Concerning infrared-stimulated luminescence from K-feldspars: evidence from heating before stimulating

Repeated heating and stimulation by infrared of feldspar samples causes a reduction in the luminescence signal. Two feldspars were investigated, one microcline and one orthoclase. Empirically the fraction of luminescence signal f(n) remaining after the nth cycle of heating and stimulation is given by f(n)=1−a ln(n) for laboratory dosed samples of both microcline and orthoclase feldspars, for heating temperatures of 150°C, 180°C and 220°C, for heating durations per cycle ranging from 20 s to 2400 s and with the study covering 10 cycles of heating and stimulation. Logarithmic decay of luminescence with time has been explained previously, in other contexts, as due either to quantum tunnelling or to a continuous distribution of states being involved but it is shown that these explanations do not fit the present data. The measured data on f(n) were corrected for the loss of luminescence due to infrared stimulation to ensure that this did not account for the differences between the data and the expectations from models; the functional form f(n)=1−a ln(n) remains valid, although with changed values of a. Numerical simulations of systems involving a limited number of trap depths, from 21 down to 3, were investigated and those with 5 or more trap depths were found to be capable of resembling the data. The simulations could not define a unique pattern of trap depths to match the data, but of the patterns investigated the data were best reproduced by a distribution of at least 5 traps in the energy range from 1.18–1.66 eV. These conclusions augment, and are consistent with, existing information on luminescence mechanisms in potassium-feldspars.