OSL Components Research Articles

Investigating the OSL components and the sensitivity changes in a natural quartz crystal showing an intense post-sensitization TL signal

This study aims to investigate the optically stimulated luminescence of quartz grains exhibiting an intense thermoluminescent signal between 250 and 350°C after sensitization with a high dose of gamma radiation and moderate heat treatments. Pellet discs produced with zeroed and sensitized grains were irradiated with test doses ranging from 0.5 to 40 Gy. After sensitization, the OSL signal of the fast component stimulated with blue light increased more than 1000 times. Annealing at 400°C was adopted to erase the residual signal. The sensitivity changes were assessed after various TL and OSL readings. The annealing cycles were responsible for a significant increase in OSL and a 20% reduction in TL signals. The analysis of the residual TL indicated that the traps responsible for the main components of the sensitized peak (280°C) are harder to bleach than those related to the so-called 110, 325, and 375°C peaks. The sensitivity changes and the relationship between OSL and TL signals were explained in terms of a mechanism of competition involving active and deep electron traps. No correlation was observed between the fast OSL component and the 325°C TL peak.

Determining the kinetic parameters of traps in quartz using the thermally modulated OSL method

The parameters of traps in quartz determine the thermal stability of OSL components and define the time range of dating. Their precise values are crucial for the thermal history of rock modelled in OSL thermochronometry. The values of trap parameters appearing in the literature depend on the quartz sample tested and the method used, even in the case of the most widely researched fast OSL component. Recently, it was found that it is possible to effectively separate the fast OSL component in quartz when the thermally modulated OSL (TM-OSL) method is conducted using a wavelength of 620 nm. Here, the possibility of fast component separation by the TM-OSL method for measuring OSL thermal depletion curves (OTDC) (isothermal OSL decay) and so-called TL difference curves (the TL signal bleached during the optical stimulation) is used. Trap parameters obtained independently in the OTDC experiments and by the IR and VHR methods applied to TL difference curves are compared. The parameter values stay in agreement in all methods used for three quartz samples from sediments of various origins. The new approach to measuring the OTDCs with the TM-OSL method enables the best precision. The mean value of trap parameters obtained in all methods and for all samples (E = 1.66 ± 0.02 eV, s = (4.1 ± 2.4) × 1013 s−1) is consistent with the literature data. TL difference curves are fitted with satisfactory quality by a first-order kinetics peak using the obtained trap parameters.

Luminescence dating of heated quartz extracted from burnt clay and pottery excavated from the Lingjiatan archaeological site, China

This study utilizes OSL-SAR, TL-SAR, and TL-MAAD methods to date heated quartz extracted from burnt clay and pottery samples from the Lingjiatan archaeological site, China. The OSL components of the heated quartz were determined by deconvoluting the CW-OSL curve, and the Fast Ratio value was used to distinguish whether the initial OSL signal was dominated by the fast component. The results show two types of quartz OSL characteristics in the initial signals: Type I is dominated by the fast component (Fast Ratio values > 10), while Type II is dominated by the medium and slow components (Fast Ratio values < 10). Type I samples show bright OSL signals, and a preheat plateau appears from a relatively low temperature. The recuperation is negligible, and reliable equivalent doses can be obtained using the conventional OSL-SAR measurement conditions. In contrast, the OSL signal of Type II samples is relatively dim, and the preheat plateau appears from a much higher temperature than in Type I samples. The recuperation of Type II samples increases significantly at higher preheat temperatures. Significant De underestimation of Type II samples was observed at lower preheat temperatures. It is noted that the thermal transfer effect can be attenuated by increasing the OSL stimulation temperature. Therefore, a modified OSL-SAR measurement condition, with higher preheat, cut-heat and stimulation temperatures, was used to date Type II samples. The OSL-SAR ages of most of these two types of samples agree well with the independent 14C ages, demonstrating that OSL-SAR can be used to date heated archaeological materials at high firing temperatures (∼900°C). The Lingjiatan archaeological site was determined to be approximately 5.4–5.8 ka BP 2022.

New correlation between PTTL and POSL components in Al2O3:C

We describe newly found correlations between thermoluminescence (TL), pulsed optically stimulated luminescence (POSL), and phototransfer TL (PTTL) signals in Al2O3:C. A set of Al2O3:C samples were characterized for their TL and OSL curve shapes, as well as TL/POSL integrals and correlated with their PTTL behavior. POSL was used to separate the contribution from fast UV emission (F+ centers) and slow blue emission (F centers) OSL components in Al2O3:C. The results show that samples with high PTTL exhibit TL curve shapes with a peak at higher temperatures and OSL curves that decay slower compared to samples with low PTTL. The ratio of the integral POSL components, the UV/B ratio, was found to inversely correlate with the PTTL. We discuss the possible causes of our observations and outline the limitations of commonly used luminescence models to explain our data. These correlations add yet another piece to the puzzle of the stimulated luminescence mechanisms of Al2O3:C.

Component-Resolved Analysis Towards Correlation between Thermoluminescence and Optically Stimulated Luminescence in Commercial Magnesium Oxide

Abstract The present study aimed at quantifying the relationship between TL and either CW-OSL or LM-OSL using commercially available magnesium oxide. The samples were bleached at two different temperatures, and a component-resolved analysis on the integrated signals was performed. According to the data of the present study, each one among the five observed LM-OSL component receives electrons from at least two different TL peaks. Two different fast OSL components were resolved in the LM-OSL curves, both accumulating electrons from all TL glow peaks with Tmax>150°C. Component C3 is very well correlated with the TL peaks at 102, 135 and 194°C, while components C4 and C5 are related to the TL glow peaks of 292°C, 353°C and 464°C. We note that for CW-OSL the resolution is good when two or more components differ in intensity by an order of magnitude. Blue stimulation depletes substantially the first two TL peaks but not the third peak. Substantial depletion of the high-temperature TL peaks is achieved only by using the LM-OSL configuration. The results of the present study suggest that the traps that contribute to TL and OSL are the same, despite using different recombination pathways.

CW-OSL, LM-OSL and TL Dating of Bricks from Karakorum, Mongolia: Insights from TL Spectra

In this study, we present results of luminescence dating using CW-OSL, LM-OSL and TL on heated quartz from the archaeological and historical site in Karakorum – the ancient capital of Mongolia, to test their convergence with the age control in the form of the Karakorum inscription 1346. The TL spectra conducted on quartz from red and grey coloured bricks appeared to be characteristic of the technological origin. Quartz TL from red bricks showed a UV emission band at ∼360 nm and a strong fast OSL component dominated signal. In contrast, blue emission detected in the TL spectra of grey coloured bricks, resulting possibly in the medium component dominated OSL signal. Finally, OSL and TL results gave dates from 1180±70 AD to 1360±70 consistent with the expected ages.

Bleaching of blue light stimulated luminescence of quartz by moonlight

Moonlight is sunlight reflected from the moon’s surface. It is additionally modulated by the Earth’s atmosphere, dust and pollutants on its way to the surface of the Earth. This contribution reports the bleaching rates of blue light stimulated luminescence (BLSL) signal of Quartz under full moonlight exposure at the Earth’s surface. Quartz BLSL reduced to 70% by an exposure of 5 hrs moonlight, is in contrast to ~90% reduction in < 3 s with daylight. This was anticipated due to (a) reduced moonlight flux by about a factor of half a million (Agrawal in Lat. Am. J. Phys. Educ. 4(2):325–328, 2010; J. Phys. Astron. 5(1):1–15, 2017); (b) inverse power law dependence of bleaching efficiency on wavelength (Spooner in The validity of optical dating based on feldspar, Ph.D. Thesis, Oxford University, Oxford, 1993; Chen and McKeever in Theory of Thermoluminescence and related phenomena, World Scientific Publications, London, 1997, Chen and Pagonis in Thermally and optically stimulated luminescence: A simulation approach, Wiley and Sons, Chichester, 2011); and (c) moonlight and daylight have spectral peaks around 650 and 550 nm, respectively. Deconvolution of OSL components suggests that moonlight affects the fast component of OSL signal the most. This has ramification for the application in polar regions, where the availability of daylight is at a premium during the winter months. Within a given context, it is conjectured that this could be used to infer the seasonality of sediment transport.

Slow OSL component in quartz separated by TM-OSL method

The thermal stability of the slow component measured by the thermally modulated optically stimulated luminescence (TM-OSL) method was investigated for quartz from geological sediments. The TM-OSL stimulation was carried out with the stimulation wavelength of 470 nm and the heating rate of 2 Ks−1 after the effective bleaching of the faster components. This TM-OSL component is known to saturate for a relatively high doses with comparison to the OSL signal commonly used for dating and because of that gives hope for extending the time range of luminescence dating. Both in the thermal depletion curves of TM-OSL signal as well as in the dependency of the TM-OSL intensity on the preheat temperature the complex nature of this signal is revealed. The analysis of the depletion curves does not allow to obtain a reliable values for the parameters of traps responsible for the investigated TM-OSL process.

Gamma dose rate effects in luminescence signals of various artificial, well established dosimetric phosphors

The present work attempts to study tentative gamma dose rate effects for the stable TL and OSL signals of specific, well established artficial luminescence dosimeters. Two different dose rates of gamma radiation (2 and 31 Gy/h) were used. The study has been performed to the stable TL peaks of 5 different TL phosphors (LiB4O7:Cu,In; MgB4O7:Dy,Na; LiF:Mg,Ti; CaF2:Dy; BeO) as well as to both OSL components of BeO. Tentative dose rate effects were studied for both dosimetric dose response features as well as kinetic parameters after deconvolution for both signals. Two different groups of materials were revealed. The first one includes materials such as LiF: Mg,Ti, BeO and MgB4O7: Dy,Na; for these, both TL dose response features and TL kinetic parameters are independent on the dose rate. This is also the case for both OSL components of BeO besides the linearity index of the dose response of the fast OSL component; the latter seems to mildly depend on the dose rate. At the same time, experimental arguments based on both dosimetric as well as deconvolution features suggest the presence of tentative dose rate effects for the cases of LiB4O7:Cu, In and CaF2:Dy. Moreover, the effective use of these aforementioned features as probes for identification of dose rate effects is also discussed. The results of the present study suggest that the basic postulate of most phenomenological TL models that traps pre-exist and they are simply filled during irradiation has to be reconsidered.

A correlation study on the TL, OSL and ESR signals in commercial BeO dosimeters yielding intense transfer effects

BeO ceramics have been used for quite a long time as radiation dosimeters besides being used in many other areas. BeO dosimeters can be stimulated both thermally and optically, giving rise to TL and OSL signals. BeO has two main dosimetric peaks, 2 and 3, by ignoring peak 1 that corresponds to a shallow trap, while the OSL curve is composed of two components, termed as C1 and C2. Irradiated BeO dosimeters showed ESR spectra at room temperature consisting of three centers I, II and III. These centers were assigned to Al+2 and O- centres; two different typical oxygen centre behaviours were monitored, one showing anisotropic and one isotropic properties. The present study attempted to perform correlation between the TL peaks 2 and 3, the CW-OSL components C1 and C2 and ESR centers I, II and III. The bleaching and decay features of the ESR centers are presented for the first time in the literature. The OSL component C1 is correlated with the TL peak 2; both luminescence entities are associated with the ESR center I, attributed to the Al+2 center. Finally, thermal stability of center II suggests that it can be also tentatively correlated to both TL peak 2 and OSL component C1. Moreover, the present study provides strong experimental arguments towards a correlation between TL peak 3, CW-OSL component C2 and ESR center III, namely oxygen ion (isotropic). Intense transfer was monitored either (a) from deeper traps to both traps responsible for TL peaks 2 and 3, as well as (b) from the trap of TL peak 3 to that of TL peak 2. Nevertheless, reconstruction as well as indirect TA-OSL signal monitoring indicates that the transfer is more intense to the trap corresponding to TL trap 3. For this reason, even after depleting both TL peaks, intense OSL curves were still measured.

Different components of the quartz OSL signal resolved by the TM-OSL method

Recently it has been shown that the thermally modulated optically stimulated luminescence (TMOSL) method, which is based on optical stimulation during linear heating of the sample, can be used successfully to extract the individual OSL components during the experimental stage. Such a possibility is important in OSL dating of sediments, where using the OSL component that is most easily bleached in nature is the prerequisite for correct results. The TM-OSL measurements help also to correlate the optical depth of a trap with its thermal depth which enables to determine the thermal stability of traps active in the OSL process. This is especially significant in thermochronometry where the prediction of the temperature and time dependence of the stimulation processes in mineral grains is the main problem. It has been showed that the fast component of OSL in quartz can be separated from the others by optical stimulation with the wavelength of 620 nm. Here, it is shown how the slower OSL components in quartz can be measured individually using the TM-OSL method with the wavelengths of stimulation light in the range 450–620 nm. The growth curves for these components and results of the first tests of their thermal stability are presented.

Assessing the reproducibility of quartz OSL lifetime determinations derived using isothermal decay

Signal stability is a key consideration when using luminescence dating techniques. The stability, or lifetime, of a signal is one of the factors determining the upper age constraint for luminescence dating, and it has been suggested that the signal being used for dating should have a lifetime at least ten times the age being dated in order to limit age underestimation to an upper loss of 5%. Accurate derivations of signal stability and associated kinetic parameters, such as trap depth and frequency factor, are also important parameters for constraining rock cooling histories in thermochronometric techniques. This paper aims to assess the reproducibility of lifetime determinations derived using isothermal decay measurements. Variability arising from changing the isothermal decay protocol used is tested. Simulating Arrhenius plot from fixed trap depth and frequency values shows that whilst trap depth can be relatively well constrained, significant variability in the frequency factor, hence signal lifetime, should be expected. This paper also uses luminescence signals measured using different wavelengths to better understand the impact of signal from non-fast quartz OSL components in lifetime calculations. The presence of contributions from non-fast OSL components in the initial part of the OSL signal can result in the lifetime being calculated from charge contributions from multiple traps, not solely the 325 °C TL peak, as has been previously assumed. This effect can be reduced however by stimulating luminescence signals with longer wavelengths to better isolate signal from the fast component.

Thermally modulated optically stimulated luminescence (TM-OSL) of quartz

It has recently been shown in computer simulations of the OSL process that increasing the temperature during optical stimulation allows the probability of electron excitation from traps to the conduction band to be modulated. This, in turn, facilitates the efficient separation of individual OSL components. A result of the thermally modulated OSL (TM-OSL) measurement method is a peak shaped curve. In addition, the position of the TM-OSL peak on the temperature axis can be controlled by the stimulation energy, heating rate and photon flux used for optical stimulation. Here, the results of a TM-OSL study for natural quartz samples are presented. The basic features of the TM-OSL curves of quartz are shown for different parameters that control their shape. The investigation is focused on traps that are most sensitive to light and which are the source of the OSL signal that is the most useful in retrospective dosimetry. A method by which it can be measured separately from the slower components is presented. The very first attempt at directly estimating the optical depth and the parameters determining the strength of the electron-phonon coupling for the traps responsible for the fast OSL component in quartz has been made.

P.2.d.022 - Inflammatory cytokines influence cortical thickness in bipolar disorder

It has recently been shown in computer simulations of the OSL process that increasing the temperature during optical stimulation allows the probability of electron excitation from traps to the conduction band to be modulated. This, in turn, facilitates the efficient separation of individual OSL components. A result of the thermally modulated OSL (TM-OSL) measurement method is a peak shaped curve. In addition, the position of the TM-OSL peak on the temperature axis can be controlled by the stimulation energy, heating rate and photon flux used for optical stimulation. Here, the results of a TM-OSL study for natural quartz samples are presented. The basic features of the TM-OSL curves of quartz are shown for different parameters that control their shape. The investigation is focused on traps that are most sensitive to light and which are the source of the OSL signal that is the most useful in retrospective dosimetry. A method by which it can be measured separately from the slower components is presented. The very first attempt at directly estimating the optical depth and the parameters determining the strength of the electron-phonon coupling for the traps responsible for the fast OSL component in quartz has been made.

TL and OSL studies of carbon doped magnesium aluminate (MgAl2O4:C)

The MgAl2O4:C has been synthesized by using two different methods by electron gun and vacuum assisted melting of MgAl2O4 in presence of graphite. The MgAl2O4:C phosphor thus developed by these two different methods have similar types of the TL/OSL defects with multiple overlapping TL glow peaks from 100°C to 400°C. The Computerized Curve De-convolution Analysis (CCDA) has been used to measure TL parameters such as thermal trap depth, frequency factor and order of kinetic associated with charge transfer process in TL phenomenon. The investigated TL/OSL results show that these two methods of incorporating carbon in MgAl2O4 have generated closely resemble the defects of similar types in MgAl2O4:C lattice. However, the MgAl2O4:C synthesized by electron gun shows relatively larger concentration of the TL/OSL defects as compared to MgAl2O4:C synthesized using vacuum assisted melting method. The photo-ionization cross-section (PIC) associated with fastest OSL component of MgAl2O4: C is found to be ∼ 0.5 times than that of fastest OSL component of commercially available dosimetric grade α-Al2O3:C. The MgAl2O4:C thus developed shows good dynamic OSL dose linearity from few mGy to 1Gy. This work reveals that MgAl2O4:C could be developed as potential tissue equivalent OSL / TL material.

Mathematical formulation of Tmax–Tstop method for LM-OSL and its experimental validation on α-Al2O3:C

A mathematical formulation and its experimental validation on α-Al2O3:C for evaluating the number of OSL components has been described. The method consists of various partial bleaching steps of LM-OSL curve and as a result, the peak position (Tmax) of the resultant curve shifts if the system contains multiple components. However, for single component system the peak position of the resultant curve doesn’t change on partial bleaching for a phosphor obeying first order kinetics. The method has been theoretically formulated for single and multiple component system with different order of kinetics and validated experimentally on the commercial α-Al2O3:C OSL phosphor. The slope of the curve between shift in Tmax and bleaching time gives the number of the OSL components and measure of their closeness in terms of photoionization cross-section. Based on this result, the photoionization cross-section of the two embedded peaks in the LM-OSL curve of α-Al2O3:C were found to be 1.51×10−18cm2 and 5.02×10−19cm2 using CW-OSL and NL-OSL method.

Quartz fast component opticallystimulated luminescence: Towards routine extraction for dating applications

Using an uncontaminated fast component is a key for improving the reliability of quartz OSL dating for many deposits. So far no approach to extract the fast component of quartz OSL has routinely been adopted for dating practice. Key challenges for extracting fast components are (1) the difficulty of finding a unique solution in curve-fitting deconvolution of OSL decay curves and (2) the relatively poor dating precision when using experimental fast component extraction. Here, a simple mathematic solution for fast component extraction is presented that is not relying on curve-fitting deconvolution and can easily be adopted into routine dating practices. By using specifically selected data points from smoothed OSL decay curves, the precision of equivalent doses calculated using the extracted fast component can be improved over equivalent doses calculated using bulk OSL. The fast component extraction is tested on a group of age-constrained samples containing both insufficiently bleached and sufficiently bleached deposits. Fast component OSL ages are as accurate as bulk OSL ages for the sufficiently bleached deposits, but more accurate for samples where bulk OSL is affected by insufficient bleaching. We also demonstrate how using a curve smoothing procedure can improve dating precision in case of both sufficiently and insufficiently bleached deposits.

A new irradiated quartz for beta source calibration

For luminescence dating to be an accurate absolute dating technique it is very important that we are able to deliver absolutely known radiation doses in the laboratory. This is normally done using a radiation source (alpha, beta, X-ray) calibrated against an absolutely known reference source. Many laboratories have used the various different batches of Risø calibration quartz for the calibration of beta and X-ray sources, but these have been largely undescribed. Here we describe in detail the preparation and luminescence characteristics of a new quartz standard, based on a North Sea beach sand collected from south-western Denmark (Rømø). Two grain sizes (4–11μm and 180–250μm) have been examined in detail. These were pre-treated (annealed, dosed and annealed again) to sensitise and stabilise the luminescence signals before being given an absolutely known gamma dose from a point 137Cs source in scatter-free geometry. The luminescence characteristics are described; the very intense blue-light stimulated signal is dominated by the fast OSL component and the IR-stimulated signal is negligible. The material is shown to be suitable for measurement using SAR, and the dose recovery ratio is indistinguishable from unity with a standard deviation of <2% for multi-grain aliquots. The material is also shown to be suitable for single-grain calibration, with >80% of the grains giving a useful signal. Although there is an unexplained dispersion in our calibration data of ∼3% (which we cannot attribute to instrument variability), we nevertheless conclude that this material is very suitable for transferring absolute known doses from a standardised gamma source to in-built irradiation sources.

Equivalent dose of quartz originating from ceramics obtained by OSL SAR method – Tests of protocol parameters

In the standard OSL dating procedure, the OSL signal is measured at 125 °C. For quartz samples from bricks the presence of traps responsible for the 160 °C and 200 °C TL peaks has an influence on the OSL process, just like the one for the traps responsible for the 110 °C TL peak. In order to examine the significance of this disturbance for dating results, a series of measurements of De was carried out for various temperatures of the OSL readout in SAR protocol. For most samples, significant fluctuations of De values were obtained, especially at temperatures above 90 °C. Also the analysis of OSL components carried out for curves obtained at different measurement temperatures shows that the TL traps active up to 200 °C make the OSL process more complex. The measurement at 125 °C does not assure the exclusion of shallow traps from the OSL process. A reasonable solution of this problem may be the choice of temperatures below the range of dominant TL peaks, in the SAR protocol for OSL measurements.

Insights into TT-OSL signal stability from single-grain analyses of known-age deposits at Atapuerca, Spain

Single-grain thermally transferred optically stimulated luminescence (TT-OSL) dating has recently been applied to a number of the Atapuerca palaeoanthropological sites. As yet, however, there have not been any direct assessments of TT-OSL signal stabilities for specific grains used for dating. In this study, we undertake a series of TT-OSL suitability assessments on known-age samples from Gran Dolina and Sima del Elefante. Our results suggest that the Atapuerca samples contain populations or sub-populations of grains with suitably stable TT-OSL signals for dating over late-Early and Middle Pleistocene timescales. Equivalent dose (De) distribution analysis in combination with pulse-annealing assessments provides a useful means of identifying inter-grain and inter-sample differences in TT-OSL signal stabilities. We also show that obtaining De values using different preheat conditions may help to identify potentially problematic TT-OSL behaviours. Analyses of multi-grain aliquot TL curves for these samples reveal that 'bulk' TL signal loss experiments may provide limited insights into TT-OSL source trap lifetimes due to averaging effects, the dominance of grain populations that do not produce TT-OSL, and interference from slowly bleaching OSL components. Our results improve the robustness and precision of existing TT-OSL chronologies for units TD6-3 and TE16-TE17 at Gran Dolina and Sima del Elefante, and support the broader suitability of the single-grain TT-OSL approach at the Atapuerca sites.