Measuring photo-transferred thermoluminescence from feldspars in post-IR IRSL procedures using a new user defined command for the Risø TL/OSL reader

Abstract

Stimulating a preheated feldspar sample with infrared light causes photo-transfer of charge within the crystal. The resulting phototransferred luminescence signal is visible in thermoluminescence (TL) and infrared stimulated luminescence (IRSL) measurements, where it results in an increase in the measured luminescence signal intensity. This is particularly relevant when using a post-IR IRSL measurement protocol for dating feldspars, which consists of two consecutive IRSL measurements, one at low temperature (usually at 50 °C) and a second IRSL measurement at elevated temperature. In this case, the lower temperature IRSL measurement causes photo-transfer of charge, which then influences the subsequent higher temperature post-IR IRSL signal. This paper presents a new user defined command to be used with the Sequence Editor software on a Risø TL/OSL reader. This command can be used to assess the amount of photo-transfer that is caused by IR stimulation, and how large a signal this may contribute to a subsequent elevated temperature IRSL measurement. The command can also be useful for identifying the length of time an aliquot should be held at the measurement temperature prior to switching on the IR LEDs in order for any photo-transferred TL to have been reduced to a negligible level. To show the applicability of this new user defined command to feldspar postIR IRSL measurements, this paper presents results from two feldspar samples measured using the new user defined command as part of three different preheat and post-IR IRSL temperature combinations.