Recent advances in the theory of thermoluminescence and optically stimulated luminescence; Delocalized transitions

Several theories explain different facets of the phenomena of thermoluminescence (TL) and optically stimulated luminescence (OSL). In the present chapter we concentrate on models dealing with processes occurring when charge carriers are moving between traps and centers through the conduction and valence bands. The processes involved include transitions occurring during excitation and during read-out: optical stimulation in OSL and heating in TL. Older theories explaining the basic properties of first-and second-order kinetics as well as the effects of non-linear dose dependence of TL and OSL are briefly mentioned. More recent models, developed in the last decade are described in more detail. The effects of competition between traps and between centers both during excitation and read-out are discussed in some detail, yielding the interpretation of superlinear dose dependence, non-monotonic dose dependence as well as dose-rate dependence. The theories can also explain the experimentally observed concentration quenching and the prevalence of first-order peaks in various materials. A model for explaining an anomalous heating-rate effect and thermal quenching is discussed. The occurrence of anomalously high or low activation energies and frequency factors, sometimes evaluated by standard peak-shape methods is also briefly discussed. Finally, the recently studied subject of two-electron traps or two-hole centers and their effects on TL and OSL phenomena are discussed.