An investigation of ESR signals and their related TL emission in speleothem calcite

Abstract

TL emission spectra were recorded using a sensitive Fourier transform spectrometer for 4 samples of speleothem calcite which had been selected to display a range of ESR signals. Two samples showed principal emissions at 610 nm for both the 160°C and 270°C TL peaks which are attributed to Mn-related luminescence centres, while the remaining two samples had their principal emissions at 480 and 580 nm, which is characteristic of Dy-related luminescence centres. The relative intensities of the TL emission and ESR signals within individual samples, and between those having the same luminescence centres, together with kinetic studies infer correlations between the g = 2.0036 ESR signal and TL emission at 220°C, and the 160°C TL peak and the g = 1.9975 ESR signal. The g = 2.0005 signal used for dating appears to correspond with the 270°C TL peak, but at elevated temperatures the mean life of the latter is significantly less than that of the ESR signal. This could be explained if the luminescence centres have a lower stability than the trap sites measured directly by ESR. All correlations should be treated with caution because charge may be lost from ESR traps via different routes in each calcite, giving wide variations in luminescence efficiency.