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To understand a luminescence dating report, it’s important to understand how luminescence data is collected and how ages are calculated. A luminescence age is calculated using the equation:
Age (ka) = De (Gy) / Dr (Gy/ka)
where De refers to the equivalent dose of a sample and Dr refers to the dose rate of the sample and its burial environment. The laboratory workflow (Fig. 1) is centered around measuring these two variables.
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Figure 1. General laboratory workflow for determining a luminescence age. “De” refers to the equivalent dose and “Dr” refers to the dose rate. ICP-MS/AES—inductively coupled plasma–mass spectrometry/atomic emission spectrometry; NAA—neutron activation analysis. From Mahan et al. (2022).
Field sampling
Of course the first step in dating a site involves collecting the sample in the field (Fig. 1). Samples for luminescence dating can be collected in many ways, and can include different types of material. Materials most commonly dated are grains of sand or silt, however rock surfaces, pottery, rock art, and even archaeological constructions such as walls and buildings have been sampled.
Because luminescence dating methods determine the last time a mineral has been exposed to light or heat, it is imperative that the sample is not contaminated by modern light or heat during the sampling process. Appropriate collection procedures depend on the type of sample being collected and details of the site itself. Detailed instructions should be provided by a luminescence dating expert for complex sites.
Common methods for sample collection include:
hammering an opaque tube (e.g., steel) into a sedimentary section
collecting sediments, lithic artefacts, or rocks in a light-safe environment (e.g., under a light-proof tent or at night)
hand augering
carving a cohesive block of sediment from a sedimentary section
extracting samples from sediment cores in a light-safe environment
drilling cores from rock surfaces in a light-safe environment
collecting buried artefacts quickly (>30 s) in a shadowed environment
sample extraction from buildings (chiselling, coring, etc.)
Where possible, it’s also advisable to collect “modern samples”. Modern samples allow us to check how well the luminescence signal is re-set during sun-exposure in a particular depositional environment. This allows us to evaluate ages from our ancient samples, by determining the likelihood that their signals were also fully re-set prior to burial. The modern sample should be collected from rocks or sediments that have experienced the same mode of transport and deposition as the ancient samples. Unfortunately, even when this is the case, there is always the possibility that the bleaching history of the modern sample will not be representative of the ancient samples collected at the same site (e.g., Langston et al., 2025).
Dose rate sample preparation
In addition to samples collected for measurement of the luminescence signal and De, samples must be collected and prepared for the measurement of the dose rate (Fig. 1). How dose rate samples are prepared depends on how they will be measured. For samples measured using ICP-MS, for instance, samples will be split using a riffle sample splitter, dried and ground to a flour consistency before measurement. For lab-based gamma spectrometry, samples must be split, dried, then ashed at 450-500℃ for 24 hours, milled to a fine sand consistency prior to mounting in a Radon-leak proof container or mould. These samples will then be stored for 21 days to allow radionuclides in the U-series decay chain to reach equilibrium prior to measurement.
The dose rate sample will be weighed before and after drying to obtain an estimate of the sample water content. This is important for estimating the average water content of the sample during its burial history as water attenuates radiation and can significantly affect the dose rate to the sample.
Equivalent dose sample preparation
Samples collected for luminescence measurement are prepared in order to isolate target minerals that have luminescence signals suitable for dating (Fig. 1). This preparation typically includes sieving, acid digestion to remove carbonates, and hydrogen peroxide treatment to remove organic material. Minerals can be further isolated by heavy liquid density separation and/or hydrofluoric acid treatments.
Both quartz and feldspar are commonly used for luminescence dating, however, the choice of which mineral is dated depends on its abundance in the sample, as well as its luminescence characteristics. Feldspar exists as a range of mineral species, but the one most commonly used in luminescence studies is potassium (K-) feldspar. All types of feldspar typically suffer from a phenomenon called “anomalous fading”, where the luminescence signal decreases from otherwise stable traps through geological time. There are two approaches to overcome anomalous fading. First, the fading rate of each sample can be measured and corrections can be made if the fading rate is not too high. Second, specific measurement protocols (such as a post-IR IRSL protocol) can be used to target non-fading, or less-fading, signals from various feldspars.
Most sediment samples collected in Australia can be dated using quartz. This is because naturally occurring Australian quartz often has a very bright luminescence signal that is well-suited for dating; it is bright, easily bleachable, and does not fade.
For rocks or artefacts, samples are typically cut or cored in the lab using water-cooled precision drilling and cutting equipment. Subsamples are then sliced into thin sub-millimeter-thick slices for luminescence measurement. If the rock or artefact is fissile and breaks apart during cutting, slices can be gently ground using a mortar and pestle and measured as multi-grain aliquots.
Equivalent dose (De) measurement and analysis
The equivalent dose (De) of a sample is an estimate of the radiation dose that the sample received in the burial environment. When we measure the luminescence signal from a sample, the brightness of this sample is proportional to the De value and therefore its burial age (Fig. 2).
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Figure 2. Illustration showing the depletion of a sample’s luminescence signal during light/heat exposure, then the acquisition of trapped charge during burial over two burial cycles. Sediment deposition and burial allow for the build-up of a trapped charge population because of exposure to ionizing radiation from the surrounding environment and existing cosmic radiation. The luminescence signal measured in the laboratory is related to the time since last exposure to light or heat and the environmental radioactivity at the sample site. From Mahan et al. (2022).
More specifically, De , measured in units of Gray (Gy), is the laboratory radiation dose required to produce a luminescence signal that matches the signal from the natural dose of radiation the target mineral absorbed since last exposure to heat or light. De can be measured from aliquots comprising multiple grains (multi-grain aliquots) or from individual grains of sample using what is known as a SAR protocol. To obtain De from a sample, we apply statistical models to a distribution of De values obtained from these grains or aliquots (Fig. 3). For samples measured at the single-grain level, De distributions commonly include over 100 De values from individual grains.
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Figure 3. Luminescence measurement of multi-grain aliquots of quartz to obtain a De distribution, which is plotted on a radial plot.
Dose rate (Dr) measurement and analysis
The dose rate of the sample and its burial environment is measured in units of Gray per thousand years (Gy/ka). Dr is the rate of exposure of the sample to natural ambient alpha (α), beta (β), and gamma (γ) radiation from the decay of potassium (K), uranium (U), thorium (Th), rubidium (Rb) in the sample and surrounding sediments, and incoming cosmic rays from outer space (Fig. 4). This radiation causes re-mobilization of electrons and their accumulation in structural defects (“traps”) in the crystal lattice of quartz and feldspar grains.
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Figure 4. Sources of radiation in the burial environment and their approximate travel distances. Radiation causes re-mobilization of electrons and their accumulation in structural defects (“traps”) in the crystal lattice of quartz and feldspar grains.
To obtain Dr, we either measure the dose rate directly using radiation detectors (e.g., alpha/beta counting, gamma spectrometry, in situ dosimeters) (Figs 1 & 5), or we measure the concentrations of K, U, Th, and Rb from the sample (e.g., inductively coupled plasma–mass spectrometry/atomic emission spectrometry or ICP-MS/AES, Neutron Activation Analysis or NAA, high-resolution gamma spectrometry) (Fig. 1). We also use established mathematical models to calculate the contribution of cosmic radiation to the sample (Prescott & Hutton, 1994).
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Figure 5. A portable gamma spectrometer is used to measure the ambient gamma radiation at the luminescence sample site.
Data synthesis and interpretation
Once all sample De and dose rate values have been calculated, sample ages are calculated using the age equation above and tabulated. As a form of quality control, final age values are checked against information collected from the site, including its expected age or any independent age control as well as the sample stratigraphic and geomorphic context. Any anomalously large errors are investigated, and if possible, reduced. For a series of samples collected from a vertical stratigraphic sequence, the stratigraphic integrity of the ages are evaluated (i.e., do the ages decrease from bottom to top as expected?). The spread in sample De values is also checked against what is known about the depositional environment of the sample site and sediment transport history.
It’s important to note that in addition to ages, luminescence data can often provide supporting evidence for the site's depositional environment, how the site formed, and the transport history of sediments, rocks, and artefacts. For example, luminescence signals from minerals act like fingerprints that can be matched to the source rock (i.e., the mineral’s provenance: Tsukamoto et al., 2011; Sawakuchi et al., 2019; Gray et al., 2019). Luminescence signals and De distributions can also inform sediment transport dynamics (Brown, 2020; Rhodes & Leathard, 2022) and wildfire intensity (Roose et al., 2020). Luminescence signals measured along the length of rock sample cores can also reveal multiple phases of sun-exposure and burial in a rock or artefact sample, providing insights into its transport history (Freiesleben et al., 2015; Jenkins et al., 2018; Brill et al., 2020; Gliganic et al., 2021).
In-depth analysis of sample luminescence characteristics described above may involve additional research beyond dating. However, luminescence ages and signal characteristics combined with field observations are powerful tools for understanding site formation processes and history. Where possible, all of these factors are considered during the data synthesis and interpretation stage of a project.
Data reporting
Because luminescence dating is an inherently experimental method where new measurement and data analysis procedures are continually being developed and updated, project reports and publications do not follow narrowly defined templates. However, there is some consensus in the luminescence community with regard to reporting and publishing standards. Minimum reporting criteria are tabulated in Table 1.
Table 1. Minimum reporting criteria for luminescence ages. After Mahan et al. (2022).
Primary Reporting Criteria | Supplemental Information |
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Notes: Primary criteria should be included in the main text of the publication, while secondary criteria can be reported in the supplemental material.
Primary criteria listed in Table 1 include the age data (age, De, dose rate, method of De and Dr determination, etc.) that is to be presented within the main text of a report or publication. An example of primary criteria is shown in Table 2. Supplemental information may include supporting data that help explain results and uncertainties (i.e., luminescence decay curves, measurement parameters, dose response curves, De distribution plots, etc.). Often aspects of this supporting data are also discussed in the main text of a report if it shows unique sample characteristics that have a significant bearing on the results.
Detailed definitions and explanations for the reporting criteria listed in Tables 1 and 2 can be found in our Learning Hub as well as our Table of Definitions. It is important to realise that, unlike other dating methods, luminescence ages are conventionally reported at ±1 standard error (σ). Therefore when luminescence ages are compared to radiocarbon ages or other geochronology reported at ± 2 σ, all errors should be adjusted for consistency.
Table 2. Example table for reporting primary luminescence age and dose rate information. After Mahan et al. (2022).
Sample ID | Depth (m) | Water content (wt %) | K (%)1 | Th (ppm)1 | U (ppm)1 | Cosmic dose rate (Gy/ka)2 | Total dose rate (Gy/ka)3 | Numberof aliquots4 | De (Gy)5 | Age (ka)6 |
Unique ID | O.5 | 4.0 | 1.44 ± 0.04 | 3.1 ± 0.3 | 0.8 ± 0.1 | 0.15 ± 0.02 | 1.90 ± 0.10 | 24 (30) | 7.41 ± 0.99 | 3.89 ± 0.27 |
1 Radioelemental determination conducted using inductively coupled plasma–mass spectrometry and inductively coupled plasma–optical emission spectrometry techniques.
2 Cosmic dose rate calculated following Prescott and Hutton (1994).
3 Dose rate calculated using the Dose Rate and Age online calculator (Durcan et al., 2015).
4 Number of aliquots used in age calculation and number of aliquots analysed in parentheses.
5 Equivalent dose (De) calculated using the central age model with 1 standard error (se) uncertainty (Galbraith & Roberts, 2012).
6 Age analysis using the single-aliquot regenerative-dose procedure of Murray and Wintle (2000) on 2 mm small aliquots of 90–150 μm quartz sand.