Showing papers by "E. J. Friebele published in 1983"

Fundamental defect centers in glass: Electron spin resonance and optical absorption studies of irradiated phosphorus‐doped silica glass and optical fibers

Abstract: Defect centers induced by ionizing radiation (50–100‐keV x rays, 60Co γ rays) in high purity P‐doped silica glass have been observed and elucidated by ESR spectroscopy. Four generic species are well characterized on the basis of the observed 31P hyperfine splittings and g values as defects analogous to PO2−3 (phosphoryl), PO4−4 (phosphoranyl), PO2−2 (phosphinyl), and PO2−4 radicals. The latter species, also termed the phosphorus‐oxygen‐hole center (POHC), is shown to occur in two variants comprising holes trapped on one or two nonbridging oxygens. Radiation‐induced Si E′ centers with and without P next‐nearest‐neighbors were also identified, and a singlet resonance S due to E′ type defects such as (OSi2)Si⋅ and/or (O2Si)Si⋅ was observed to grow in with annealing above ∼800 K, regardless of whether or not the sample was irradiated. The structures, formation mechanisms, and precursors of these defects have been determined or inferred for all centers. Radiation‐induced optical absorption spectra over the ran...

ESR studies of damage processes in X‐irradiated high purity a‐SiO2:OH and characterization of the formyl radical defect

Abstract: A range of high purity type III synthetic silicas (Suprasil 1, Spectrosil, Dynasil 1000) has been subjected to 100 keV X irradiation at 77 K and the induced ESR spectra have been recorded at 100 K before and after successive pulse anneals to higher temperatures. Absolute spin concentrations are determined as functions of radiation dose, anneal temperature and time, prior irradiation history, and sample supplier. Defects monitored comprise E′ centers, oxygen‐associated hole centers (OHCs), atomic hydrogen, and a previously unidentified defect in a‐SiO2 characterized by a 13.3 mT doublet centered on g=2.0. The 13.3. mT doublet is ascribed here to formyl radicals HCO produced by the reaction of radiolytic hydrogen atoms with minute amounts (≲0.1 ppm) of dissolved carbon monoxide present in Suprasil 1 and Dynasil 1000 but not Spectrosil. This identification is based on production kinetics and the similarity of the spin Hamiltonian parameters measured at 30 K to those previously reported for the formyl radical...

Observation of the methyl radical CH3. in irradiated, high-purity synthetic fused silica

Abstract: Stable methyl radicals CH3. have been observed in irradiated high-purity synthetic silicas by electron spin resonance techniques. Analysis of the dependence of the linewidth on the nuclear spin quantum number of the ESR spectrum demonstrates that the radicals tumble at a frequency of ∼ 11 MHz. We suggest that this small tumbling rate as compared with the “free” rotation rate of 10 GHz is due to interaction of the radical with the glass network. Radicals were observed in concentrations of ∼ 3 × 1013/g SiO2 in samples fused in a hydrocarbon-oxygen flame, but no radical concentration could be measured in samples fused in either an electric arc or hydrogen-oxygen flame. The methyl radical is presumed to form by radiodissociation of either CH4 or CO dissolved in the silica during the fusion process and subsequent reaction of C with radiolytic H.

Radiation-induced defects in glasses with high water content

Abstract: Na 2 O3SiO 2 glasses containing up to 17 wt. % H 2 O have been x-irradiated at 77K and studied by ESR and optical techniques as a function of anneal temperature. It is shown that the radiation-protected characteristic of hydrosilicate glasses containing > 2 wt. % water is related to the postirradiation reaction of H 2 O molecules with HC 1 and HC 2 hole centers to form free OH° radicals, observed for the first time in glasses.