Probing densified silica glass structure by molecular oxygen and E' center formation under electron irradiation.

This study aims to learn more about the structure of densified silica with focus on the metamict-like silica phase (density = 2.26 g/cm3) by examining the formation of E' point defects and interstitial molecular oxygen O2 by 2.5 MeV electron irradiation. High-dose (11 GGy) irradiation creates a metamict-like phase and a large amount of interstitial O2, which is destroyed upon subsequent additional lower-dose electron irradiation. The O2 cathodoluminescence (CL) data indicate that the formation of O2 from peroxy linkages Si-O-O-Si in silica network is strongly dependent on the intertetrahedral void sizes. The position and shape of the O2 emission line support the idea that the configuration of these voids in metamict phase is close to that of non-densified silica. Moreover, data support the strong correlation between the formation of 3-membered rings of Si-O bonds and E'-centers when silica density increases from 2.20 to 2.26 g/cm3.

Oxygen-related intrinsic defects in glassy SiO2: interstitial ozone molecules

Interstitial O3 molecules in 7.9 eV photon-irradiated silica are identified. Their optical absorption band at 4.8 eV nearly coincides with the 4.8 eV band of nonbridging oxygen hole centers. The O3-related band is distinguished by a smaller halfwidth (0.84 vs 1. 05 eV), by susceptibility to ultraviolet bleaching, by lack of correlation to the 1.9 eV luminescence band, and by rise of a singlet O2 luminescence band at 0.974 eV during photobleaching. This identification solves a long controversy on the nature of optical bands in silica and gives a tool for studying the mobility of atomic oxygen in SiO2.

Photochemical processes induced by 157-nm light in H(2)-impregnated glassy SiO(2):OH.

F(2) excimer-laser irradiation induces two major changes in SiO(2): OH glass impregnated with H(2) molecules. First, the vacuum-UV optical absorption edge is bleached, and the absorption at 157 nm decreases from 0.95 to 0.68 cm(-1) . Second, preexisting free SiOH groups and interstitial H(2) are photochemically converted to hydrogen-bonded hydroxyl groups. It is suggested that the bleaching of the UV-absorption edge is caused by a change of OH groups from a free to a hydrogen-bonded state and by photolysis of distorted Si-O bonds that are absorbing in the edge region.

Fluorine-doped SiO2 glasses for F2 excimer laser optics: fluorine content and color-center formation.

Color-center formation in F-doped, OH-free synthetic SiO(2) glasses by irradiation with F(2) excimer lasers (157 nm) was examined as a function of the F content. The concentration of photoinduced E(') centers was reduced to approximately 1/20 by 1 mol.% F(2) doping and remained almost constant on further doping to 7.3 mol. %. The absorption edge was considerably shifted to a lower wavelength (157.4 nm -->153 nm for a 5-mm-thick sample) by 1-mol. % doping and decreased only slightly on further doping. The intensities of the Raman bands that are due to three- and four-membered ring structures were significantly reduced by 1-mol. % F doping. These results strongly suggest that elimination of strained Si-O-Si bonds by F doping plays a central role in the improvement of radiation resistance of SiO(2) glasses to F(2) laser light.