Radiative recombination in Ce-, Pr-, and Tb-doped barium fluoride

Open f-shell rare-earth ions doped into a solid state matrix often easily c hange their charge state via interactions with charge carriers generated by ionizing radiation. This feature promotes a desired efficient radiative re combination of separated charge carriers at rare-earth ion sites but it may also help to stabilize various radiation defects that destructively interf ere with the scintillation. The well-known effect responsible for scintilla tion light loss due to absorptions introduced by these so-called 'radiation damage' centers in alkali halides has been identified and studied for a lo ng time. In this communication we concentrate on a different and much less- known and studied effect in which radiation induced centers directly and ac tively participate in the scintillation process itself. We present and disc uss some selected recent results that illustrate the importance of competit ion between the prompt radiative recombination via race-earth ions and gene ration of radiation damage centers in barium fluoride crystals activated wi th Ce, Pr and Tb. We demonstrate that results of such measurements as radio luminescence spectra, VUV spectroscopy, low temperature thermoluminescence glow curves, isothermal decays, and scintillation time profiles can be cons istently explained in the frame of a simple model that includes one recombi nation center (RE ion) and a number of charge traps. We find that the trap model of radiation damage centers such as V-k centers describes reasonably well their participation in the scintillation process that includes creatio n (equivalent to charge carrier trapping) and thermally activated decomposi tion (charge carrier release). These effects are shown to account quantitat ively for important characteristics of the scintillation process such as la rge variations in the scintillation light yield with temperature and longer decay times in the scintillation time profiles that effectively lower the scintillation light yield at ambient temperatures. (C) 2000 Published by El sevier Science S.A. All rights reserved.