Thermostimulated luminescence and electron spin resonance in X-ray- and photon-irradiated oxygen-deficient silica A.N. Trukhin a, * , J. Troks a , D.L. Griscom b a Institute of Solid State Physics, University of Latvia, Kengaraga St. 8, LV-1063 Riga, Latvia b ImpactGlass Research International, 3938 E. Grant Road #131, Tucson, AZ 85712, USA Received 23 August 2006; received in revised form 19 January 2007 Available online 21 March 2007 Abstract Influences of oxygen-deficiency on radiation properties of high-purity, low-OH fused silica were studied. It is found that thermosti- mulated luminescence (TSL) peaks are different for photo (7.7 eV) and X-ray excitation at 77 K. X-ray excitation produces TSL peaks at 125 and 170 K corresponding to the anneal temperatures of two types of self-trapped holes centers STH 2 and STH 1 , respectively, detected by electron spin resonance (ESR). Oxygen-deficiency apparently increases the number of electron traps, stabilizing a larger num- ber of STHs in the continuous defect-free silica network than is observed in similarly X-irradiated stoichiometric silica glasses. Photo- excitation of oxygen-deficient glass at 7.7 eV produces TSL peaks at 105 and 200 K, presently attributed to STHs at perturbed sites in the immediate vicinity of oxygen-deficiency centers (ODCs). High temperature TSL peaks at 240 and 400 K are produced by both types of irradiations and are followed by ESR detection of E 0 centers only. All observed TSL and ESR signals were proportional to the level of oxygen-deficiency. The main spectral band in TSL near 2.7 eV 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 E 0 a centers that were observed are believed to be trapped hole centers. Thus, for reasons unknown, the pos- tulated ODC(II):e  centers, which may be the primary electron traps in oxygen-deficient silicas, appear to be ESR-silent. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.80.x; 71.38.Ht; 76.30.Mi; 78.70.g Keywords: Oxidation reduction; Microwave; Radiation effects; Glasses; Optical spectroscopy; Defects; Optical properties; Absorption; Luminescence; Silica; Resonance methods; Electron spin resonance; X-rays 1. Introduction Oxygen-deficiency profoundly affects many properties of silica glass. One of them is the optical absorption in the range of transparency, including two well-known bands at 5 and 7.6 eV (for an in-depth review, see [1]). If the 5 eV absorption band in pure and oxygen-deficient silica is well argued to arise from lone twofold-coordinated sili- con centers [2–4], opinions on the nature of 7.6 eV band are far more divided [5–11]. There is near universal accep- tance that the 7.6 eV band arises from some sort of an ‘oxy- gen-deficiency’ in silica (see [1]), and a case has been made that it is Rydberg-like transition from a Si–Si bonding orbi- tal to a Si 4s state [5–7]. Still, it has been cautioned that the complicated set of experimental data does not allow the 7.6 eV band to be ascribed to such a simple point defect [8,10,11] such as neutral oxygen vacancy. Nevertheless, many workers have shown that photon irradiation at 7.6 eV of silica samples displaying a 7.6 eV absorption band leads to creation of E 0 centers [6,9], as measured by electron spin resonance (ESR), and this result has been 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.01.028 * Corresponding author. Tel.: +371 7 260 686; fax: +371 7 132 7781. E-mail address: truhins@latnet.lv (A.N. Trukhin). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 1560–1566