Infrared Stimulated Luminescence Research Articles

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.

Late Quaternary history of the Vakinankaratra volcanic field (central Madagascar): insights from luminescence dating of phreatomagmatic eruption deposits

The Quaternary Vakinankaratra volcanic field in the central Madagascar highlands consists of scoria cones, lava flows, tuff rings, and maars. These volcanic landforms are the result of processes triggered by intracontinental rifting and overlie Precambrian basement or Neogene volcanic rocks. Infrared-stimulated luminescence (IRSL) dating was applied to 13 samples taken from phreatomagmatic eruption deposits in the Antsirabe–Betafo region with the aim of constraining the chronology of the volcanic activity. Establishing such a chronology is important for evaluating volcanic hazards in this densely populated area. Stratigraphic correlations of eruption deposits and IRSL ages suggest at least five phreatomagmatic eruption events in Late Pleistocene times. In the Lake Andraikiba region, two such eruption layers can be clearly distinguished. The older one yields ages between 109 ± 15 and 90 ± 11 ka and is possibly related to an eruption at the Amboniloha volcanic complex to the north. The younger one gives ages between 58 ± 4 and 47 ± 7 ka and is clearly related to the phreatomagmatic eruption that formed Lake Andraikiba. IRSL ages of a similar eruption deposit directly overlying basement laterite in the vicinity of the Fizinana and Ampasamihaiky volcanic complexes yield coherent ages of 68 ± 7 and 65 ± 8 ka. These ages provide the upper age limit for the subsequently developed Iavoko, Antsifotra, and Fizinana scoria cones and their associated lava flows. Two phreatomagmatic deposits, identified near Lake Tritrivakely, yield the youngest IRSL ages in the region, with respective ages of 32 ± 3 and 19 ± 2 ka. The reported K-feldspar IRSL ages are the first recorded numerical ages of phreatomagmatic eruption deposits in Madagascar, and our results confirm the huge potential of this dating approach for reconstructing the volcanic activity of Late Pleistocene to Holocene volcanic provinces.

Dry early Holocene revealed by sand dune accumulation chronology in Bayanbulak Basin (Xinjiang, NW China)

Understanding the Holocene climate changes (especially moisture variation) and their mechanisms in the semiarid–arid Central Asia (SCA) is very important, as water availability is crucial for sustainable developments in this area. This study presents chronostratigraphy of an aeolian sedimentary sequence from Bayanbulak Basin (Xinjiang, NW China), aiming to infer the Holocene moisture history in the SCA. Luminescence dating technique was selected to construct the age framework of the study section. Since the luminescence signal intensity of quartz from the samples was too low to be detected, feldspar was used as an alternative dosimeter. A newly developed post-infrared (IR) IR-stimulated luminescence (IRSL) (pIRIR) dating protocol on K-feldspar was applied to determine the ages of samples. A set of tests on luminescence characteristics was performed and demonstrate that this method is suitable and the resultant ages are reliable. Combined with the stratigraphic investigation on the sand dune/palaeosol section, the results imply a very dry climatic condition characterized by sand dune accumulation at ~9–8 kyr, and a wet interval of 5–1.6 kyr when a soil layer was formed. This moisture variation pattern is consistent with that inferred from many lacustrine records in the SCA, suggesting a widespread dry period at 11–8 kyr. The present results appear to challenge a new stalagmite δ18O sequence, located nearby to Bayanbulak Basin, which instead suggested a humid early Holocene.

Testing a model of alluvial deposition in the Middle Son Valley, Madhya Pradesh, India — IRSL dating of terraced alluvial sediments and implications for archaeological surveys and palaeoclimatic reconstructions

Over the past three decades, the Middle Son Valley, Madhya Pradesh, India has been the focus of archaeological, geological, and palaeoenvironmental investigations that aim to reconstruct regional climate changes in the Late Pleistocene and to understand the effects of the ∼74 ka Toba super-eruption on ecosystems and human populations in northern India. The most recently published model of alluvial deposition for the Middle Son Valley subdivides its alluvium into five stratigraphic formations, each associated with a specific artefact assemblage. In this study, new cross-valley topographic profiles, field observations and infrared stimulated luminescence (IRSL) age estimates are used to refine this model south of the Rehi–Son River confluence. These data not only provide insights into the fluvial history of the Son River and its response to changes in palaeoclimate, but will also inform future archaeological surveys by constraining the geomorphic context of surficial and excavated artefacts in the area.

Small aliquot and single grain IRSL and post-IR IRSL dating of fluvial and alluvial sediments from the Pativilca valley, Peru

Infrared stimulated luminescence (IRSL) and post-IR IRSL are applied to small aliquots and single grains to determine the equivalent dose (De) of eleven alluvial and fluvial sediment samples collected in the Pativilca valley, Central Peru at ca. 10°S latitude. Small aliquot De distributions are rather symmetric and display over-dispersion values between 15 and 46%. Small aliquot g-values range between 4 and 8% per decade for the IRSL and 1 and 2% per decade for the post-IR IRSL signal. The single grain De distributions are highly over-dispersed with some of them skewed to higher doses, implying partial bleaching; this is especially true for the post-IR IRSL. Measurements of a modern analog reveal that residuals due to partial bleaching are present in both the IRSL as well as the post-IR IRSL signal. The g-values of individual grains exhibit a wide range with high individual uncertainties and might contribute significantly to the spread of the single grain De values, at least for the IRSL data. Electron Microprobe Analysis performed on single grains reveal that a varying K-content can be excluded as the origin of over-dispersion. Final ages for the different approaches are calculated using the Central Age Model and the Minimum Age Model (MAM). The samples are grouped into well-beached, potentially well-bleached and partially bleached according to the evaluation of the single grain distributions and the agreement of age estimates between methods. The application of the MAM to the single grain data resulted in consistent age estimates for both the fading corrected IRSL and the post-IR IRSL ages, and suggests that both approaches are suitable for dating these samples.

Geomorphic evidence of recent activity along the Vodice thrust fault in the Ljubljana Basin (Slovenia) – a preliminary study

<p>We investigated two prominent, <strong><sup>~</sup></strong>E-W trending scarps in Quaternary sediments, located close to the town of Vodice in the Ljubljana Basin (central Slovenia). By using detailed geomorphological analysis of the scarps, field surveying, and structural observations of deformed Quaternary sediments, we conclude that the scarps are the surface expression of a N-dipping thrust fault that has been active during the Quaternary. From Optically Stimulated Luminescence and Infrared Stimulated Luminescence dating of deformed Quaternary sediments we estimate a slip rate of 0.1 to 0.3 mm a<sup>-1 </sup>in the last 133 ka. Using the published empirical fault-scaling relationships, we estimate that an earthquake of magnitude 5.9 to 6.5 may be expected on the Vodice thrust fault. The fault may, therefore, present a major seismic hazard for the densely populated and urbanised region of central Slovenia.</p>

Luminescence chronology of the Grub-Kranawetberg site, Austria

Abstract. Das Alter von acht Proben aus einem Lössprofil der Freilandfundstelle Grub-Kranawetberg (Niederösterreich) wurde mittels der Lumineszenzmethoden der IRSL-Datierungen an der polymineralischen Feinkornfraktion und der OSL-Datierungen an der Mittelkornfraktion von Quarzen bestimmt. Kalibrierte Radiokohlenstoffalter von ca. 30 ka für den archäologischen Hauptfundhorizont AH4 werden innerhalb der Fehlergrenzen durch IRSL- und OSL-Alter bestätigt. Anomales Ausheilen der feldspat-dominierten Feinkornfraktion konnte im Labor nicht nachgewiesen werden, weshalb die MAAD-IRSL Alter nicht korrigiert wurden. Während die meisten IRSL- und OSL-Alter innerhalb ihrer Fehlergrenzen übereinstimmen, unterschätzen einige IRSL-Alter die OSL-Alter aus bisher unbekannten Gründen signifikant, wobei die Mittelwerte der OSL-Resultate tendenziell älter als die IRSLDatierungen sind. Nach den OSL-Altern wurde der aufgeschlossene Löss einschließlich eines interstadialen Bodenkomplexes („Stillfried B“) im Zeitraum zwischen ca. 47 ka und ca. 30 ka gebildet. Mögliche edostratigraphische Korrelationen mit einigen europäischen Lössgebieten sowie paläoökologische Überlegungen zur menschlichen Besiedlung im Jungpaläolithikum werden diskutiert.

Single‐Grain Luminescence Dating of Sediment Surrounding a Possible Late Pleistocene Artifact from the Wenas Creek Mammoth Site, Pacific Northwest, USA

Excavations at the Wenas Creek Mammoth Site yielded mammoth, bison, and two possible artifacts in a single colluvial stratum, with radiocarbon bone dates ∼17 ka. Eight infrared‐stimulated luminescence (IRSL) samples were collected to establish general ages of site strata, returning multi‐grain estimates consistent with stratigraphic integrity and the radiocarbon dates. Four additional IRSL samples were collected to estimate the depositional age of one artifact found in place. These produced a pooled total of 94 single‐grain estimates from near the artifact, 80% averaging 16.8 ± 0.9 ka, and 20% averaging 5.1 ± 0.5 ka. These results could be interpreted to demonstrate pre‐Clovis age artifact deposition consistent with the bone dates, or a mid to late Holocene intrusion into older deposits, possibly by bioturbation. The single‐grain IRSL dates do not provide proof of pre‐Clovis presence beyond reasonable doubt at this site, but do show that this technique is valuable in assessing the stratigraphic integrity needed for any such claim.

Luminescence dating of scoria fall and lahar deposits from Somma–Vesuvius, Italy

Luminescence dating has been applied to scoria and lahar deposits from Somma–Vesuvius, Italy. Samples include scoria from the AD472 and 512 (or 536) eruptions and lahar deposits. In order to find a stable luminescence signal which is less affected by anomalous fading, infrared stimulated luminescence (IRSL) signals at elevated temperatures after bleaching with IR at 50 °C (termed post-IR IRSL; pIRIR) were tested at different preheat and elevated stimulation temperatures. The fading rates of both IRSL and pIRIR signals reduced dramatically with increasing preheat and pIRIR stimulation temperatures. A pIRIR signal measured at 290 °C after a preheat at 320 °C (60 s) and an IR stimulation at 50 °C (100 s) was selected to calculate the equivalent dose (De). The gamma spectrometry results indicate that the U-series nuclides are not in equilibrium and there is a large 226Ra excess. The dose rates and ages were calculated by assuming a 226Ra excess (over its parent 230Th) at deposition, and that this unsupported excess then decayed to the present level. The resulting luminescence ages of the two scoria samples agreed with the expected ages, and the ages of the lahar deposits indicate that they are associated with the AD1631 eruption.

Late Quaternary active faulting and landscape evolution in relation to the Gowk Fault in the South Golbaf Basin, S.E. Iran

We present ten infra-red stimulated luminescence (IRSL) ages of feldspar grains within lake-bed sediments and alluvial fan gravels displaced by the Gowk Fault, SE Iran. Our results show that lake deposition in the South Golbaf basin was ongoing from at least 13.5ka (the deepest exposed sediments) until the mid-Holocene. Furthermore, the South Golbaf palaeo-lake is likely to have spilled into the neighbouring Golbaf basin at 6.3±0.2ka. This event led to a widespread incision of the lake-bed and neighbouring alluvial fan surfaces as the drainage systems adjusted to the new base-level. Our constraint on the age of the South Golbaf palaeolake, combined with measurements of 30±5m of right-lateral displacement of stream channels incised into the lake-beds, yields a slip-rate of 3.8–5.7mm/yr. The deposition of alluvial fans around the margins of the South Golbaf depression appears to have largely ended by 12.9±0.7ka. Right-lateral displacements of up to 60m are observed in streams cut into the fan surfaces, yielding a second slip-rate estimate of ~4.4–4.9mm/yr. Much of the widespread incision of the ~12.9ka fan surfaces does not appear to have taken place until ~6ka later, when overtopping of the South Golbaf palaeolake and the adjustment of drainage to a lower base-level, promoted widespread drainage incision.

Combined ESR/U-series chronology of Acheulian hominid-bearing layers at Trinchera Galería site, Atapuerca, Spain

The Sierra de Atapuerca, northern Spain, is known from many prehistoric and palaeontological sites documenting human prehistory in Europe. Three major sites, Gran Dolina, Galería and Sima del Elefante, range in age from the oldest hominin of Western Europe dated to 1.1 to 1.3 Ma (millions of years ago) at Sima del Elefante to c.a. 0.2 Ma on the top of the Galería archaeological sequence. Recently, a chronology based on luminescence methods (Thermoluminescence [TL] and Infrared Stimulated Luminescence [IRSL]) applied to cave sediments was published for the Gran Dolina and Galería sites. The authors proposed for Galería an age of 450 ka (thousands of years ago) for the units lower GIII and GII, suggesting that the human occupation there is younger than the hominid remains of Sima de los Huesos (>530 ka) around 1 km away.In this paper, we present new results obtained by combined Electron Spin Resonance/Uranium-series (ESR/U-series) dating on 20 herbivorous teeth from different levels at the Galería site. They are in agreement with the TL results for the upper part of the stratigraphic sequence (GIV and GIIIb), in the range of between 200 and 250 ka. But for the GIIIa to GIIb levels, the TL ages become abruptly older by 200 ka while ESR ages remain relatively constant. Finally, the TL and ESR data agree in the lowest part of the section (GIIa); both fall in the range of around 350–450 ka. Our results suggest a different interpretation for the GII, GIII and GIV units of Galería and the upper part of Gran Dolina (TD10 and TD11) than obtained by TL. The ESR/U-series results are supported by a Bayesian analysis, which allows a better integration between stratigraphic information and radiometric data.

Dependence of (anomalous) fading of infra-red stimulated luminescence on trap occupancy in feldspars

Dose dependency of anomalous fading of infra-red stimulated luminescence (IRSL) from feldspars has been investigated using radiations of different ionisation qualities. The rate of fading of the IRSL signal after proton irradiation (9.4–30%/decade) is on an average almost twice compared to that after 90Sr/90Y beta particle irradiation (3.5–15%/decade) for all the measured feldspar mineral specimens. Similarly, the fading rates after x-rays of 50kV and 10kV fall in between those of beta particle and proton irradiations. Our results suggest that rate of anomalous fading in feldspars depends on the number density of the trapped charge carriers. These results support the hypothesis that anomalous fading occurs across randomly distributed donor-acceptor distances as opposed to pairs with a fixed distance.

Transport process of sand grains from fluvial to deep marine regions estimated by luminescence of feldspar: example from theKumano area, centralJapan

AbstractUsing the concept of bleaching in optical dating, a new index of sediment sample bleaching percentage (BLP‐2) was developed and applied to evaluate sand grain transport from riverine to deep‐marine environments. As bleached grains in modern sediments have no optically stimulated luminescence (OSL)/infrared stimulated luminescence (IRSL) signal, bleached and unbleached feldspar grains are distinguished byIRSLintensity. TheBLP‐2 distribution of present deposits around theKumano area, on thePacific coast of centralJapan, suggests that sand grains in surface turbidites obtained from the bottom of theKumanoTrough are of flood/storm origin rather than seismogenic origin. The distribution ofBLP‐2 tentatively suggests sand grain erosion–transport–depositional processes; for example, origin and transport agencies of shelf sand, and influence of coastal erosion on the beach deposit. Although the presentBLPanalysis is not yet supported by a rigorous statistical test, it is useful to distinguish recent deposition and remobilization of sand grains. Furthermore, if the depositional age and the luminescence age of sand grains are accurately estimated, sand grain transport processes of old (lateQuaternary) sediments may be estimated by the methodology similar to that of the present study.

On the dose dependency of the bleachable and non-bleachable components of IRSL from K-feldspar: Improved procedures for luminescence dating of Quaternary sediments

The infrared (IR) stimulated luminescence (IRSL) and post-IR IRSL (pIRIR) signals from K-feldspar can, for convenience, be divided into two components, bleachable and ‘non-bleachable’, where the latter corresponds to the ‘residual’ signal observed in sunlight-bleached samples. In this paper, we examine the non-bleachable component of IRSL of K-feldspar for several sedimentary samples from across Eurasia. We observed a large variability in the residual doses among these samples after prolonged exposure to sunlight. By employing multiple elevated temperature (MET) IR stimulations at 50–300 °C, we show that the residual dose increases systematically with stimulation temperature, attaining values as high as ∼50 Gy at 300 °C, even after several hours to tens of hours of exposure to unfiltered sunlight. We examined two samples in detail and found that the bleachable and non-bleachable components produced different dose response curves. Pulse annealing studies showed that the non-bleachable component is more stable than the bleachable component, suggesting that a preheat procedure cannot eliminate the non-bleachable component. Additional experiments revealed that the non-bleachable component is dose dependent. Owing to this dose dependency, we demonstrate mathematically and empirically that the simple subtraction of a residual dose from the measured equivalent dose (De) – which is the most common approach employed (if any residual dose is subtracted at all) – will result in underestimation of the actual De. We present a method to correct for the dose dependency of the residual dose, which can improve the accuracy of either MET-pIRIR or pIRIR age estimates for samples in which the non-bleachable component represents a significant fraction of the measured signals.

Potential and limits of OSL, TT-OSL, IRSL and pIRIR<sub>290</sub> dating methods applied on a Middle Pleistocene sediment record of Lake El'gygytgyn, Russia

Abstract. This study tests the paleomagnetic and proxy-data based Mid- to Upper Pleistocene sediment deposition history of Lake El'gygytgyn by applying different approaches of luminescence dating techniques on sediment cores taken from the centre of the 175 m deep lake. For dating polymineral and quartz fine grains (4–11 μm grain size range) were extracted from nine different levels from the upper 28 m of sediment cores 5011-1A and 5011-1B. According to the independent age model, the lowest sample from 27.8–27.9 m below lake bottom level correlates to the Brunhes-Matuyama (B/M) reversal. Polymineral sub-samples were analysed by infra-red stimulated luminescence (IRSL) and post-IR IRSL measured at 290 °C (pIRIR290) using single aliquot regenerative dose (SAR) sequences. SAR protocols were further applied to measure the blue light optically stimulated luminescence (OSL) and thermally-transferred OSL (TT-OSL) of fine-grained quartz supplemented by a multiple aliquot approach. Neither low temperature IRSL measurements at 50 °C nor any OSL dating approach on quartz yielded reliable results. Deconvolution of their dose response curves revealed a pseudo-increase of the dose response curves and explains the observed underestimation. The pIRIR protocol applied to polymineral fine grains was the only luminescence technique able to provide dating results of acceptable accuracy up to ca. 700 ka when correlated to the existing proxy-data and paleomagnetic based age record. We present the potential and limits of the different dating techniques and a correlation of pIRIR290 results with the proxy-data based age model.

Extending the age limit of luminescence dating using the dose-dependent sensitivity of MET-pIRIR signals from K-feldspar

We investigated the sensitivity change of multiple-elevated-temperature (MET) stimulated post-infrared infrared-stimulated luminescence (MET-pIRIR) signals as a response to irradiation, sunlight bleaching and heating using samples from the Mu Us Desert, central China. A strong dose dependence of MET-pIRIR signal sensitivity was observed. The intensity of the test-dose signals (Tx) increase with the pre-dose received. Furthermore, the signal sensitivity can be reset by sunlight bleaching or heating. This suggests that both the electron traps and hole centres in K-feldspar can be bleached by sunlight, and can, therefore, be used for dating. Using the test-dose signal as a monitor for sensitivity change, it was found that the sensitivity (or hole centres) saturate at a higher dose (D0 = ∼750 Gy) than the sensitivity-corrected signals (or electron traps) (D0 = ∼400 Gy). We propose a multi-aliquot regenerative-dose (MAR) MET-pIRIR dating protocol, which utilises the high saturation dose of hole centres. This protocol was tested using aeolian sediments from north China with ages ranging from 0 to 470 ka. It was found that, compared to the dose limit of ∼800–1000 Gy using the normal MET-pIRIR or pIRIR procedure, the new method can measure a natural dose of up to ∼1500 Gy and produce ages consistent with the expected ages for the samples investigated.

Luminescence (IRSL) dating of Yeni Rabat church in Artvin, Turkey

Luminescence dating is a chronological method that has been used extensively in terrestrial materials. In this study, we present Infrared Stimulated Luminescence (IRSL) dating results obtained for sediment and pottery samples taken from Yeni Rabat Church, Ardanuç, Artvin, Turkey. For this purpose, equivalent dose (ED) and annual dose rate (AD) of samples were measured. For annual dose rate, concentrations of radioactive isotopes (U, Th, K) were determined by using a high-purity germanium detector. For the equivalent dose, polymineral fine grain SAR (Single Aliquot Regenerative Dose) and MAAD (Multiple Aliquot Additive Dose) procedures were used. The optimal preheat temperature was determined for sediment and pottery samples. Ages were calculated by Aitken's luminescence age calculation method, which found 710±190 years for the pottery sample and 1450±370 years, 1390±420 years, 1430±310 years, 2210±520 years and 1640±390 years for different sediment samples, respectively. These estimated age ranges support the theory that Yeni Rabat Church could have been constructed in medieval times.

Na-rich feldspar as a luminescence dosimeter in infrared stimulated luminescence (IRSL) dating

Abstract One of the challenges in dating rock surfaces is the choice of the luminescence mineral. Although quartz is the preferred dosimeter in sediment dating, it is often not sufficiently sensitive when extracted from solid rocks. The intensity of signals from feldspars tends to be much less dependent on geological origin and erosion history, but the dosimetry of K-rich feldspar grains extracted from rocks is complicated because the internal dose rate is very dependent on the original feldspar grain size. The in situ grain size information is lost during the crushing process used to separate the grains for measurement. This latter problem does not apply to Na-rich feldspar because of the absence of internal radioactivity. The potential application of Na-rich feldspar as a luminescence dosimeter for the IRSL dating of rock surfaces is investigated using a variety of sediment samples from different geological settings for which independent age control is available. The blue and yellow luminescence emissions are measured for IR stimulation at 50 °C (IR 50 ), and post-IR IR stimulation at 290 °C (pIRIR 290 ). Thermal stability experiments imply that the corresponding signals in both emissions have comparable thermal stabilities and that all signals have similar recombination kinetics and are thermally stable over geological timescales. The IR 50 doses measured using blue and yellow emissions are similar to or lower than quartz doses while pIRIR 290 blue doses are higher than those from yellow emission and quartz doses. The fading rates measured for the IR 50 signals are ∼3%/decade larger than those measured for the pIRIR 290 signals in both yellow and blue emissions. Furthermore the average fading rates of both yellow signals are ∼3%/decade higher than the corresponding fading rates of the blue signals. However, there is no detectable correlation between fading rates and the measured D e values. The residual doses measured from the laboratory-bleached samples and a modern analogue suggest that the IR 50 signals in both blue and yellow emissions bleach to the same degree, as do the corresponding pIRIR 290 signals, and that there is no significant naturally-unbleachable residual dose observed using these signals. Neither anomalous fading nor incomplete bleaching explains the observed dose discrepancy between the two emissions. Eight uncorrected and fading-corrected ages are calculated for each sample based on all four signals, using the dose rate relevant to Na-rich feldspar extracts (i.e. ∼3% K). The IR 50 and pIRIR 290 blue ages were also calculated assuming a dose rate based on 12.5% internal K (i.e. assuming that the blue signals were mainly derived from contamination by K-rich feldspar). The latter pIRIR 290 blue ages are in agreement with the expected age control, raising the possibility that this signal originates mainly from K-rich feldspar contamination in our Na-rich fractions, and thus is not so useful in the luminescence dating of rock surfaces. On the other hand, the pIRIR 290 fading-corrected ages based on the yellow emission are consistent with the independent age controls; higher preheat and stimulation temperatures may result in more stable yellow signals from Na-rich feldspar extracts from rocks, and so reduce the size of the fading correction. We conclude that, because this signal avoids the dosimetry difficulties of K-rich feldspar extracts, it has considerable potential in the IRSL dating of rock surfaces.

Analytical solutions for stimulated luminescence emission from tunneling recombination in random distributions of defects

Recently a new kinetic model was presented in the literature, which describes localized electronic recombination in donor–acceptor pairs of luminescent materials. Within this model, recombination is assumed to take place via the excited state of the donor, and nearest-neighbor recombinations take place within a random distribution of centers. Two versions of the model were presented which were found to be in good agreement with each other, namely an exact model that evolves both in space and in time, and an approximate semi-analytical model evolving only in time. The model simulated successfully both thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL), and also demonstrated the power law behavior for simulated OSL signals. This paper shows that the system of simultaneous differential equations in the semi-analytical model can be approximated to an excellent precision by a single differential equation. Furthermore, analytical solutions are obtained for this single differential equation, and for four different experimental modes of stimulation: TL, OSL, linearly modulated OSL (LM-OSL) and isothermal TL processes. The exact form of the power law for the model is found in analytical form for both OSL and isothermal TL processes. The analytical equations are tested by successfully fitting typical infrared stimulated luminescence (IRSL) signals, as well as experimental TL glow curves from feldspar samples. The dimensionless number density of acceptors in the model is estimated from fitting the experimental IRSL and TL data. The analytical expressions derived in this paper apply also to stimulated emission via the excited state of the donor–acceptor system. However, the same analytical expression, with different numerical values for its constants, can also be applied in the case of ground state tunneling, with important implications for luminescence dating.

The effect of band-tail states on the thermal stability of the infrared stimulated luminescence from K-feldspar

The thermal stability of the infrared stimulated luminescence (IRSL) signal from a sedimentary K-feldspar was investigated using isothermal decay study. It is observed that the isothermal decay of IRSL signal cannot be described using a first-order exponential decay function. Instead, the decay can be well described by considering the presence of band-tail states. Based on the isothermal decay results, a trap depth of ∼1.92eV was obtained for the IRSL stimulated at 50°C and the width of the band-tail states was found to be ∼0.37eV below the conduction band edge. Deeper trap depths (up to ∼2.06eV) were obtained for multi-elevated-temperature post-IR IRSL (MET-pIRIR) at elevated temperatures. Based on these observations, the implication for the IRSL dating feldspar was discussed.