Tunnelling in Afterglow: its Coexistence and Interweaving with Thermally Stimulated Luminescence

After irradiation of a phosphorescent material, the intensity of the afterglow is usually strongly dependent on the temperature: as lower temperatures are reached, it drops below the noise. But sometimes this intensity stops dropping and becomes stationary. It is seen then to decrease slowly with the time t with (1/t) kinetics. This odd emission is shown to compete with the regular TL or OSL by involving the same traps and centres. It is proposed that in this process the trapped charges recombine with centres without thermal excitation by tunnelling through a potential barrier. The parasitical effect of anomalous fading in radiation dosimetry and dating, with its experimental logarithmic law of loss of stored TL, is shown to be explained by this tunnelling. This effect, together with widening of TL peaks, turns up in samples which have less perfect or disordered crystal lattices.