Testing the potential of a transferred IRSL (T-IRSL) feldspar signal for luminescence dating

One of the major dilemmas in feldspar luminescence dating is that the infra-red stimulated luminescence (IRSL) signals are either stable and difficult to bleach when measured at elevated temperatures, or unstable and easy to bleach when measured at low temperatures. To identify a signal for sediment dating that is both stable and easy to bleach, we investigate the potential of an optically and thermally transferred IRSL (T-IRSL) signal. Based on the mechanisms described in Wang et al. (2014), we develop a T-IRSL single-aliquot regenerative-dose (SAR) measurement protocol. We investigate the a-thermal stability of six different T-IRSL signals from a sample of infinite age using fading experiments, and by comparing field and laboratory saturation levels. The T-IRSL signal measured at 125 °C (T-IRSL125) following a preheat of 280 °C, is found to be as stable as the post-IR IRSL 290 °C signal (pIRIR290). Furthermore, laboratory bleaching experiments show that the T-IRSL125 signal bleaches faster than the pIRIR290 signal, and that the corresponding residual doses are more than 40% lower. This indicates that T-IRSL signals may be superior to pIRIR methods for dating young and/or insufficiently bleached deposits. However, a SAR protocol performance test of the T-IRSL125 signal yielded a systematic underestimation of 8 ± 2%. This is possibly caused by a sensitivity change during the first preheat and requires further investigation

Bleaching of the post-IR IRSL signal: new insights for feldspar luminescence dating

Post-infrared (pIR) stimulated luminescence dating of sedimentary feldspar largely avoids the effects of anomalous fading that affect conventional infrared stimulated luminescence (IRSL) dating. However, optical resetting of pIR signals is more difficult than resetting the conventional IRSL signal, which may undermine the crucial assumption that pIR signals were effectively bleached upon deposition and burial of sediment grains. In this study, we quantify the bleaching properties of several pIR signals on various samples using laboratory-simulated bleaching in full sunlight and water-attenuated sunlight. Our data show that bleaching is most efficient under full spectrum conditions for all pIR signals and that pIR signals measured at elevated temperature are increasingly harder to bleach than IR and pIR signals measured at low temperature (e.g. IR at 50°C). All bleaching curves exhibit a very slow and steady decrease, indicating that a fixed un-bleachable residual level cannot be reached within the 11 days of solar simulator exposure undertaken here. We show that the magnitude of a laboratory-determined residual dose depends on the adopted bleaching protocol and cannot be used as a proxy for the dose that remains in the sample at the time of burial (remnant dose). Our data emphasize the importance of finding a balance between sufficient signal stability and a minimized contribution of a remnant dose when using pIR procedures for feldspar luminescence dating

Author's personal copy Optically stimulated exoelectron emission processes in quartz: comparison of experiment and theory

a b s t r a c t Recent experiments have demonstrated that it is possible to measure optically stimulated exoelectron emission (OSE) signals simultaneously with optically stimulated luminescence (OSL) from quartz samples. These experiments provide valuable information on the charge movement in quartz grains. Two specific experiments measured the temperature dependence of the OSL and OSE signals on preheat and stimulation temperature. This paper provides a quantitative description of these experiments by using a previously published theoretical model for photostimulated exoelectron emission (PSEE). The experimental data yield a value of w$1.2 eV for the work function of quartz. The experimental temperature dependence of the OSE signals is interpreted on the basis of a photo-thermostimulated (PTSEE) process involving the main OSL trap at$320 1C; this process takes place with a thermal assistance energy estimated at W$(0.2970.02) eV. Good quantitative agreement is obtained between theory and experiment by assuming a thermal broadening of the thermal depletion factor for the OSL traps, described by a Gaussian distribution of energies

OSL-thermochronometry using bedrock quartz: A note of caution

Optically stimulated luminescence (OSL) thermochronometry is an emerging application, whose capability to record sub-Million-year thermal histories is of increasing interest to a growing number of subdisciplines of Quaternary research. However, several recent studies have encountered difficulties both in extraction of OSL signals from bedrock quartz, and in their thermochronometric interpretation, thus highlighting the need for a methodological benchmark. Here, we investigate the characteristic OSL signals from quartz samples across all major types of bedrock and covering a wide range of chemical purities. High ratios of infrared to blue stimulated luminescence (IRSL/BLSL), an insensitive ‘fast’ OSL component, and anomalously short recombination lifetimes seen in time-resolved luminescence (TROSL), are often encountered in quartz from crystalline (magmatic and metamorphic) bedrock, and may hamper successful OSL dating. Furthermore, even when the desirable signal is present, its concentration might be indistinguishable from its environmental steady-state prediction, thus preventing its conversion to a cooling or heating history. We explore the saturation properties and the thermal activation parameters of various OSL signals in quartz to outline the capabilities and limitations for their use in lowtemperature thermochronometry

Luminescence dating, uncertainties and age range

Luminescence ages have an uncertainty of at least 4–5 %, mainly due to systematic errors in both dose rate (conversion factors) and equivalent dose (source calibration) estimation. In most cases, the uncertainty will be higher, due to random errors (e.g., spread in equivalent doses) or uncertainty in assumptions (e.g., water content fluctuations, burial history). Dating is possible for a wide age range of a few decades to about half a million years, although uncertainties are usually relatively large toward the extremes of this range