A well defined type of oxygen deficiency has been induced in the silica network by introducing Si - Si groups through a molecular doping based on the sol-gel synthesis. In this material, we have investigated the visible and UV photoluminescence (PL), up to 7 eV, arising from localized states excited in the energy range 3-12 eV by synchrotron radiation. The PL excitation spectrum is dominated by one main sub-band-gap excitation band, peaked at 7.1 with a full width of half-maximum of 0.8 eV. No PL arises exciting at 5 eV, specifically no PL band at 4.4 and 2.7 eV are observed, ruling out the formation of twofold coordinated -Si-sites. These data confirm all previous theoretical and experimental assignments of transitions at about 7-8 eV to localized excitations of neutral-oxygen-vacancy (NOV) sites. Exciting in the vacuum-UV (VUV) above 7 eV, the investigated material does not show the typical 4.4 and 2.7 eV PL observed in fused silica. The peculiar NOV configuration appears to inhibit the photoconversion process responsible in fused silica for the VUV excitation of the twofold coordinated silicon emission. The main emission is peaked at about 3.7 eV, with a PL lifetime of about 1 mu s. A minor component with a much slower lifetime (800 mu s) has been detected at 2.9 eV, with a further minor excitation channel at about 6 eV. All emissions excited at 7.1 eV show an intensity decrease with the temperature, but a negligible thermal change of the lifetime. The results give an indication of the possible energy level structure of NOV and evidence an efficient nonradiative decay mechanism of the excited state, caused by a strong electron-phonon interaction during the VUV excitation of the defect. The analysis of the data suggests a large Si-Si bond relaxation of about 0.1 nm, giving definite experimental confirmation of previous theoretical calculations.
Paleari, A., Chiodini, N., DI MARTINO, D., Meinardi, F. (2005). Radiative decay of vacuum-ultraviolet excitation of silica synthesized by molecular precursors of Si-Si sites: An indicator of intracenter relaxation of neutral oxygen vacancies. PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS, 71(7) [10.1103/PhysRevB.71.075101].
Radiative decay of vacuum-ultraviolet excitation of silica synthesized by molecular precursors of Si-Si sites: An indicator of intracenter relaxation of neutral oxygen vacancies
PALEARI, ALBERTO MARIA FELICE;CHIODINI, NORBERTO;DI MARTINO, DANIELA;MEINARDI, FRANCESCO
2005
Abstract
A well defined type of oxygen deficiency has been induced in the silica network by introducing Si - Si groups through a molecular doping based on the sol-gel synthesis. In this material, we have investigated the visible and UV photoluminescence (PL), up to 7 eV, arising from localized states excited in the energy range 3-12 eV by synchrotron radiation. The PL excitation spectrum is dominated by one main sub-band-gap excitation band, peaked at 7.1 with a full width of half-maximum of 0.8 eV. No PL arises exciting at 5 eV, specifically no PL band at 4.4 and 2.7 eV are observed, ruling out the formation of twofold coordinated -Si-sites. These data confirm all previous theoretical and experimental assignments of transitions at about 7-8 eV to localized excitations of neutral-oxygen-vacancy (NOV) sites. Exciting in the vacuum-UV (VUV) above 7 eV, the investigated material does not show the typical 4.4 and 2.7 eV PL observed in fused silica. The peculiar NOV configuration appears to inhibit the photoconversion process responsible in fused silica for the VUV excitation of the twofold coordinated silicon emission. The main emission is peaked at about 3.7 eV, with a PL lifetime of about 1 mu s. A minor component with a much slower lifetime (800 mu s) has been detected at 2.9 eV, with a further minor excitation channel at about 6 eV. All emissions excited at 7.1 eV show an intensity decrease with the temperature, but a negligible thermal change of the lifetime. The results give an indication of the possible energy level structure of NOV and evidence an efficient nonradiative decay mechanism of the excited state, caused by a strong electron-phonon interaction during the VUV excitation of the defect. The analysis of the data suggests a large Si-Si bond relaxation of about 0.1 nm, giving definite experimental confirmation of previous theoretical calculations.
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