An overview of, and prospects for, new luminescent detectors

It has been realized since the early development of the first commercial TL dosimeter, LiF:Mg,Ti, that impurities (dopants) play a crucial role in the luminescence process. Initial attempts to describe the mechanisms of TL production were based on the concepts of “point” defects and the interchange of delocalized electronic charge between these defects, which acted either as trapping centers or recombination centers. The mathematics used to describe such processes adopted the decades-old treatments of Randall and Wilkins (1945a,b), Garlick and Gibson (1948), and others, along with suitable assumptions regarding the kinetics of the recombination processes. The modern development of more sophisticated spectroscopic equipment has given a lie to the concept of the “point” defect, however, and TL and OSL processes are now more accurately described in terms of large defect clusters, even including both the trapping site and the recombination site within the same defect complex. Accordingly, alternative charge transport pathways between centers involving localized energy states have to be considered. Such processes impinge directly on our understanding of dose-versus-response functions and other dosimetric properties such as signal fading. Defect clustering also leads to the possibility of “engineering” dosimeters of the future via doping, growth and post-growth processing to create specific defect clusters in order to produce materials with desired dosimetry properties. This paper discusses various aspects of defect clustering and how engineering future luminescence dosimeters might be directed. •TL and OSL dosimetric properties may be improved if recombination processes are local.•Existing sensitive dosimetry materials display localized recombination within large defect clusters.•Linear dose-response characteristics, weak fading and first-order kinetics result.•New dosimetry materials should be grown to induce clustering of traps and recombination centers.