The relationship between thermal activation energy, infrared stimulated luminescence and anomalous fading of K-feldspars

A strong dependence of thermal activation energy (TAE) on infrared (IR) stimulation time for the infrared stimulated luminescence (IRSL) signal was observed for K-feldspar grains extracted from several sediments and granites from China. A TAE value as low as ∼0.1 eV was observed at the beginning of IR stimulation and increased to ∼0.45 eV after 90 s. For a trap depth of ∼2 eV below the conduction band for the IRSL traps, the TAE value of ∼0.45 eV is consistent with the energy gap between the excited states (∼0.5 eV below the conduction band) and conduction band. This phenomenon is explained as the result of the coexistence of thermally assisted recombination via conduction band or band-tail states hopping and athermal tunnelling recombination of electrons from the excited states under IR stimulation, leading to the observation of a higher anomalous fading rate in the initial part of the IRSL decay curve.