IR Stimulation Research Articles

Conventional IRSL dating of Romanian loess using single aliquots of polymineral fine grains

Abstract Investigations of the luminescence characteristics of polymineral fine grains extracted from the loess-palaeosol sequence near Mircea Voda (SE Romania) were performed using IR stimulation at 50 °C in a single-aliquot regenerative-dose (SAR) protocol. Initial sensitivity changes were observed to influence the ability to measure a given dose. They are shown to depend on preheat temperature, bleaching procedure and size of the given dose. An apparent influence of the preheat temperature on equivalent dose and fading corrected ages is documented through thermal stability experiments. These suggest that, in the absence of a sufficiently high preheat treatment, thermally unstable components contribute to the IRSL signal leading to significant age underestimation. When a high preheat temperature is used (250 °C for 60 s), the age results are in good agreement with previously obtained quartz-OSL ages for material deposited during the last glacial period. However, this agreement may be caused by initial sensitivity changes and limitations of the fading correction.

New chronostratigraphic results for Lower Austrian loess/palaeosol sequences

It has been shown that the infrared stimulated luminescence signals measured at elevated temperature after an IR stimulation at 50 °C (post-IR IRSL) are significantly more stable than the conventional IRSL at 50 °C (IR50). In this study a post-IR IRSL protocol using a second IR stimulation temperature of 290 °C (pIRIR290) was applied to 17 polymineral fine grain (4–11 μm) samples from various loess sections in the Eifel region (Wannenköpfe, Dachsbusch, Kärlich and Ariendorf) with independent age control to test the reliability of ages using the pIRIR290 signal. The laboratory-measured fading rates are below 1%/decade on average for the pIRIR290. Both IR50 and pIRIR290 signals of 9 samples were found to be in field saturation. The average ratio of the sensitivity-corrected natural signal to the laboratory saturation level for the pIRIR290 is 0.98 ± 0.02 (n = 9), showing that field saturation is equal to laboratory saturation for the pIRIR290 signal from polymineral fine grains from the Eifel region. Minimum equivalent dose estimates were calculated from the characteristic saturation dose of the dose response curves, giving minimum ages estimates of ∼230–420 ka, and suggesting that the pIRIR290 signal can be used to date loess to ∼300 ka. The pIRIR290 ages estimates of the samples from the Wannenköpfe and Dachsbusch sites are in good agreement with independent age control showing that the IRSL dating using pIRIR290 signal without fading correction is apparently reliable. Our data suggest that the loess units E, F, G and the lower part of H at the Kärlich site were accumulated >270 ka and that the palaeosol of the Kärlich Interglacial I most likely developed during marine isotope stage (MIS 9) or earlier. The pedocomplex on the top of Loess bed II at the Ariendorf section can be correlated with MIS 7.

Deregulation of Specific Sets of Genes Detected by Microarray Analysis of Marrow Stromal Fibroblast Cells Stimulated by IR and VR Light

Conflicting reports have questioned whether low level laser treatment can have an effect on bone. Purpose:The purpose of this study was to examine how light affects gene expression. Methods: Clones of marrow fibroblast stem cells were isolated from human bone marrow and used for primary cell cultures. The cells were grown without light as a control and with light under eight different conditions: two wavelengths of light(830-IR and 633nmVR) at four different energy levels(0.5.1.0,1.5 and 2.0 joules /cm2). Results: Light stimulated some cultures to proliferate up to 40% faster depending on the type of light stimulation using BrdU markers. For the light-stimulated cultures, western blot data for osteocalcin, alkaline phosphatase and RUNX 2, markers of osteoblast differentiation and bone formation, did not show a pattern of increased or early gene expression compared to control cultures. Affymetrix Human exon microarrays of 22,000 protein-encoding genes (40 markers per gene) showed distinct sets of genes being deregulated for each of the eight experimental conditions. A two-fold screen for gene expression differences between control and light-stimulated cultures revealed a complex network of gene expression interactions involving dose response and silencing of inhibitor genes for candidate genes such as RANKL, IL-1A and MMP10. Pathway analysis showed the top VR biological gene networks were skeletal and muscular system development and function, tissue development and amino acid metabolism, consistent with bone turnover. The top biological functions associated with IR stimulation are skin condition, genetic disorders, cancer, immune response. Conclusion: This study provides strong evidence for light stimulating different sets of genes according to wavelength and energy level that can alter bone turnover. The data provides a molecular explanation for the conflicting reports in the current literature.

Luminescence dating of fluvial deposits in Vojvodina, N Serbia: First results

This paper reports on the first investigations into the potential of luminescence dating to establish a chronological framework for fluvial processes in the Tisa River Valley in Vojvodina, N Serbia. A total of 18 samples were collected from a terrace exposure near Mužlja, which comprised non-fluvial deposits at the top and fluvial deposits at the base. The luminescence characteristics of sand-sized quartz and potassium feldspar grains were investigated using a single-aliquot regenerative dose (SAR) protocol. The quartz separates exhibit a complex behaviour, making this dosimeter less suited for optical dating. Investigations into the behaviour of infrared stimulated luminescence (IRSL) measured at 50 °C (IR50) from K-rich feldspar extracts showed that preheating in excess of 60 s at 225 °C leads to significant sensitivity changes. The effect of IR stimulation on the thermoluminescence (TL) signal and that of preheating on IRSL intensity were examined; the results are inconclusive with respect to thermal stability, but are not inconsistent with the idea that the data do not reflect depletion of an electron trap. The IR50-signal measured after a preheat of 60 s at 115 °C behaves well in the SAR protocol, although it suffers from anomalous fading. Assuming that the signal is thermally stable, the fading-corrected ages suggest that deposition occurred during the end of the Late Pleniglacial and the early Late Glacial, which is consistent with geological expectations. Our observations demonstrate that IRSL dating of feldspar holds potential for establishing a chronology of fluvial dynamics of the Tisa River in N Serbia. Further methodological investigations are desirable; however, as issues relating to the stability and resetting of the IRSL signal remain to be resolved.

Validating post IR-IRSL dating on K-feldspars through comparison with quartz OSL ages

Recent developments have opened up the possibilities of using potassium feldspar for dating Pleistocene sediments; a stable (less-fading) part of the infrared stimulated luminescence (IRSL) signal can be selected by largely depleting the unstable part of the IR signal, using a combination of thermal and IR stimulation: post IR-IRSL dating (pIR-IRSL).This study aims to test the validity of pIR-IRSL dating on feldspars. We obtained pIR-IRSL ages on a large suite of samples from several locations in the Netherlands area, covering a wide range of depositional environments and ages. Age control was provided by quartz optically stimulated luminescence (OSL) ages on the same samples; these ages were shown to accord with geological age constraints. Comparison with IRSL ages enabled us to evaluate the improvement that pIR-IRSL dating provides over conventional IRSL methods.The majority of feldspar ages obtained with pIR-IRSL showed good agreement with both the quartz OSL ages and the geological age constraints. Our study demonstrates that pIR-IRSL dating is more robust than conventional IRSL and should be the method of choice in feldspar luminescence dating of Pleistocene sediments.

Effects of thermal treatments on luminescence features of three natural feldspars

Abstract The effects of prior infrared stimulation on the TL emission of three feldspar minerals (albite, sanidine and orthoclase) were studied. Different reductions in the TL signal were observed in the three samples: albite (Na-rich feldspar) was only partially affected by stimulation while there was an important decrease of TL signal in sanidine and orthoclase (K-rich and intermediate K–Na feldspars). A similar behaviour was also detected when the samples were illuminated at different temperatures. Moreover, when the IR stimulation was performed at temperatures below 100 °C, there was a charge transfer effect (PTTL) that progressively rose, moving from albite to sanidine to orthoclase. A dose recovery experiment was also performed, varying both preheat and measurement temperature. Our results are a further confirmation of the complexity and variability of the luminescence processes in feldspars. They also indicate that the luminescence characteristics of the albite we dealt with are particularly useful for dosimetric application.

Testing Post-IR IRSL protocols for minimising fading in feldspars, using Alaskan loess with independent chronological control

Abstract Concern over anomalous fading has been the biggest single factor responsible for deterring the widespread use of the infra-red stimulated luminescence (IRSL) or thermoluminescence (TL) signal from feldspars for luminescence dating. There has therefore been great interest in the use of the recently proposed Post-IR IRSL signal, because it has been shown to significantly reduce the degree of anomalous fading observed in feldspars and therefore potentially provides a means of circumventing the issue. This study undertakes a systematic investigation into various preheat and Post-IR IRSL measurement conditions proposed in the literature, by using two samples from the Halfway House loess section in Alaska which bracket the Old Crow tephra which has been dated using fission track methods. Preheat plateau tests show a dramatic change in equivalent dose with Post-IR IRSL measurement conditions, and further tests reveal that these changes are driven by preheat temperature rather than Post-IR IR stimulation temperature. Dose recovery tests on laboratory-bleached material mimic the findings of the natural preheat plateau test data, and sensitivity change between the first and second Single Aliquot Regenerative dose (SAR) measurement cycle is found to be responsible. Comparison of the Post-IR IRSL ages with the independent age control shows that, for the samples in this study, the Post-IR IR signal stimulated at 290 °C is inappropriate for dating. However, use of lower preheat (250–300 °C) and Post-IR IR stimulation temperatures from 225 to 270 °C gave rise to ages which were in agreement with the independent age control.

Natural variations in the properties of TL and IRSL emissions from metamorphic and volcanic K-feldspars from East Africa: Assessing their reliability for dating

Abstract The elevated temperature infrared stimulated luminescence (IRSL) and post-IR IRSL signals of potassium (K)-feldspars have recently garnered attention for their minimal rates of anomalous fading. The post-IR IRSL signal has been used to obtain age estimates for geological deposits, mostly in Europe. Studies on the behaviour of the IRSL and post-IR IRSL signals of K-feldspars from a wider range of geographic regions and depositional contexts are needed, particularly for regions where the OSL signal from quartz is poorly behaved. Discrepancies in the literature regarding the behaviours of the IRSL and TL signals of K-feldspars also highlight the need to characterise the behaviours of samples from a wide variety of contexts. This paper begins to address this problem by characterising and comparing the IRSL signals of a metamorphic and a volcanic K-feldspar sample from two sites in East Africa, a region in which the OSL signal from quartz has generally proven problematic for dating. We demonstrate that the metamorphic and volcanic K-feldspars have substantially different TL glow curves that respond differently to IR stimulation. The sample of metamorphic K-feldspar from Tanzania (MR9) has a peak at 430 °C that is associated with the IRSL signal and an optically less-sensitive peak at 350 °C, while the sample of volcanic K-feldspar from Ethiopia (MB3) exhibits a single broad TL region centred at ∼230 °C that responds differently to IR stimulation. Differences in the change of IRSL decay curve shape with stimulation temperature suggest that the processes of IRSL production many vary between the two samples. Using dose recovery tests, we demonstrate that the IRSL (50 °C), IRSL (225 °C) and post-IR IRSL (50 °C, 225 °C) signals of sample MR9 are suitable for dose and age estimation using the single-aliquot regenerative-dose procedure, while those of sample MB3 are less suitable. The post-IR IRSL signal of the latter sample performs poorly in tests of SAR suitability and the three signals exhibit extremely high fading rates over laboratory timescales (g 2days > 19%/decade).

Testing the potential of elevated temperature post-IR IRSL signals for dating Romanian loess

In this study we test the potential of the elevated temperature infrared stimulated luminescence (IRSL) signals for dating Romanian loess. The recently developed post-IR IRSL protocol is applied to Romanian loess using polymineral fine grains extracted from the loess-palaeosol sequence at Mircea Vodă (SE Romania). This approach is aimed at obtaining an additional age control to examine the age discrepancy obtained from previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11 μm and 63–90 μm).Two preheat post-IR IR stimulation temperature combinations were used, 250–225 °C and 325–300 °C, respectively. The signals obtained are documented in terms of dose response curve, laboratory tests and fading. Although both post-IR IRSL signals exhibit small fading rates, dose response characteristics indicate that these rates may be laboratory artefacts. The post-IR IRSL signal stimulated at 300 °C is observed to suffer from dose dependent initial sensitivity changes as both natural and regenerated signals are observed to lie above the saturation level of the dose response curve. Uncorrected age results obtained using both post-IR IRSL signals are in general agreement with previously reported silt-sized quartz OSL ages for samples collected from the uppermost loess unit L1. For older material, the post-IR IRSL signal stimulated at 225 °C is considered to provide reliable age results, in agreement with independent age control available for this sequence.

Effects of thermally transferred signals in the post-IR IRSL SAR protocol

Abstract The recently developed post-IR IRSL SAR protocol is promising to isolate more stable IRSL signals of feldspars. However, the high temperature thermal treatments used will inevitably induce thermally transferred post-IR IRSL295 (TT-post-IR IRSL295) signal, which would contribute to the measured post-IR IRSL295 signal of the test dose and may lead to inaccurate sensitivity correction. In this study, the effects of TT-post-IR IRSL295 signal in the post-IR IRSL295 SAR protocol are investigated using medium polyminerals from a loess section at Caoxian, northwestern Loess Plateau in China. The sensitivity changes of the IRSL50 and the post-IR IRSL295 signals are different from natural cycle to regenerative cycles, which can be attributed to the interference of the TT-post-IR IRSL295 signal. Such difference is dependent on the test dose and the post-IR IR stimulation time. The TT-post-IR IRSL295 signal is also shown to affect the post-IR IRSL295 Do and De values and to cause overestimation of the fading rates. Our study therefore highlights the need of serious consideration on the effects of TT-post-IR IRSL signal when the post-IR IRSL SAR protocol is employed for dating.

On the applicability of post-IR IRSL dating to Japanese loess

Recent work on infrared stimulated luminescence (IRSL) dating has focussed on finding and testing signals which show less or negligible fading. IRSL signals measured at elevated temperature following IR stimulation at 50°C (post-IR IRSL) have been shown to be much more stable than the low temperature IRSL signal and seem to have considerable potential for dating. For Early Pleistocene samples of both European and Chinese loess natural post-IR IRSL signals lying in the saturation region of the laboratory dose response curve have been observed; this suggests that there is no significant fading in nature. As a contribution to the further testing of post-IR IRSL dating, we have used 18 samples from two Japanese loess profiles for which quartz OSL and tephra ages up to 600 ka provide age control. After a preheat of 320°C (60 s), the polymineral fine grains (4–11 μm) were bleached with IR at 50°C (200 s) and the IRSL was subsequently measured at 290°C for 200 s. In general, the fading uncorrected post-IR IRSL ages agree with both the quartz OSL and the tephra ages. We conclude that the post-IR IRSL signal from these samples does not fade significantly and allows precise and accurate age determinations on these sediments.

Mechanisms Underlying Pulsed Infrared Stimulation of Cardiomyocytes

In this study, we investigated the origins of the endogenous cellular mechanisms underlying IR (1862 nm, 3-4 ms/pulse, 9.1 - 11.6 J/cm2 /pulse, Capella, LHM Aculight) stimulation of neonatal rat ventricular and adult rabbit ventricular cardiomyocytes, in vitro. Confocal imaging (FV1000, Olympus; Fluo-4 AM, 4-6 μM, Invitrogen) of neonatal cardiomyocytes revealed IR-induced transient [Ca2+]i responses consisting of a rapid [Ca2+]i buffering component, discernable during periods of elevated [Ca2+]i, followed by consistent, sub-threshold [Ca2+]i rises that resulted in visible cell contractions with each IR pulse. Pharmacological block of the IR-evoked responses in neonatal cardiomyocytes with CGP-37157 (20 μM, N=12 cells) and Ruthenium Red (40 μM, N=13) suggested an integral role of the mitochondrial Ca2+ transporters in the IR-induced [Ca2+]i cycling in neonatal cardiomyocytes. While initial results with adult cardiomyocytes during comparable IR stimulation also revealed visible contractile responses, the corresponding [Ca2+]i transients were surprisingly not detected. To further investigate the response in adult cardiomyocytes, whole cell patch clamp measurements were performed to monitor sarcolemma membrane potential (Vm) changes during IR stimulation. Preliminary data revealed either depolarizing or hyperpolarizing Vm responses in the cells, the nature of which was determined by the relative timing of the IR pulse applications to threshold, electrically-induced cell depolarization. Based on these findings, additional efforts focused on resolving the extent and nature of this sarcolemmal involvement in the IR-evoked responses of both neonatal and adult cardiomyocytes.

Stability of IRSL signals from sedimentary K-feldspar samples

Recent work has identified IR stimulated luminescence signals at elevated temperature from both potassium- and sodium-rich feldspars that have much lower anomalous fading rates than the conventional signal measured using IR stimulation at 50°C. This paper examines the stability of these signals for potassium-rich sedimentary feldspars. We show that the natural post-IR IRSL (pIRIR) signal from a 3.6 Ma old sample is in apparent saturation on a laboratory generated dose response curve, i.e. it does not show detectable fading in nature although a low fading rate is observed on laboratory time scales. We show that the pIRIR signal has a greater thermal stability than the IRSL signal and that the trend in increasing thermal stability is mirrored by a decreasing fading rate. We also investigate the effect of preheat temperature and IR stimulation power on the decay shape and conclude that the data can be explained in terms of either a single- or multiple-trap model. We present evidence that may suggest that at least part of pIRIR signal is derived from a high temperature trap (∼550°C thermoluminescence (TL) peak), although again the data can also be explained in terms of a single-trap model. Finally, we present dose response curves and characteristic curvature constants (D0) values for various IRSL signals and conclude that the more stable signals saturate more quickly than the less stable signals and that the initial and final signals saturate at approximately the same level.

Thermal stability of infrared stimulated luminescence of sedimentary K-feldspar

Abstract The thermal stability of the infrared stimulated luminescence (IRSL) signal measured at 50 °C as a function of IR stimulation time was investigated using KF grains extracted from sediments from central China. A dependence of thermal stability of IRSL signal on IR stimulation time and stimulation temperature were observed in pulse annealing studies. Relatively lower thermal stability is given by the initial part of the IRSL measured at 50 °C, than the later part of IRSL curve. Based on these observations, the thermal stability of the post-IR IRSL signal stimulated at elevated temperatures (100–200 °C) was also investigated. It was found that at least two groups of traps (shallow and deep) are associated with the IRSL and post-IR IRSL signals. The IRSL signal obtained at 50 °C is mainly from the shallow traps while the post-IR IRSL obtained at elevated temperatures is mainly from the deep traps. The kinetics parameters obtained using pulse annealing test indicate that the shallow IRSL traps are probably associated with the ∼300–350 °C TL peak and the deep traps are probably associated with the ∼400 °C TL peak. The shallow traps (∼350 °C TL peak) are associated with those easy-to-fade traps and the deep traps (∼400 °C TL peak) are associated with hard-to-fade traps.

Optically stimulated phosphorescence in orthoclase feldspar over the millisecond to second time scale

Abstract In the past, time-resolved IR stimulated luminescence (TR-IRSL) curves from feldspar have mainly been measured over a few hundred μs with the purpose of estimating the lifetimes of the components. In this study, we present the decay form of time-resolved IRSL and IR stimulated phosphorescence (IRSP) from orthoclase feldspar covering over 8 orders of magnitude (50 ns to ∼7 s). A detailed characterisation of the slowly decaying signals (ms to s time scales) from feldspar is undertaken to obtain further insight into the role of re-trapping in both the IR stimulated luminescence (IRSL) and the relatively more stable post-IR IRSL signals. The decay form of the different signals examined here shows a weak dependence on preheat temperature and a strong dependence on stimulation temperature. Interestingly, the IRSP curves show a conspicuous kink of which the position is linearly dependent on the on-time duration. The data on thermal dependence of these signals might suggest that the decay behaviour of the time-resolved IRSL and phosphorescence signals mainly reflect the occupancy of electrons in the band tail states with a significant contribution from the shallow traps. This interpretation is supported by thermoluminescence (TL) curves showing the photo-transfer effect during short IR and post-IR IR stimulations.

The effect of preheating on the IRSL signal from feldspar

It is difficult to relate the IRSL signal from feldspar to a particular region of the TL curve; prior IR stimulation reduces the TL signal over a wide range of temperatures. Such data are apparently consistent with the observation from pulse anneal experiments that a laboratory-induced IRSL signal is detectably eroded by a relatively low temperature preheat. These results can be explained by a distribution of trap depths of IR sensitive traps, and/or by changes in recombination probability induced by IR exposure. To investigate the relative importance of these processes, we first examine the relationship between the loss of blue IRSL and TL signals with preheating, and the effect of prior IRSL on the TL signal. Using IRSL measured at 50 °C and a SAR protocol, we then examine the dependence on preheat temperature of equivalent dose (D e), laboratory fading rate ( g), and the resulting luminescence age, from three sedimentary potassium-rich feldspar extracts. We demonstrate that there is no systematic increase in D e for a preheat temperature range from ∼80 °C to ∼320 °C (60 s duration). After fading correction, age plateaus vary slightly over the temperature range examined, but there is no evidence for an increase in age with preheat temperature. We therefore conclude that the main dosimetry trap(s) in feldspar are not significantly eroded by laboratory heating for up to 60 s at 320 °C, and we tentatively identify the source of this IRSL as a TL peak lying between 410 and 420 °C; this suggestion is consistent with a kinetic analysis of sensitivity-corrected IRSL data. The corollary to our observations is that shallow (unstable) traps do not give rise to a significant IRSL signal.

Assessment of diagnostic tests for evaluating the reliability of SAR D e values from polymineral and quartz fine grains

In this study, we applied optically stimulated luminescence (OSL) dating to two fine grain sediment samples collected at Jeongokri, Korea. A single aliquot regenerative dose (SAR) procedure was applied to both polymineral grains and to chemically isolated (H 2SiF 6) quartz grains of 4–11 μm diameter. For polymineral fine grains, the OSL IR depletion ratio and the equivalent dose (D e) plateau test appear to be equally sensitive indicators of appropriate IR stimulation time for use in the ‘double SAR’ protocol. Additionally, the OSL IR depletion ratio test gives an indication of the relative mineral composition of the samples, hence providing an assessment of the likelihood of obtaining a quartz-dominated [post-IR] OSL signal. Use of higher preheat temperatures would assist in thermally eroding the non-quartz component of the [post-IR] OSL signal from polyminerals. For the quartz fine grains, data from both natural D e determinations and laboratory dose recovery tests are required to identify the appropriate preheat temperatures for dating, due to problems of thermal transfer. This phenomenon is particularly exaggerated for these samples due to the large D e values (≥350 Gy) and hence low slope of the dose–response curve. The double SAR method cannot be applied ubiquitously, even after careful and rigorous study of one sample from a section. Quartz OSL dating using a range of preheat temperatures is suggested to be the most suitable method for OSL dating of fine grain sediments.

Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts

Feldspar as a retrospective dosimeter is receiving more and more attention because of its useful luminescence properties; in particular the dose response curve extends to significantly higher doses than quartz. However, feldspars have one major disadvantage; both the thermoluminescence (TL) and optically stimulated luminescence (OSL) signals exhibit anomalous (athermal) fading. Much of the OSL work carried out on feldspars in recent years has focussed on determining fading rates and correcting for them. Almost all work has been carried out using IR stimulation at 50 °C detected in the blue region of the spectrum. In contrast, we have determined fading rates for various sedimentary feldspar samples using different stimulation and detection windows. If the initial part of the OSL signal is used the lowest fading rate is observed with post-IR blue stimulation (UV detection), but if a later part of the signal is used the lowest fading rate is obtained for IR stimulation (blue detection). Daylight bleaching experiments show that, unlike quartz, the initial and final parts of the feldspar OSL signal bleach at approximately the same rate. Stimulation at elevated temperatures significantly reduces the apparent fading rate. This signal appears to bleach more rapidly in daylight than the signal observed when stimulation is at 50 °C (for IR stimulation and blue detection). We conclude that there are OSL signals from sedimentary feldspars which fade at a significantly lower rate than the signal used conventionally, and that further testing of these signals is warranted to see if they are dosimetrically useful.

Recombination processes in the Y3Al5O12:Ce3+ scintillator

The roentgenoluminescence spectra, temperature-dependent activator luminescence, optically stimulated luminescence, and the effect of IR irradiation on the yield and spectral composition of the low-temperature roentgenoluminescence and thermoluminescence curves of the Y3Al5O12:Ce3+ scintillator have been studied in the temperature range 85–295 K. The results, coupled with earlier data, suggest that the Ce3+ ions in the garnet crystal studied form Ce3+p hole centers and increase the concentration of electronic F−-centers responsible for the IR stimulation band at 940 nm. The reduction in roentgenoluminescence yield on cooling Y3Al5O12:Ce3+ to below 230 K is due to the significant localization of excited carriers at defects, which show up in thermoluminescence peaks and optical stimulation spectra. The low-temperature Ce3+ luminescence in Y3Al5O12:Ce3+ seems to result from the recombination of activator-bound excitons.

Effects of Feldspar Contamination on Equivalent dose and the Shape of Growth Curve for OSL of Silt-Sized Quartz Extracted from Chinese Loess

This study examines the effects of feldspar contamination of different extent (by fluorosilicic acid etching for different time periods and mixing pure quartz with different percentage of unetched grains) on blue-light stimulated luminescence (BLSL) of quartz (38-63 μm) for Chinese loess. In particular, the De values and the shape of growth curves will be examined. The results show that: (1) The De determined using feldspar in Chinese loess is obviously underestimated, and infra-red stimulated luminescence (IRSL) has a greater underestimation than BLSL. For aliquots with no fluorosilicic acid etching, an IRSL De underestimation of ∼30% is observed for a sample with an expected age of ∼22 ka, ∼19% underestimation for BLSL, and ∼10% for post-IR BLSL. For quartz BLSL, the contamination of feldspar, which has not dissolved by fluorosilicic acid etching, will inevitably lead to age underestimation. We suggest that the IR-checking should be performed for every single aliquot. An aliquot should be excluded from the final De calculation if obvious IRSL signal was observed. (2) For the sample under examination blue LED stimulation can reset both IRSL and BLSL signals of feldspars, while IR stimulation cannot reset the BLSL of feldspars. (3) For multiple-mineral aliquot the growth curve shape of the post-IR BLSL is different from that of the IRSL, and within 25 Gy it is identical to that of the pure quartz BLSL. The contamination of feldspars in quartz will change the shape of a growth curve for quartz BLSL.