Trapped-electron centers in pure and doped glassy silica: A review and synthesis

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