Monte Carlo simulations of tunneling phenomena and nearest neighbor hopping mechanism in feldspars

Abstract

The study of luminescence signals from geological materials is of importance in dosimetric and dating applications. Monte Carlo simulations are often used to describe the charge creation, charge trapping and donor/acceptor recombination processes in luminescent and dosimetric materials. While such stochastic methods are in wide use in many applied areas of physics, there have been few studies of such phenomena on the origin and production of luminescence signals for feldspars, apatites and similar materials exhibiting loss of charge due to quantum tunneling phenomena. Previous Monte Carlo work on feldspars has been based on the assumption that the number density of donors and acceptors are equal at any time. These previous studies were able to get good agreement with experiment only when they assumed that the crystal consisted of small sub-volumes, and that charge carriers were only allowed to recombine within these nanocrystals. This paper provides a different version of this previously suggested model, in which the number density of acceptors far exceeds that of donors. The new version of the model describes the loss of charge due to ground state tunneling, as well as the charge creation by natural irradiation of samples. The results from the model compare well with previously derived approximate analytical equations for feldspars. In addition, the Monte Carlo simulations provide valuable insight into the various factors which affect the luminescence mechanism in these materials. The simulations can describe the loss of charge on a wide variety of time scales, from microseconds to thousands of years. The effect of crystal size, charge carrier density, natural irradiation dose rate and total number of charge carriers is studied in a quantitative manner. Finally we examine the possibility of extending the present version of the model to describe luminescence signals originating in the nearest neighbor hopping mechanism in feldspars. The results from the model are compared with experimental data from time-resolved infrared stimulated luminescence (TR-IRSL) in these materials.