Infrared Stimulated Luminescence Signal Research Articles

Differential bleaching of quartz and feldspar luminescence signals under high-turbidity conditions

Abstract. Sediment burial dating using optically stimulated luminescence (OSL) is a well-established tool in geochronology. An important but often inapplicable requirement for its successful use is that the OSL signal is sufficiently reset prior to deposition. However, subaqueous bleaching conditions during fluvial transport are vastly understudied; for example the effect of turbidity and sediment mixing on luminescence bleaching rates is only poorly established. The possibility that slow bleaching rates may dominate under certain transport conditions led to the concept that OSL could be used to derive sediment transport histories. The feasibility of this concept is still to be demonstrated, and experimental set-ups are still to be tested. Our contribution to this scientific challenge involves subaquatic bleaching experiments, in which we suspend saturated coastal sand of Miocene age in a circular flume and illuminate it for discrete time intervals with natural light. We record the in situ energy flux density received by the suspended grains in the UV-NIR frequency range by using a broadband spectrometer with a submersible probe. Our analysis includes pre-profiling of each sample following a polymineral multiple signal (PMS) protocol. Using the PMS, the quartz-dominated, blue-stimulated luminescence signal at 125 ∘C (BSL-125) decays slower than the K-feldspar-dominated, infrared-stimulated luminescence signal at 25 ∘C (IR-25) even under subaerial conditions. The BSL-125 from purified quartz shows the opposite behaviour, which renders the PMS unreliable in our case. We find a negative correlation between suspended-sediment concentration and bleaching rate for all the measured signals. For outdoor bleaching experiments we propose to relate the measured luminescence dose to the cumulative received irradiance rather than to the bleaching time. Increases in the sediment concentration lead to a stronger attenuation of the UV–blue compared to the red–NIR wavelength. This attenuation thereby follows an exponential decay that is controlled by the sediment concentration and a wavelength-dependent decay constant, λ. As such λ could potentially be used in numerical models of luminescence signal resetting in turbid suspensions.

Comparison of feldspar dating protocols for loess samples older than 70 ka from the Tianshan Mountains, arid central Asia

Previous studies have demonstrated that quartz optically stimulated luminescence (OSL) dating has limitations for samples older than the last glaciation. However, infrared stimulated luminescence (IRSL) from K-feldspar can be applied beyond this limit if the problem of anomalous fading can be overcome. Elevated temperature stimulated IRSL signals (pIRIR) have shown great potential for minimizing the underestimation. In this study, we compared three commonly applied protocols (pIR50IR290, pIR200IR290, MET-pIRIR) for the same set of loess samples from the Tianshan Mountains in arid central Asia (ACA). For loess samples in the 70–130 ka age range (i.e., De values in the range of 200–400 Gy), pIR200IR290 and MET-pIRIR could both be used for dating, while a varying degree of underestimation occurred for the pIR50IR290 dating protocol. For samples older than 130 ka (i.e., De values in the range of 400–700 Gy), the MET-pIRIR250 signal was the most suitable.

The bleaching limits of IRSL signals at various stimulation temperatures and their potential inference of the pre-burial light exposure duration

Infrared Stimulated Luminescence (IRSL) techniques are being increasingly used for dating sedimentary feldspars in the middle to late Quaternary. By employing several subsequent stimulations at increasing temperatures, a series of post-IR IRSL (pIRIR) signals with different characteristics (stability and bleachability) can be obtained for an individual sample. It has been experimentally demonstrated that higher-temperature pIRIR signals are more stable, but they tend to exhibit larger residual doses up to few tens of Gy, potentially causing severe age overestimation in young samples. In this study we conducted comprehensive bleaching experiments of IRSL and pIRIR signals using a loess sample from China, and demonstrated that non-bleachable components in the IR (and possibly pIRIR) signals do exist. The level of such non-bleachable signal shows clearly positive correlation with preheat/stimulation temperature, which further supports the notion that lower temperature pIRIR are advantageous to date young samples and sediments especially from difficult-to-bleach environments. These results display a potential in constrain the pre-burial light exposure history of sediment utilizing multiple feldspar post-IR IRSL (pIRIR) signals. For the studied loess sample, we infer that prior to its last burial, the sample has received an equivalent of >264 h exposure to the SOL2 simulator (more than 2,000 h of natural daylight).

Testing the accuracy of OSL and pIR IRSL dating of young geoarchaeological sediments in coastal Peru

Luminescence dating of late Quaternary sediments in Peru is challenging, especially on the Peruvian coast. Earlier studies have shown that quartz grains often exhibit a thermally unstable, medium signal that caused the underestimation of Optically Stimulated Luminescence (OSL) ages. InfraRed Stimulated Luminescence (IRSL) dating has shown to produce more reliable ages, depending, amongst other factors, on the age model (Central or Minimum Age Model), and the IRSL signal. IRSL dating of geoarchaeological sediments has, however, hardly been carried out, let along validated, against an independent age dataset. This dating approach is, nonetheless, the only promising way to date the geological substrate in which many of Peru's archaeological sites are buried. Peru contains some of the oldest and most important archaeological heritage sites, yet not much is known of the environmental context in which many of its early civilizations prospered. A better understanding of which luminescence method works best could therefore help in a better understanding of the geological-stratigraphical context of many of Peru's sites. To investigate this matter more fully, we compared the luminescence dating results of seven sediment samples from the top layer of the Lima alluvial fan and from geoarchaeological layers of the Maranga Complex (San Miguel, Lima), with an independent dataset of sixteen 14 C ages. Our results showed that the quartz OSL ages always underestimated the expected ages due to a signal dominated by medium and slow components, and that the post-IR IRSL 225 (pIR IRSL 225 ) and IRSL 50 ages of K-feldspars, on basis of the Central Age Model (CAM), always overestimated the expected ages. The Minimum Age Model (MAM) on the other hand, correctly predicted the expected ages for the early Holocene, Lima alluvial fan sediments using the pIR IRSL 225 signal of K-feldspars, and the late Holocene, geoarchaeological ages using the IRSL 50 signal.

Rock surface luminescence dating of prehistoric rock art from central Iberia

AbstractRock art paintings are notoriously difficult to date numerically. Recently, luminescence dating has been shown to provide reliable rock surface burial ages in various archaeological settings. Here we use the cross‐cutting relationship between a fallen rock and two paintings of the Iberian Levantine (older) and Schematic (younger) styles to constrain the age of the paintings by dating the rockfall event using rock surface luminescence dating. Infrared‐stimulated luminescence (IRSL) signals as a function of depth into the buried face of the talus border indicate that the IRSL signal measured at 50°C (IR50) was sufficiently reset to a depth of about 1.6 mm prior to burial. An uncorrected IR50 age of 1.6 ± 0.2 ka was calculated for the rockfall event by dividing the surface equivalent dose (De) by the total dose rate. This age was corrected using both conventional and field‐to‐laboratory saturation approaches to yield indistinguishable ages of 2.7 ± 0.5 and 2.9 ± 0.3 ka, respectively. Since the panel with Schematic art was first available to the artist after the rockfall, we conclude the Schematic rock art at Villar del Humo is younger than ~2.9 ka. The Levantine rock art was painted on a panel constrained by the talus boulder before detachment, and so it is likely to be older than ~2.9 ka.

Evaluating the effectiveness of heavy liquid density separation in isolating K-feldspar grains using alluvial sediments from the Hajar Mountains, Oman

Heavy liquid density separation is commonly utilised in isolating specific minerals from bulk sediment for luminescence dating. K-feldspars are commonly separated from other minerals by isolating the <2.58 g cm −3 fraction which yields infrared stimulated luminescence (IRSL) signals conducive to dating. However, initial measurements of the IRSL and thermoluminescence (TL) signals from the <2.58 g cm −3 fraction of alluvial fan sediments from the Hajar Mountains, northern Oman, were atypical of K-feldspar luminescence signals reported in the literature. In this study, three different density separates (<2.58 g cm −3 , 2.58–2.54 g cm −3 and <2.565 g cm −3 ) were trialled to attempt to isolate pure K-feldspar samples for dating, to measure K-feldspar IRSL signals which are not contaminated with inputs from other feldspar, quartz and/or heavy mineral signals. The mineralogy of these separates was explored using microscopy, X-ray diffraction and mass spectrometry. We found that despite more refined heavy liquid density separation, the proportions of K-feldspar in these separates had a maximum of 40% by weight, remaining significantly contaminated by other minerals. IRSL and TL signals were atypical of K-feldspar for all density separates and it is likely that there is a contribution of signal from IR-sensitive contaminants, such as muscovite. This highlights the importance of investigating the mineralogy of samples for luminescence dating, especially in regions where little prior work has been undertaken. • K-feldspar fractions remained highly contaminated across the three different density separations applied. • Highlights the need to test the mineralogical purity of samples resulting from standard density separation techniques. • This is particularly important where the signal contributions of IRSL-sensitive contaminants may be relatively greater.

Reconstructing the thermal structure of shallow crust in the Tono region using multi-OSL-thermometry of K-feldspar from deep borehole core

OSL-thermometry can be used to reconstruct the thermal structure in slowly denuded regions where infrared stimulated luminescence (IRSL) signals of samples obtained from deep boreholes are measured and evaluated with depth (e.g., 1.1–2.3 km depth, corresponding to ∼40–75°C; Guralnik et al., 2015a). Until now, only one study has explored this approach, using a target mineral of Na-feldspar. Therefore, in this study, we applied multi-OSL-thermometry to K-feldspar obtained from deep borehole core samples drilled at the Tono region, central Japan, which is a well-documented thermally stable crustal environment. The IRSL signals at 50, 100, 150, and 225°C (IR50, IR100, IR150, and IR225, respectively) were measured. When a combination of four isothermal holding temperatures (ITL) between 190 and 250°C was used for thermal kinetic parameter derivation, the inverted temperatures for the IR50 signals of the samples at a depth of ∼1 km (∼40°C) were most consistent with the in-situ temperature. However, the inverted temperatures for IR100, IR150, and IR225 signals were inconsistent with the in-situ temperatures even though the apparent geothermal gradients estimated from these IR signals are close to the modern geothermal gradient. These results suggest that the application of OSL-thermometry to K-feldspar in a borehole is useful to reconstruct the paleothermal conditions when adopting appropriate thermal kinetic parameters.

Luminescence dating reveals a rapid response to climate change of fluvial terrace formation along the Ani River, northeastern Japan, during the last glacial period

Fluvial terraces along the middle reaches of many Japanese rivers were formed during the last glacial period as a result of changes in sediment discharge related to cooler temperatures and/or reduced water discharge because of lower precipitation. The influence of climate change on these fluvial terraces is not yet fully understood because most previous studies lacked detailed reconstructions of the chronology of terrace development. This study provides a detailed luminescence chronology of fluvial terrace deposits along the Ani River, northeastern Honshu, Japan, and compares that chronology to paleoclimatic records. Eight samples for luminescence dating were obtained from an outcrop of terrace deposits (∼10 m thick) in the Ani River valley. The fading-corrected infrared stimulated luminescence (IRSL) ages are consistent with the fading-corrected post-IR IRSL ages for some samples, which suggests that fading corrections were effective despite the higher fading rates of the IRSL signal. However, for the other samples, the post-IR IRSL ages are significantly older than the fading-corrected IRSL ages due to incomplete bleaching. The pulsed IRSL signals are close to field saturation for older samples, which might have resulted in a greater variation of the ages. Fading-corrected IRSL ages demonstrate periods of rapid aggradation during 105–90 ka and 75–60 ka. Comparison of terrace development with paleoclimatic records indicates that the two periods of fluvial deposition correspond to decreases in precipitation caused by weakened East Asian summer monsoon precipitation and possibly decreases in temperature. The results of this study show that the Ani River responded rapidly to climate change on a time scale of a few tens of thousands of years during the last glacial period.

Luminescence dating of cobbles from Pleistocene fluvial terrace deposits of the Ara River, Japan

Constraining the ages of fluvial terraces is essential to understanding fluvial responses to climate and sea-level changes and estimating uplift/incision. Luminescence dating of sand or silt grains from fluvial terrace deposits in Japan is difficult because sand layers are often absent from gravelly deposits, quartz grains are typically dominated by medium/slow components and/or contaminated by feldspars, and short transport distances and short residence times in riverbeds result in poor bleaching of luminescence signals. Luminescence dating of cobbles may overcome these difficulties, but few studies have applied this technique to fluvial terrace deposits. Here, we examine the utility of luminescence dating applied to three granodiorite cobbles from a late Pleistocene fluvial terrace deposit of the Ara River, Japan. We investigated variations of the infrared stimulated luminescence (IRSL) and post-IR IRSL signals with depth in each cobble. The IRSL and post-IR IRSL signals generally increase with depth, indicating that the cobbles were not completely bleached before deposition. Nonetheless, the IRSL ages of the cobble surfaces (19–17 ka) are consistent with the age of a tephra layer (16–15 ka) at the base of loess deposits overlying the terrace. In contrast, IRSL ages of sand-sized feldspar grains overestimate the depositional age because of incomplete bleaching, whereas silt-sized quartz grains greatly underestimate the depositional age, likely because of the thermal instability of the medium component. Our results demonstrate that luminescence dating of cobbles could provide a better understanding of fluvial systems in which luminescence dating of sand grains is difficult.

Use of infrared light-emitting diodes to determine dosimetric characteristics of MgO:Tb,Gd,Li via the optically stimulated luminescence technique

In this study, the temperature dependence of Infrared Stimulated Luminescence (IRSL) in MgO:Tb,Gd, Li samples were investigated and the basic dosimetric properties were examined for the radiation dosimetry. Terbium, gadolinium, and lithium doped MgO were synthesized using the solution combustion synthesis method, and the characterization of the material was performed by X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The effects of the dopants were investigated by specifying the radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL-blue stimulation/IRSL-infrared stimulation) curves of the MgO:Tb,Gd, Li phosphor. Decay curves of the light flash vs. time showed that the MgO:Tb,Gd, Li was most readily discharged by infrared stimulation. The temperature dependence of the IRSL samples was investigated between 50 and 230 °C. The optimized readout temperature was determined as 120 °C achieving the maximum IRSL intensity. It was shown that there are traps responsible for TL peaks below 200 °C which could be suggested as the source of the IRSL signals for the studied MgO:Tb,Gd, Li samples. The high-temperature TL peak nearly at 400 °C was not affected by infrared stimulation and did not contribute to the obtained IRSL signals. The dosimetric properties such as reusability, multi-readability, dose-response, and fading were examined for applicability to radiation dosimetry. The thermal stability of the sample was investigated using the isothermal annealing technique and activation energy and frequency factor of the traps responsible for IRSL signal were estimated as 0.62 eV and 106 Hz, respectively. The MgO:Tb,Gd, Li luminescent has several properties in its favor. It has been shown that the IRSL signals of the Tb, Gd, and Li doped MgO sample can be investigated and examined as a radiation dosimeter.

First reliable chronology for the Early Khvalynian Caspian Sea transgression in the Lower Volga River valley

During the late Quaternary, dramatic changes in relative sea level (~170 m) are known to have occurred in the Caspian Sea. However, all previous attempts at resolving the uncertainty associated with the timing of these transgressive/regressive events, primarily using radiocarbon, have produced inconclusive or controversial results. Here we present the first reliable chronology for the largest known transgression (Early Khvalynian). This was derived using optically stimulated luminescence (OSL) analysis of sand‐sized quartz, with support from infrared stimulated luminescence (IRSL) from K‐rich feldspar grains, all extracted from 16 sediment samples collected along the Lower Volga River. These samples were taken from loessic sediments, marine clays (known as Chocolate Clays) and the overlying modern soils exposed at three sections (Srednyaya Akhtuba, Raygorod, Leninsk) ~200 km upstream of the present‐day estuary. The differential bleaching rates of the quartz OSL and feldspar IRSL signals were used to evaluate the degree of resetting of quartz (and feldspar) signals; it was possible to conclude that all signals, and particularly quartz OSL, were sufficiently reset at deposition to allow accurate age estimation. Our results show unambiguously that the Early Khvalynian marine Chocolate Clays present at all three sections were deposited post‐LGM, between ~17 and ~13.1 ka ago. These age estimates are further constrained by those from the overlying Kastanozem soils (9.6–0.7 ka) and underlying loess‐soil series (32–19 ka), confirming a young (17–13 ka) age of the transgressive stage of the Early Khvalynian. Relative sea level during this period must have been well above the sampling altitudes of 11.7 m a.s.l. (Srednyaya Akhtuba), 11.3 m a.s.l. (Raygorod) and 4.7 m a.s.l. (Leninsk) to explain the absence of significant alluvial sand and to allow the deposition of the fine Chocolate Clays marker horizon.

Review of the Post-IR IRSL Dating Protocols of K-Feldspar.

Compared to quartz, the infrared stimulated luminescence (IRSL) of K-feldspar saturates at higher dose, which has great potential for extending the dating limit. However, dating applications with K-feldspar has been hampered due to anomalous fading of the IRSL signal. The post-IR IRSL (pIRIR) signal of K-feldspar stimulated at a higher temperature after a prior low-temperature IR stimulation has significantly lower fading rate. Different dating protocols have been proposed with the pIRIR signals and successful dating applications have been made. In this study, we review the development of various pIRIR dating protocols, and compare their performance in estimating the equivalent dose (De). Standard growth curves (SGCs) of the pIRIR signals of K-feldspar are introduced. Single-grain K-feldspar pIRIR dating is presented and the existing problems are discussed.

Correlation between isothermal Tl and Irsl in K-Feldspars of various types

Feldspars are used as natural dosimeters to date geological and archaeological materials. These minerals are widely used in dosimetric methods of dating using luminescence signals, such as Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Infrared Stimulated Luminescence (IRSL). The present work is an effort to compare the Isothermal decay Thermoluminescence signals (ITL) to the IRSL signals from four K-feldspar samples which belong to two different species, namely microcline, and sanidine. The experimental data were fitted by analytical expressions coming from a tunneling recombination model. The results prove that all ITL and IRSL signals can be fitted very accurately with the analytical equations and that only two tunneling components are needed to obtain a high-quality fit. These tunneling components consist of a very fast and intense component, which is followed by an extended slowly decaying component. Significant differences were found between the best-fit parameters of the ITL and IRSL signals, indicating that thermal excitation processes may reach different traps from optical excitation processes in these samples.

Luminescence dating of sediments from central Atacama Desert, northern Chile

Abstract This study examines the feasibility of applying luminescence dating methods to quartz and potassium feldspar (K-feldspar) grains from Quaternary continental deposits of the Mejillones Peninsula and Coastal Cordillera in Central Atacama, northern Chile. Sediment burial ages were calculated using single-aliquot regenerative-dose (SAR) protocols applied to the optically stimulated luminescence (OSL) signal of quartz as well as infrared stimulated luminescence (IRSL) and post-infrared infrared stimulated luminescence (post-IR IRSL) signals of K-feldspar. Considering that the target sedimentary deposits comprise the Late Pleistocene age range, K-feldspar grains were dated using fading-corrected IRSL signals measured at 50 °C (IR50) and post-IR IRSL measured at 225 °C (pIRIR225) to minimize the potential effect of residual doses on calculated ages. The results of the analytical procedures indicate that quartz grains extracted from the studied sediments present a very weak or even no fast OSL component. The combination of a low OSL sensitivity, signal instability and equivalent dose distributions with high overdispersion (>40% for most samples) hinder reliable age estimation using quartz aliquots. Bleaching test results show that the IR50 signal from K-feldspar aliquots is well reset after 20–24 h of light exposure, while the pIRIR225 signal may present residual doses corresponding to between 10 and 15% of the natural signal. IR50 fading rates are ∼6–7%/decade for most studied samples, with exception of one sample which yielded a g-value of 18.77 ± 2.06%/decade. Fading rates for the pIRIR225 signal yielded variable results among sampling sites, with g-values ranging between 0.70 ± 0.24 and 6.77 ± 1.05%/decade. The dating results point out that quartz OSL ages are largely underestimated in relation to K-feldspar fading-corrected IR50 and pIRIR225 ages. Fading-corrected pIRIR225 K-feldspar ages indicate that the alluvial sedimentation in the downthrown block of an active normal fault in Mejillones Peninsula occurred between 163.4 ± 18.4 ka and 87.4 ± 6.6 ka. K-feldspar ages also allow to constrain the age of fault scarp degradation and fault reactivation in two main branches of the Atacama Fault System. In the Naguayan Fault, pIRIR225 ages indicate that faulting occurred after 21.4 ± 3.2 ka while in the Salar del Carmen Fault, faulting is recorded after 14.7 ± 1.0 ka.

Luminescence dating of a transitional Chalcolithic/Bronze Age site in Jordan

In this study, we test the applicability of luminescence dating to geo-archaeological sediments from a “tell” (mound) formation. Combined quartz optically stimulated luminescence (OSL) and K-feldspar infrared-stimulated luminescence (IRSL) dating were applied to eight sediment samples taken from the Tell al-Magass archaeological site in southern Jordan. The site is made up of a sequence of multiple sandy and ash layers covering architectural features of stone and mudbrick. OSL samples were collected from layers previously dated by 14C. Both quartz and alkali feldspars (KF) were measured using, for quartz, blue OSL and, for feldspar, IR50 and pIRIR290 signals. The pIRIR290 signals required the subtraction of residual doses (measured using prolonged stimulation in a daylight simulator); in contrast, the IR50 signals did not include a significant residual dose but did require correction for anomalous fading. The resulting agreement of the ages from the two IRSL signals with those from quartz confirms that the quartz was fully reset before or during the last daylight transport event. This is further confirmed by the satisfactory comparison with previously published 14C dates from the same section. We conclude that luminescence is likely to be very suitable for dating “tell” sediments from this region.

Charge transport in band-tail states of irradiated alkali feldspar I: Super-Arrhenius kinetics

Infra-red stimulated luminescence (IRSL) emission in alkali feldspar comprises two components that arise due to tunneling from the excited state of the primary IRSL trap and the band tail states of the host material. Combination of two Becquerel functions fit well to the IRSL decay curve. The second component which has a longer lifetime was identified with that of the excited state tunneling and found that is dominated at the later part of the decay curve. This part was removed from the IRSL signals to isolate the signals that were predominantly of band tail transport. IRSL decay curves measured at various temperatures from 50 °C to 250 °C after preheated to 280 °C, were fitted to Becquerel function. From the Becquerel function, time-dependent decay rates and the distribution of decay rates were extracted. Ensemble average decay rates were calculated from the distribution of decay rates and found they increase with stimulation temperature. IRSL intensity exhibits a similar behavior. Both were yielding diminishing returns at higher temperatures. Hence, both exhibited a non-linearity in Arrhenius plots. These non-Arrhenius data were analyzed using the deformed exponential function, and that yielded a temperature dependent (decreasing from ∼0.12 eV to ∼ 0.02 eV, with temperature) thermal activation energy. At lower temperature, larger thermal energy is needed to activate the charge transport at lower mobility band tail states, and smaller energy is sufficient at high mobility states. Assuming the processes that are responsible for IRSL intensity change and decay rate change with temperature are different, IRSL intensity change was analyzed using the combination of thermal assistance and thermal quenching. The thermal activation energy of 0.22 eV was obtained for quenching, and it is also observed that the quenching doesn't happen at the recombination center but elsewhere.

Methodological studies on integration time interval's selection for the luminescence ages using quartz and feldspar minerals; sediments collected from Sakarya, Turkey

In this study, two different equivalent dose protocols using Infrared stimulated luminescence (IRSL), namely post IR (pIRIR) and Multi-Elevated temperature post IRSL (MET-pIRIR) were applied to geological samples collected from terrace staircases formed along the Sakarya River, western Anatolia, Eastern Marmara Region, Turkey. Methodological aspects were studied, as the IRSL signal, which is measured at elevated temperatures, yields unusual shape, consisting of an initial increasing part which is followed by the well-known decaying shape. Therefore, according to signal shape, instead of de-convolving the IRSL signals, equivalent dose estimations were performed using different time integration intervals of the emission. The results constitute of two groups, yielding equivalent dose values, in the range between 55 and 110 Gy for selected samples. Since de-convolution of the IRSL signals is both time consuming as well as difficult, mostly due to the presence of tunneling localized transitions, the selection of the appropriate/optimum time integration interval was discussed. The outcomes of this study indicate that IR stimulations at higher temperatures ranging from 200 to 250 °C are useful for feldspar dating, providing that initial increasing part will be eliminated. The thermal activation energy of that unusual part of the signal was calculated around 0.035 ± 0.005 eV using Arrhenius plot, indicating that it may arise from phonon lattice interactions.

Tunnelling recombination in conventional, post-infrared and post-infrared multi-elevated temperature IRSL signals in microcline K-feldspar

In this manuscript, we study three different types of infrared stimulated luminescence signals (IRSL) from a microcline K-feldspar. These signals consist of conventional infrared (IR) stimulation measured at elevated temperatures, multi-elevated temperature post-infrared IRSL signals (MET-pIRIR), and post-infrared IRSL (pIRIR) signals. All three types of signals were analysed using analytical expressions previously derived according to a model based on quantum tunnelling. For the purpose of identifying various tunnelling components, de-convolution analysis was used based on continuous wave infrared stimulation (CW-IRSL), as well as de-convolution based on pseudo linearly modulated transformation of the signals (pLM-IRSL). The variation of the parameters with stimulation temperature was determined using both of these de-convolution methods of analysis. The luminescence curves and normalized signals were investigated at various temperatures using several related protocols. The results of this analysis have implications for the understanding of the emission of luminescence in this material during the above-mentioned protocols, and they highlight the strengths and shortfalls of the tunnelling recombination models. The results from this study contribute to a better understanding of the origin of pIRIR and MET-pIRIR luminescence signals.

Optimization of laboratory illumination in optical dating

Abstract As part of the development of new laboratory lighting, we present a methodological approach applicable to the characterization of any light source intended for illumination in optical dating laboratories. We derive optical absorption cross-sections for quartz and feldspar from published data and compare these with the human eye response. The optimum peak wavelength giving the best clarity for non-dark adapted vision for the least trapped charge loss lies within the wavelength range 590–630 nm; we argue that it is unnecessary to consider dark-adapted vision. The predicted relative decay rates of quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) signals by an incandescent light bulb and a compact fluorescent lamp (CFL) through an ILFORD 902 filter are first derived. These predicted decay rates are then compared with those of three relevant light-emitting diodes (LEDs); this comparison demonstrates the significant advantage of the LED sources over the filtered light sources, because essentially all of the reduction of both OSL and IRSL signals by the LEDs occurs at wavelengths to which the human eye is most sensitive. We conclude that exposure of quartz and feldspar extracts from various samples to the light from an LED with emission peak at 594 nm results in a ≤1% OSL or IRSL signal loss for a 48-h exposure at a power density of ∼0.2 μW.cm −2 .

Influence of the infrared stimulation on the optically stimulated luminescence in four K-feldspar samples

Many dating protocols involve combined measurements of thermoluminescence (TL), optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL). Although the physics behind each stimulation mode is entirely different, it is possible that all of these stimulation modes act on the same set of electron trapping levels existing in dosimetric materials. Therefore, one might expect that the experimental results of the combined TL, OSL and IRSL measurements may be correlated. The present work deals with the correlation between IRSL and OSL signals. The experimental protocol involves an initial exposure of the irradiated sample to infrared radiation (IR) for various stimulation times, and then recording the continuous-wave OSL signal (CW-OSL) of the same sample. In this way one can follow how the exposure to IR influences the trapping levels responsible for the CW-OSL signal. The results of the experiments showed that the IR stimulation influences these trapping levels which are responsible for the fast components of the CW-OSL decay curve, and not the trapping levels responsible for the slow CW-OSL components. The IRSL decay curves are described by analytical equations derived from a localized tunneling recombination model. On the other hand, the CW-OSL decay curves were fitted successfully with either one of two following methods; Firstly they were fitted by using an analytical expression derived from the solution of the one trap one recombination center model (OTOR), which describes delocalized recombination processes. Secondly, the CW-OSL decay curves were also fitted successfully using the same analytical expressions used for fitting the IRSL decay curves, based on localized transition processes. A more detailed analysis of the CW-OSL signals for stimulation durations up to 100s, showed that the description of the CW-OSL using the localized tunneling recombination expression is superior to the description which uses the delocalized OTOR model.