Charge transport in band-tail states of irradiated alkali feldspar I: Super-Arrhenius kinetics

Abstract

Infra-red stimulated luminescence (IRSL) emission in alkali feldspar comprises two components that arise due to tunneling from the excited state of the primary IRSL trap and the band tail states of the host material. Combination of two Becquerel functions fit well to the IRSL decay curve. The second component which has a longer lifetime was identified with that of the excited state tunneling and found that is dominated at the later part of the decay curve. This part was removed from the IRSL signals to isolate the signals that were predominantly of band tail transport. IRSL decay curves measured at various temperatures from 50 °C to 250 °C after preheated to 280 °C, were fitted to Becquerel function. From the Becquerel function, time-dependent decay rates and the distribution of decay rates were extracted. Ensemble average decay rates were calculated from the distribution of decay rates and found they increase with stimulation temperature. IRSL intensity exhibits a similar behavior. Both were yielding diminishing returns at higher temperatures. Hence, both exhibited a non-linearity in Arrhenius plots. These non-Arrhenius data were analyzed using the deformed exponential function, and that yielded a temperature dependent (decreasing from ∼0.12 eV to ∼ 0.02 eV, with temperature) thermal activation energy. At lower temperature, larger thermal energy is needed to activate the charge transport at lower mobility band tail states, and smaller energy is sufficient at high mobility states. Assuming the processes that are responsible for IRSL intensity change and decay rate change with temperature are different, IRSL intensity change was analyzed using the combination of thermal assistance and thermal quenching. The thermal activation energy of 0.22 eV was obtained for quenching, and it is also observed that the quenching doesn't happen at the recombination center but elsewhere.