Extended Defect Models for Thermoluminescence

Abstract

Thermoluminescence modelling started with very simple models of highly localised point defects, and separation of trapping and recombination centres. Whilst these ideas still dominate the discussions, current research indicates that most defects are far more complex, with localised transitions, and defect interactions extending over many lattice sites. Multi-ion defect sites have been clearly established for LiF dosemeters and, similarly, models to account for charge compensation and lattice distortion of rare earth dopant ions (e.g. in CaF<inf>2</inf>, CaSO<inf>4</inf> etc) all include the possibility of large complex recombination sites. Data obtained from thermoluminescence emission spectra indicate that ions can interact directly by coupling between the trapping and recombination sites. Further, the thermoluminescence dosimetry must originate within different parts of the same large complex. Many examples support models of large complexes with international transitions, including glow peak temperatures which differ with changes in rare earth ion dopants, where the peak shifts are determined by the ionic radii of the rare earth ions. Examples are presented which emphasise that thermoluminescence is often generated by internal charge transfer within very large defect complexes.