UV induced afterglow of KCl : Eu, KBr : Eu and NaCl : Eu at low temperature

摘要

We propose a model for the production of defects by non-ionising radiation in impurity-doped alkali halides based on the formation of impurity-trapped excitons by excitation of the impurity, instead of ionisation of the impurity as has been proposed before. The dissociation of the trapped excitons into F-z and H centres in our model is similar to the case of the formation of F and H centres induced by ionising radiation in pure alkali halides. To gather information about the mechanism of defect creation by non-ionising radiation, we investigate the afterglow (AG) emission induced by UV light at low temperature (20 K) in three different alkali halides KCl, KBr and NaCl doped with Eu impurity. We conclude that the AG emission can be split into two components; one of them has a fast decay and the other one remains for several minutes, decaying according to t(-1/2). This second component has a close relation with the thermoluminescence, emission. We show that the decay of the second component can be explained within the framework of our model if we assume that the H centres migrate along lines. We suggest that these lines are dislocation lines. (C) 2001 Elsevier Science Ltd. All rights reserved. [References: 8]