J. Phys. D: Appl. Phys. 29 (1996) 1047–1050. Printed in the UK Studies of excitation, optical bleaching and thermal annealing of OSL in natural quartz A Shmilevich, M Abu-Rayya, R Chen and N Kristianpoller Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel Received 31 August 1995 Abstract. Optically stimulated luminescence (OSL) was excited at LNT by monochromatic light in x-irradiated natural quartz crystals. Excitation maxima appeared at 290 and 310 nm. The phototransferred thermoluminescence (PTTL) of these crystals showed excitation maxima at the same wavelengths, indicating that carriers are optically stimulated from the same traps. This is supported by the finding that the same wavelengths are most efficient for optical bleaching caused by prolonged illumination. The effects of thermal annealing to gradually increasing temperatures on the OSL were investigated and a correlation to thermoluminescence (TL) peaks was found. The OSL intensities showed sharp decreases after annealing to 160, 190 and 280 K; these temperatures coincide with the temperatures of the main TL glow peaks. It appears therefore that the OSL and the main TL peaks between liquid nitrogen temperature (LNT) and room temperature (RT) are due to the same donor levels. The emission spectrum of the OSL showed that this emission is composed of some bands, which appear also in PTTL as well as in x- and photoluminescence, indicating that the same luminescence centres are responsible for these emissions. 1. Introduction Optically stimulated luminescence (OSL) and its applica- tion to dosimetry and dating have previously been sug- gested by some authors [1, 2]. During recent years this method has frequently been used for the dating of various geological and archaeological materials [e.g. 3, 4]. In this method, samples which have previously been exposed to ionizing radiation are illuminated by light of photoenergies which cannot directly excite luminescence in unirradiated samples. These low-energy photons can, however, stimu- late carriers, which were trapped following ionizing radi- ation. Recombination of the optically stimulated carriers with carriers of opposite sign may result in the emission of OSL. In this respect OSL is similar to phototransferred thermoluminescence (PTTL). The processes of PTTL have been described by many authors [e.g. 5]. Both OSL and PTTL can be excited only in crystals which have previously been exposed to ionizing radiation. The optical stimulation of trapped carriers may result in the emission of OSL or in the transfer of the stimulated carriers from deep to shallower traps, which are stable at low temperature only. PTTL is emitted if, during heating, trapped carriers are thermally released and recombine with carriers of opposite sign at luminescence centres. In a recent study, OSL excited at RT in synthetic quartz has been investigated [6]. In the present work these studies are extended to lower temperatures and to natural quartz crystals. In most previous work OSL was initiated by the powerful radiation of an argon laser at 514.5 nm. For most of our present investigations luminescence was excited by monochromatic light in a broad spectral range and stimulation spectra were measured. For comparison, the low-temperature PTTL and TL of the samples were measured; the effects of optical and thermal bleaching were also studied. In this respect, some recent work on OSL, PTTL and on bleaching effects should be mentioned — the works of McKeever [7], McKeever and Morris [8] and Fain et al [9]. McKeever [7] explains the bleaching as being mainly associated with the loss of recombination centres rather than with the emptying of traps. The light is assumed to empty electrons from deep, thermally disconnected centres only; the freed electrons can then recombine with the trapped holes, thus reducing the number available for TL, and a similar model is given for PTTL results. The effects occurring in OSL and PTTL are numerically simulated from the model by McKeever and Morris [8]. Fain et al [9] utilize a similar model with a large disconnected trapping state for explaining dose dependence and sensitization of TL. These authors further use the notion of partial correlation between TL traps and hole centres for explaining some of the above mentioned experimental results. Finally, some experimental results of bleaching of TL in quartz have been reported by Morris and McKeever 0022-3727/96/041047+04$19.50 c  1996 IOP Publishing Ltd 1047