ORIGINAL PAPER Radiation-induced defects in quartz. III. Single-crystal EPR, ENDOR and ESEEM study of a peroxy radical Mark J. Nilges Æ Yuanming Pan Æ Rudolf I. Mashkovtsev Received: 16 May 2008 / Accepted: 4 August 2008 / Published online: 27 August 2008 Ó Springer-Verlag 2008 Abstract The X- and W-band single-crystal electron paramagnetic resonance spectra of an electron-irradiated natural quartz permit quantitative analysis of a 29 Si hyper- fine structure (A *12.6 MHz) and an 27 Al hyperfine structure (A B 0.8 MHz) for a previously reported hole- like center. The 29 Si hyperfine structure arises from inter- action with two equivalent Si atoms and is characterized by the direction of the unique A axis close to a Si–O bond direction. The 27 Al hyperfine structure, confirmed by pulsed electron nuclear double resonance and electron spin echo envelope modulation spectra, is characterized by the unique A axis approximately along a twofold symmetry axis. These 29 Si and 27 Al hyperfine data, together with published the- oretical results on peroxy radicals in SiO 2 as well as our own density functional theory (DFT) calculations on model peroxy centers, suggest this hole-like center to have the unpaired spin on a pair of oxygen atoms linked to two symmetrically equivalent Si atoms and a substitutional Al 3? ion across the c-axis channel, a first peroxy radical in quartz. The nuclear quadrupole matrix P also suggests that the Al 3? ion corresponds closely to the diamagnetic precursor to the [AlO 4 ] 0 center. Keywords Quartz  Electron irradiation  Single-crystal EPR  ENDOR  ESEEM  Hyperfine structures  DFT  Peroxy radical Introduction Peroxy radicals are fundamental oxygen-associated defects in SiO 2 and, along with other defects, exert significant controls on the performance of this important material (Weeks 1956; Friebele et al. 1979; Halliburton et al. 1979; Griscom and Friebele 1981; Edwards and Fowler 1982; Weil 1984; Pacchioni and Ierano ` 1997; Szymanski et al. 2000; Ricci et al. 2001; Kajihara et al. 2005; Kimmel et al. 2007). Particularly, peroxy radicals in SiO 2 are known to be closely associated with radiation processes and have long been proposed to be useful as natural dosimeters and geochronometers for a broad range of applications in anthropology, archeology, mineral exploration and nuclear waste disposal (Garrison et al. 1981; Ikeya 1993; Botis et al. 2005; Pan et al. 2006). Friebele et al. (1979) first established a peroxy radical in neutron or gamma-ray irradiated 17 O-enriched fused silica on the basis of the observed and calculated 17 O hyperfine constants. Friebele et al. (1979) suggested this peroxy radical to derive from preexisting bridging peroxy linkages (:Si–O-O–Si:, where : represents three Si-O bonds), which shed an electron to form peroxy radicals by irradiation and/or thermal treatment. Friebele et al. (1979) showed that the unpaired spin of this peroxy radical has an almost pure p Electronic supplementary material The online version of this article (doi:10.1007/s00269-008-0258-y) contains supplementary material, which is available to authorized users. M. J. Nilges Illinois EPR Research Center, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Y. Pan (&)  R. I. Mashkovtsev Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E2 e-mail: yuanming.pan@usask.ca R. I. Mashkovtsev Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, Novosibirsk 630090, Russia 123 Phys Chem Minerals (2009) 36:61–73 DOI 10.1007/s00269-008-0258-y