Uniformity of heating across sample holders during luminescence measurements

For luminescence research, samples are often heated prior to and/or during measurement to measure the thermoluminescence (TL) signal or to remove charge from shallow traps. The reproducibility and repeatability of luminescence measurements will be influenced by how consistently and uniformly the samples are heated, both within a single aliquot and between different readers or sample positions. While the effects of temperature lag during heating have been intensively studied, the spatial uniformity of temperature across samples has received less attention. This study presents spatially-resolved measurements of the temperature of the heating strip, a steel cup and an aluminium single grain disc in a Risø TL/OSL DA20 reader. Temperature is calculated using black body emissions from the three materials, detected with an Electron Multiplying Charge Coupled Device (EMCCD). The results show that temperature is not spatially uniform across any of the three materials, although the degree of variation differs between them. The largest temperature variation is observed across the steel cup (∼18 % at a temperature of 500 °C), followed by the heating strip (∼8 % at a temperature of 500 °C), and then the single grain disc (∼2 % at a temperature of 250 °C). The steel cup also has greater anisotropy in temperature compared to the single grain disc. This study suggests that spatial variation in temperature can be minimised by using sample holders made of materials with high thermal conductivity (e.g. aluminium or silver), and that the impact of thermal variation can be reduced by restricting samples to the central portion of a sample holder (e.g. the central 2 mm of a sample holder (i.e. ‘small aliquots’)).