Optically stimulated phosphorescence in orthoclase feldspar over the millisecond to second time scale

In the past, time-resolved IR stimulated luminescence (TR-IRSL) curves from feldspar have mainly been measured over a few hundred μs with the purpose of estimating the lifetimes of the components. In this study, we present the decay form of time-resolved IRSL and IR stimulated phosphorescence (IRSP) from orthoclase feldspar covering over 8 orders of magnitude (50 ns to 7 s). A detailed characterisation of the slowly decaying signals (ms to s time scales) from feldspar is undertaken to obtain further insight into the role of re-trapping in both the IR stimulated luminescence (IRSL) and the relatively more stable post-IR IRSL signals. The decay form of the different signals examined here shows a weak dependence on preheat temperature and a strong dependence on stimulation temperature. Interestingly, the IRSP curves show a conspicuous kink of which the position is linearly dependent on the on-time duration. The data on thermal dependence of these signals might suggest that the decay behaviour of the time-resolved IRSL and phosphorescence signals mainly reflect the occupancy of electrons in the band tail states with a significant contribution from the shallow traps. This interpretation is supported by thermoluminescence (TL) curves showing the photo-transfer effect during short IR and post-IR IR stimulations.