence bands at 3.2 eV (intense) and 4.3 eV (weak) when irradiated with 5-eV light. Based on other research, we assign this band to ions coordinated by two oxygens and having two lone pair electrons (neutral oxygen divacancies). The concentrations of ions were much larger than those of the NOV’s and the ratio of the NOV’s to ions increases with increasing content. A similarity was found in the characteristics of these two types of oxygen-deficient defects to those in glasses.
- Received 28 May 1992
DOI:https://doi.org/10.1103/PhysRevB.46.11445
©1992 American Physical Society