A fiber preform with P-doped silica core is studied by luminescence methods. P-doped silica was synthesized via the SPCVD method on a substrate tube made of pure silica glass F300. Two luminescence bands were detected under excitation of the F2 excimer laser (157nm). One band is in UV range at 4.6eV (265 nm) with two time constants ~30ns and 5μs and the other at 3.1eV (400 nm) with time constant ~5.5ms. Fast decay of the blue band with time constant ~20ns was also observed. The main excitation band of the UV luminescence is at 7.1eV (~170 nm) and that for blue band is at 6.3eV (~195 nm). These bands belong to two different luminescence centers, however, both are associated with the presence of phosphorus. The UV band is similar to the one observed in many different oxide materials containing phosphorus and is ascribed to PO43- complex ion. The blue band is ascribed to a twofold coordinated phosphorus. Both the blue and the UV luminescences participate in the recombination process due to electron trapping. These luminescences appear due to thermal stimulation upon recombination of liberated self-trapped holes. Other than the detected phosphorus-related oxygen-hole-centers, there is no other recombination luminescence.

Luminescence of phosphorus doped crystalline alpha-quartz and phosphosilicate glass with content 3P(2)O(5) center dot 7SiO(2) was studied. Water and OH groups are found by IR spectra in these materials. The spectrum of luminescence contains many bands in the range 1.5-5.5 eV. The luminescence bands in UV range at 4.5-5 eV are similar in those materials. Decay duration in exponential approximation manifests a time constant about 37 ns. Also a component in mu s range was detected. PL band of its component is shifted to low energy with respect to that of similar to 37 ns component. This shift is about 0.6 eV. It is explained as singlet-triplet splitting of excited state. Below 14K increase of luminescence kinetics duration in Its range was observed and it was ascribed to zero magnetic field splitting of triplet excited state of the center.Yellow-red luminescence was induced by irradiation in phosphorus doped crystalline alpha-quartz, phosphosilicate glasses. The yellow luminescence contains two bands at 600 and 740 nm. Their decay is similar under 193 nm laser and may be fitted with the first order fractal kinetics or stretched exponent. Thermally stimulated luminescence contains only band at 600 nm. The 248 nm laser excites luminescence at 740 nm according to intra center process with decay time constant about 4 ms at 9 K.Both type of luminescence UV and yellow were ascribed to different defects containing phosphorus.P-doped alpha-quartz sample heated at 550 degrees C become opalescent. IR spectra related to water and OH groups are changed. Photoluminescence intensity of all three bands, UV (250 nm), yellow (600 nm) and red (740 nm) strongly diminished and disappeared after heating to 660 degrees C. Radiation induced red luminescence of non-bridging oxygen luminescence center (NBO) appeared in crystal after heat treatment. We had observed a crystalline version of this center (Skuja et al., Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms. 2012; 286: pp. 159-168). Effect of heat treatment explained as sedimentation of phosphorus in some state. Keeping of treated sample at 450-500 degrees C leads to partial revival of ability to create yellow luminescence center under irradiation. (C) 2015 Elsevier B.V. All rights reserved.

Luminescence of phosphate glasses such as CaO center dot P2O5 and SrO center dot P2O5 is compared with that of phosphorus doped crystalline -quartz and phosphosilicate glass with content 3P(2)O(5)center dot 7SiO(2). Water & OH groups are found by IR spectra in these materials. The spectrum of luminescence contains many bands in the range 1.5 -5.5 eV. The luminescence bands in UV range at 4.5-5 eV are similar in those materials. Decay duration in exponential approximation manifests a time constant about 37 ns. Also a component in mu s range was detected. PL band of mu s component is shifted to low energy with respect to that of similar to 37 ns component. This shift is about 0.6 eV. It is explained as singlet-triplet splitting of excited state. Below 14 K increase of luminescence kinetics duration in mu s range was observed and it was ascribed to zero magnetic field splitting of triplet excited state of the center. Yellow-red luminescence was induced by irradiation in phosphorus doped crystalline alpha-quartz,phosphosilicate glasses. The yellowl uminescence contains two bands at 600 and 740 nm. Their decay is similar under 193 nm laser and may be fitted with the first order fractal kinetics or stretched exponent. Thermally stimulated luminescence contains only band at 600 nm. The 248 nm laser excites luminescence at 740 nm according to intra center process with decay time constant about 4 ms at 9 K. Both type of luminescence UV and yellow were ascribed to different defects containing phosphorus. P-doped alpha-quartz sample heated to 550 co become opalescent. Ir spectra related to water & OH groups are changed.Photoluminescence intensity of all three bands, UV (250 nm), yellow (600 nm) and red (740 nm) strongly diminished and disappeared after heating to 660 C degrees. Radiation induced red luminescence of non-bridging oxygen luminescence center (NBO) appeared in crystal after heat treatment. We had observed a crystalline version of this center (l. Skuja et al, Nuclear Instruments and Methods in Physics Research B 286,159-168 (2012)). Effect of heat treatment explained as sedimentation of phosphorus in some state. Keeping of treated sample at 450-500 C degrees leads to partial revival of ability to create yellow luminescence center under irradiation.

Luminescence of phosphate glasses such as CaO·P2O5 and SrO·P2O5 is compared with that of phosphorus doped crystalline -quartz and phosphosilicate glass with content 3P2O5·7SiO2. Water & OH groups are found by IR spectra in these materials. The spectrum of luminescence contains many bands in the range 1.5 – 5.5 eV. The luminescence bands in UV range at 4.55 eV are similar in those materials. Decay duration in exponential approximation manifests a time constant about 37 ns. Also a component in μs range was detected. PL band of μs component is shifted to low energy with respect to that of ~37 ns component. This shift is about 0.6 eV. It is explained as singlet-triplet splitting of excited state. Below 14 K increase of luminescence kinetics duration in μs range was observed and it was ascribed to zero magnetic field splitting of triplet excited state of the center. Yellow-red luminescence was induced by irradiation in phosphorus doped crystalline -quartz, phosphosilicate glasses. The yellow luminescence contains two bands at 600 and 740 nm. Their decay is similar under 193 nm laser and may be fitted with the first order fractal kinetics or stretched exponent. Thermally stimulated luminescence contains only band at 600 nm. The 248 nm laser excites luminescence at 740 nm according to intra center process with decay time constant about 4 ms at 9 K. Both type of luminescence UV and yellow were ascribed to different defects containing phosphorus. P-doped α-quartz sample heated to 550 co become opalescent. Ir spectra related to water & OH groups are changed. Photoluminescence intensity of all three bands, UV (250 nm), yellow (600 nm) and red (740 nm) strongly diminished and disappeared after heating to 660 C. Radiation induced red luminescence of non-bridging oxygen luminescence center (NBO) appeared in crystal after heat treatment. We had observed a crystalline version of this center (l. Skuja et al, Nuclear Instruments and Methods in Physics Research B 286,159–168 (2012)). Effect of heat treatment explained as sedimentation of phosphorus in some state. Keeping of treated sample at 450-500 C leads to partial revival of ability to create yellow luminescence center under irradiation.

The natures of most radiation-induced point defects in amorphous silicon dioxide ( a -SiO 2 ) are well known on the basis of 56 years of electron spin resonance (ESR) and optical studies of pure and doped silica glass in bulk, thin-film, and fiber-optic forms. Many of the radiation-induced defects intrinsic to pure and B-, Al-, Ge-, and P-doped silicas are at least briefly described here and references are provided to allow the reader to learn still more about these, as well as some of those defects not mentioned. The metastable self-trapped holes (STHs), intrinsic to both doped and undoped silicas, are argued here to be responsible for most transient red/near-IR optical absorption bands induced in low-OH silica-based optical fibers by ionizing radiations at ambient temperatures. However, accelerated testing of a -SiO 2 -based optical devices slated for space applications must take into account the highly supralinear dependence on ionizing-dose-rate of the initial STH creation rate, which if not recognized would lead to false negatives. Fortunately, however, it is possible to permanently reduce the numbers of environmentally or operationally created STHs by long-term preirradiation at relatively low dose rates. Finally, emphasis is placed on the importance and utility of rigorously derived fractal-kinetic formalisms that facilitate reliable extrapolation of radiation-induced optical attenuations in silica-based photonics recorded as functions of dose rate backward into time domains unreachable in practical laboratory times and forward into dose-rate regimes for which there are no present-day laboratory sources.

Fifty years ago, who could have imagined that silicon dioxide—the material of ordinary beach sand—would become one of the most important materials of present-day optics and electronics? Yet SiO2is arguably the most crucial material component in current-generation fiber optics and metal-oxide-semiconductor (MOS) device technology. In MOS field-effect transistors (MOSFETs), SiO2serves not only as the gate insulator, but also as the “field oxide” (which isolates various components of an integrated circuit) and as the packaging material which seals the device from outside contamination. In these roles silica acts as a “perfect dielectric,” being characterized by an essentially infinite resistivity (actually ~1016Ohm · m at 300 K). The ability to form such a high quality dielectric film with a near-perfect lattice match on single-crystal silicon continues to favor silicon-based MOS technology over technologies founded on electrically superior GaAs.In the rapidly developing fiber optic arena, fused silica is still “king” due to a combination of properties, including extremely high transparency over a range of usable wavelengths (Figure 1), low material dispersion (~0 at 1.3/üm), high tensile strength (~ 150 kpsi), and high chemical durability. In addition, bulk forms of silica continue to find application in lenses, prisms, windows, and low-coefficient-of-thermal-expansion reflective optics; thin silica films are common components of the highly reflective and anti-reflective surface coatings which are laid down on reflective and transmissive optics, respectively.

Abstract. The discovery nearly two decades ago of a 90 km-diameter impact crater below the lower Chesapeake Bay has gone unnoted by the general public because to date all published literature on the subject has described it as "buried". To the contrary, evidence is presented here that the so-called "upland deposits" that blanket ∼5000 km2 of the U.S. Middle-Atlantic Coastal Plain (M-ACP) display morphologic, lithologic, and stratigraphic features consistent with their being ejecta from the 35.4 Ma Chesapeake Bay Impact Structure (CBIS) and absolutely inconsistent with the prevailing belief that they are of fluvial origin. Specifically supporting impact origin are the facts that (i) a 95 %-pure iron ore endemic to the upland deposits of southern Maryland, eastern Virginia, and the District of Columbia has previously been proven to be impactoclastic in origin, (ii) this iron ore welds together a small percentage of well-rounded quartzite pebbles and cobbles of the upland deposits into brittle sheets interpretable as "spall plates" created in the interference-zone of the CBIS impact, (iii) the predominantly non-welded upland gravels have long ago been shown to be size sorted with an extreme crater-centric gradient far too large to have been the work of rivers, but well explained as atmospheric size-sorted interference-zone ejecta, (iv) new evidence is provided here that ~60 % of the non-welded quartzite pebbles and cobbles of the (lower lying) gravel member of the upland deposits display planar fractures attributable to interference-zone tensile waves, (v) the (overlying) loam member of the upland deposits is attributable to base-surge-type deposition, (vi) several exotic clasts found in a debris flow topographically below the upland deposits can only be explained as jetting-phase crater ejecta, and (vii) an allogenic granite boulder found among the upland deposits is deduced to have been launched into space and sculpted by hypervelocity air friction during reentry. An idealized calculation of the CBIS ejecta-blanket elevation profile minutes after the impact was carried out founded on well established rules for explosion and impact-generated craters. This profile is shown here to match the volume of the upland deposits ≥170 km from the crater center. Closer to the crater, much of the "postdicted" ejecta blanket has clearly been removed by erosion. Nevertheless the Shirley and fossil-free Bacons Castle Formations, located between the upland deposits and the CBIS interior and veneering the present day surface with units ∼10–20 m deep, are respectively identified as curtain- and excavation-phase ejecta. The neritic-fossil-bearing Calvert Formation external to the crater is deduced to be of Eocene age (as opposed to early Miocene as currently believed), preserved by the armoring effects of the overlying CBIS ejecta composed of the (distal) upland deposits and the (proximal) Bacons Castle Formation. The lithofacies of the in-crater Calvert Formation can only have resulted from inward mass wasting of the postdicted ejecta blanket, vestiges of which (i.e. the Bacons Castle and Shirley Formations) still overlap the crater rim and sag into its interior, consistent with this expectation. Because there appear to be a total of ∼10 000 km2 of CBIS ejecta lying on the present-day surface, future research should center the stratigraphic, lithologic, and petrologic properties of these ejecta versus both radial distance from the crater center (to identify ejecta from different ejection stages) and circumferentially at fixed radial distances (to detect possible anisotropies relating the impact angle and direction of approach of the impactor). The geological units described here may comprise the best preserved, and certainly the most accessible, ejecta blanket of a major crater on the Earth's surface and therefore promise to be a boon to the field of impact geology. As a corollary, a major revision of the current stratigraphic column of the M-ACP will be necessary.

to constitute a volume of non-marine silciclastic materials ∼400 m deep on the continental shelf dated as Lower-Cretaceous. (3) The sediments resting on the present-day Piedmont must be younger still and derived solely from the proto-Blue Ridge, which is presently devoid of the Devonian quartzite identified by Schlee (1957) and others in the upland gravels. The only source of Devonian quartzite available in recent times are accessible solely by the Potomac River in outcrops ∼100 km west of Great Falls, whereas (4) the rest of the streams and rivers on the Middle-Atlantic Coastal Plain originate on the Blue Ridge, which has relatively few quartzite exposures, and those generally date from Cambrian times. Moreover, (5) the ∼5 cubic kilometers of pebbles and cobbles of the upland deposits, which truly blanket the uplands of the Coastal Plane, bear absolutely no relationship to existing streams ... except as possible sources of transportable quartzite. So the mystery is this: How can there be such a huge volume quartzite pebbles and cobbles (with a Devonian component) east of the Blue Ridge? I have argued in Sect. 4.2 that (6) the only way that such copious amounts of Devonian sandstone could be found east of the present-day Blue Ridge requires positing that the Proto-Blue Ridge was once capped by these quartzites in approximately the same manner as the present-day Valley and Ridge Province (immediately to the northwest of the Blue Ridge) is capped by Silurian and Devonian quartzites. (7) The cited studies of Attal and Lavé (2006)* indicate that cobbles of the observed sizes could easily have been transported from the Blue Ridge to the target zone by rivers. Thus, (8) the fact that quartzite gravels of this nature are presently found in a landward annulus between 115 and 200 km from the center of the Chesapeake Bay Impact Structure (CBIS) can be reasonably explained by their (completely possible) original presence within the 400-m-deep non-marine silciclastic materials dated as Lower-Cretaceous identified as being in the target zone of the CBIS impactor (Poag, 1997). *Sorry, this was cited in the text but went missing from my References: Attal, M., and Lavé, J., 2006, Changes of bedload charactistics along the Marsyandi River (central Nepal): implications for understanding hillslope sediment supply, sediment load evolution along fluvial networks, and denudation in active orogenic belts: in Willett, S.D., Hovius, N., Brandon, M.T., and

The natures of most radiation-induced point defects in amorphous silicon dioxide (a-SiO2) are well known on the basis of 55 years of electron spin resonance (ESR) and optical studies of pure and doped silica in bulk, thin-film, and fiberoptic forms. The self-trapped holes (STHs), discovered only in 1989, appear to be responsible for most radiationinduced red/near-IR optical absorption in silica-based photonics. However, accelerated testing of a-SiO2-based devices slated for space applications must take into account the highly supralinear dependence of the initial STH creation rate on ionizing dose rate...and the possibility to permanently reduce the created numbers of STHs by high-dose pre-irradiation.

In 1982, three samples of a model nuclear waste glass, DRG-P1, P2, and P3, were prepared at Pacific Northwest National Laboratory with identical chemical compositions but respectively batched with 0.0, 0.1, and 0.9 wt.% of (PuO2)-Pu-238 ( half life 87.8 years) partially replacing the 1.0 wt.% (PuO2)-Pu-239 (half life 2410 years) present in DRG-P1. In 1999, sub-samples of these three glasses were sent to the Naval Research Laboratory, where electron spin resonance (ESR) was to be used to search for self-irradiation effects due to Pu-238 alpha decay. However, no radiation-induced point defects associated with the aluminoborosilicate network were observed. Rather, profound alpha-decay-induced changes in the ESR spectra of the batched iron-group ions were found. The spectra recorded for DRG-P1 were shown by absolute spin counts to have ESR intensities equivalent to similar to 85% of the sum of the batched 8.28 mol% Fe3+ and 2.79 mol% Mn2+, assuming that all of those ions behave as paramagnetic S=5/2 states at room temperature. (Only 1.7 mol% Ni2+ was batched, and ion-for-ion this S = 1 specie is calculated to contribute only similar to 1/3 of the ESR intensity of an S = 5/2 ion.) Separate experiments and calculations ruled out the possibility of small-particle magnetite-like precipitates comprising even so much as 0.01% of the total iron. A relatively weak ESR spectral feature observed in all three of the DRG-Pn samples at g = 4.3 is the known signature of dilute Fe3+ in glasses. By far the strongest ESR signal was found to be a broad line characterized by a first-derivative zero crossing at g = 2.06 and a peak-to-peak derivative linewidth of similar to 150 mT, both of which are shown to be virtually insensitive to temperature variations in the range 4.2 to 500 K and alpha-decay doses in the range provided by the 17-year aging of the three samples with differing Pu-238 contents. It was discovered that these broad line shapes could be accurately simulated as weighted sums of Lorentzian shape functions of differing widths but having the same g value. The absence of any measurable anisotropy in the broad line, coupled with the temperature invariance of its width, imply the existence of extremely strong exchange interactions within clusters of Fe3+, Fe2+, Mn2+, and Ni2+ ions. The result is a speromagnetic system (amorphous antiferromagnet) characterized by progressive freezing out of like-ion pairs as the temperature is lowered, as opposed to exhibiting a distinct Neel temperature. Calculations that confirm this inference hinge on use of an equation previously derived by one of the authors [D.L. Griscom, V. Beltrain-Lopez, C.I. Merzbacher, and E. Bolden, J. Non-Cryst. Solids 253 (1999) 1 similar to 22) that expresses the ESR intensity of ions behaving as non-interacting paramagnets as a function of their spin S. the spectrometer frequency v, and the temperature T. The most evident ESR effect of 17 years of Pu-238 decay is the (irreversible) lowering of the intensity of the broad line in rough proportion to the amount of Pu-238 in the sample, with associated increases in the amplitude of the narrow g=4.3 feature. It was additionally observed that cooling these glasses gives rise to reversible lowering of the broad-line intensity and increasing of the strength of the g=4.3 feature when compared with theoretical expectation for temperature dependence of non-interacting S = 5/2 paramagnets.The ESR integrated intensityof the broad line as a function of Pu-238 alpha-decay dose proved to be accurately fitted by a simple saturating exponential function asymptotic to zero for infinite-time self irradiation. This result thus promises a precise means of extrapolating thousands of years into the future the process of "super vitrification" resulting from the creation and rapid quenching of "thermal spikes" due to alpha decay in glasses immobilizing Pu-239 or other actinide elements. In addition, because the ESR spectra of several very different candidate high-level nuclear waste (HLW) glass compositions containing even higher amounts of Fe2O3 are also shown here to be decomposable into sums of pure Lorentzians, the analytical method we have devised should be applicable to these and many other HLW glasses containing both iron-group oxides and radionuclides. (C) 2010 Elsevier B.V. All rights reserved.

26-year-old electron spin resonance (ESR) and optical data pertaining to isochronal annealing studies of x-ray induced defect centers in a GeO2-SiO2 glass are revisited here with the object of extracting new insights regarding the fundamental natures of these defects. It is concluded that (i) the paramagnetic Ge(1) and Ge(2) centers are two energetically inequivalent configurations of a single trapped-electron defect, in analogy to what is known to be the case for the Ge(II) and Ge(I) centers respectively in a quartz [Isoya et al., J. Chem. Phys. 69, 4876 (1978)], and (ii) the germanium lone pair center (GLPC) stably traps holes only in pairs and hence remains ESR silent. (C) 2011 Optical Society of America

This paper is a comprehensive review of the state-of-knowledge in the field of radiation effects in glasses that are to be used for the immobilization of high-level nuclear waste and plutonium disposition. The current status and issues in the area of radiation damage processes, defect generation, microstructure development, theoretical methods and experimental methods are reviewed. Questions of fundamental and technological interest that offer opportunities for research are identified.

Some applications of electron spin resonance to the study of amorphous insulators are briefly described. Specific topics addressed include radiation-induced defect centers, redox equilibria, phase separation, photochromics, and ferromagnetic precipitates.

The effects of radiation damage on bulk laser-induced breakdown in SiO2 were investigated. Samples studied included Spectrasil A, B, and WF (water free). Measurements of laser-induced breakdown were conducted with 532 and 1064 nm laser pulses of approximately 20 nsec duration. Reductions of up to 40% in the laser-induced breakdown threshold were observed at 532 nm for samples exposed to 108 rads of γ-radiation. The decrease in breakdown threshold for irradiated SiO2 samples at 532 nm was found to be proportional to the linear absorption of the specimen at 266 nm. These results are in good agreement with a proposed model which suggests that two-photon absorption initiated avalanche process is responsible for laser-induced breakdown for these materials.

This paper reviews half a century of research on radiation-induced point defects in pure and doped glassy silica and its crystalline polymorph α quartz, placing emphasis on trapped-electron centers because the vast majority of all presently known point defects in various forms of SiO2 are of the trapped-hole variety. The experimental technique most discussed here is electron spin resonance (ESR) because it provides the best means of identifying the point defects responsible for the otherwise difficult-to-attribute optical bands. It is emphasized that defects in α quartz have been unambiguously identified by exacting analyses of the angular dependencies of their ESR spectra in terms of the g matrix of the unpaired electron spin and the matrices of this spin's hyperfine interactions with non-zero-nuclear-spin 29Si and 17O nuclides in pure α quartz and/or with substitutional 27Al, 31P, or 73Ge in quartz crystals respectively doped with Al, P, or Ge. Many defects in pure and doped glassy silica can be unambiguously identified by noting the virtual identities of their spin Hamiltonian parameters with those of their far better characterized doppelgangers in α quartz. In fact, the Ge(1) trapped-electron center in irradiated Ge-doped silica glass is shown here to have a crystal-like nature(!), being virtually indistinguishable from the Ge(II) center in Ge-doped α quartz [R.J. McEachern, J.A. Weil, Phys. Rev. B 49 (1994) 6698]. Still, there are other defects occurring in glassy silica that are not found in quartz, and vice versa. Nevertheless, those defects in glasses without quartz analogues can be identified by analogies with chemically similar defects found in one or both polymorphs and/or by comparison with the vast literature of ESR of paramagnetic atoms and small molecules. Oxygen “pseudo vacancies” comprising trigonally coordinated borons paired with trigonally coordinated silicons were proposed to exist in unirradiated B2O3–3SiO2 glasses in order to account for observations of γ-ray-induced trapped-electron-type B- and Si-E′ centers [D.L. Griscom et al., J. Appl. Phys. 47 (1976) 960]. Analogous Al-E′ trapped-electron centers have been elucidated in silica glasses with Al impurities [K.L. Brower, Phys. Rev. B 20 (1979) 1799]). And it has been proposed [D.L. Griscom et al., J. Appl. Phys. 47 (1976) 960] that trapping of a second electron on such oxygen pseudo vacancies accounts for the predominant ESR-silent trapped-electron centers in irradiated silica glasses containing B or Al. The present paper additionally attempts to divine the identities of some of the ESR-silent radiation-induced trapped-electron centers in silica glasses free of foreign network-forming cations. This quest led to the doorstep of the most famous ESR-silent defect of all, the twofold-coordinated silicon, which is found only in silica glasses (not in quartz) and is responsible for the UV/visible optical properties of the oxygen-deficiency center known as ODC(II). The oxygen-deficiency center called ODC(I) is associated with an absorption band at 7.6eV and, though commonly believed to be a simple oxygen mono-vacancy, is clearly more complicated than that [e.g., A.N. Trukhin, J. Non-Cryst. Solids 352 (2006) 3002]. Certain well documented but persistently enigmatic ODC(I)↔ODC(II) “interconversions” [reviewed by L. Skuja, J. Non-Cryst. Solids 239 (1998) 16] have never been explained to universal satisfaction. An innovative combined ESR/thermo-stimulated-luminescence (TSL) study of a series of pure low-OH silica glasses with oxygen deficiencies of 0.000, ~0.015, and ~0.030vol.% [A.N. Trukhin et al., J. Non-Cryst. Solids, 353 (2007) 1560] places new constraints on all future models for ODC(II). Taking this history into account, specific redefinitions of both ODC(I) and ODC(II) are proposed here. The present review also revisits a study of X-ray-induced point defects in an ultra-low-OH, high-chlorine but otherwise ultra-high-purity silica glass [D.L. Griscom, E.J. Friebele, Phys. Rev. B34 (1986) 7524], arguing that (1) most of the reported E′γ and E′δ centers were created via the mechanism of dissociative electron capture at chlorine-decorated oxygen vacancies, (2) the concomitantly created interstitial chloride ions serve as ESR-silent trapped-electron traps, (3) the ESR-detected “Cl0” centers arise from hole trapping on O3≡Si–Cl units without detachment of the resulting Cl atom, and (4) those chlorine atoms that are detached by homolytic bond fission are ESR-silent. Finally, in chlorine-free, low-OH, high-purity silica glasses, up to 100% of the trapped-electron centers appear to be ESR silent and are tentatively ascribed to electron trapping in pairs below the mobility edge of the conduction band. In such cases, the sum of all trapped-hole centers has been found to decay exponentially with increasing isochronal annealing temperature in the range 100 to ~300K [D.L. Griscom, Nucl. Inst. & Methods B46 (1990) 12]. Overall, this review consolidates a large amount of long-existing but often underappreciated knowledge bearing on the natures of trapped-electron centers in pure and doped glassy silica, proposes new models for some of these, and raises a number of questions that cannot be fully answered without future performance of new experiments and/or ab initio calculations.

Silica glass samples doped with extra silicon (SiO2–Si: artificial oxygen deficiency) and with aluminum (SiO2–Al: Al-doped without accompanying alkali ions) were studied. The luminescence properties of these two samples are compared in the range of temperature 15–290K under excitation of ArF excimer laser (193nm). In both samples the luminescence of oxygen deficient centers (ODCs) is detected, i.e., emission bands in the blue at 440nm and the UV at 280nm. Cooling of the both samples led to strong increases of luminescence intensity down to 80K with much smaller increases for still lower temperatures. At 290K in SiO2–Si a luminescence similar to that of twofold-coordinated silicons in stoichiometric silica glasses was detected, i.e., displaying exponential decay of emission bands in the blue (τ=10.3ms) and UV (τ=4.5ns). In both samples emission at 440nm occurs in times shorter that ∼400μs, according to a non-exponential decay law. These decay times are much faster than the 10.3ms exponential decay typical of the twofold-coordinated silicon center in pure undoped silica. Conversely, the decay of the UV band possesses an additional decay ranging from 2 to 5μs, that is much slower than 4.5ns typical of lone twofold-coordinated silicons in stoichiometric silica. Prolongation of the decay time of UV emission can only be explained in terms of electron–hole recombination processes. Moreover, the observed diminishing of the luminescence intensity concomitant with acceleration of decay times with increasing temperature above 90K is found to be correlated with thermally activated recombination of self-trapped holes in pure silica [D.L. Griscom, J. Non-Cryst. Solids 149 (1992) 137]. It is concluded that the ArF-laser induced electronic processes of recombination luminescence in SiO2–Si (and SiO2–Al) are related to trapping of an electron on in a localized state related to oxygen deficiency (or to an Al in the SiO2 network) and nearby trapping of a hole on a normal bridging oxygen, forming an STH.

Photosensitivity of SiO2–Al and SiO2–Na glass samples was probed by means of the induced optical absorption and luminescence as well as by electron spin-resonance (ESR) after irradiation with excimer-laser photons (ArF, 193nm). Permanent visible darkening in the case of SiO2–Al and transient, life time about one hour, visible darkening in the case of SiO2–Na was found under irradiation at 290K. No darkening was observed at 80K for either kind of material. This investigation is dedicated to revealing the electronic processes responsible for photosensitivity at 290 and 80K. The photosensitivity of both materials is related to impurity defects excited directly in the case of SiO2–Na and/or by recapture of self-trapped holes, which become mobile at high temperature in the case of SiO2–Al. Electrons remain trapped on the localized states formed by oxygen deficient defects.

Influences of oxygen-deficiency on radiation properties of high-purity, low-OH fused silica were studied. It is found that thermostimulated luminescence (TSL) peaks are different for photo (7.7eV) and X-ray excitation at 77K. X-ray excitation produces TSL peaks at 125 and 170K corresponding to the anneal temperatures of two types of self-trapped holes centers STH2 and STH1, respectively, detected by electron spin resonance (ESR). Oxygen-deficiency apparently increases the number of electron traps, stabilizing a larger number of STHs in the continuous defect-free silica network than is observed in similarly X-irradiated stoichiometric silica glasses. Photoexcitation of oxygen-deficient glass at 7.7eV produces TSL peaks at 105 and 200K, presently attributed to STHs at perturbed sites in the immediate vicinity of oxygen-deficiency centers (ODCs). High temperature TSL peaks at 240 and 400K are produced by both types of irradiations and are followed by ESR detection of E′ centers only. All observed TSL and ESR signals were proportional to the level of oxygen-deficiency. The main spectral band in TSL near 2.7eV is a triplet–singlet transition, ascribable to the twofold-coordinated silicon center (ODC(II)) modified by its nearest structure. It is proposed that this recombination process results when a thermally detrapped STH encounters an electron trapped at the site of ODC(I), and is transmuted into a modified ODC(II):e−. In principle, any such ODC:e− defect should be paramagnetic. However, no trapped-electron centers were detected by ESR in the present experiments. Based on the recent work of others, the Eα′ centers that were observed are believed to be trapped hole centers. Thus, for reasons unknown, the postulated ODC(II):e− centers, which may be the primary electron traps in oxygen-deficient silicas, appear to be ESR-silent.