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

Open f-shell rare-earth ions doped into a solid state matrix often easily change their charge state via interactions with charge carriers generated by ionizing radiation. This feature promotes a desired efficient radiative recombination of separated charge carriers at rare-earth ion sites but it may also help to stabilize various radiation defects that destructively interfere with the scintillation. The well-known effect responsible for scintillation light loss due to absorptions introduced by these so-called 'radiation damage' centers in alkali halides has been identified and studied for a long time. In this communication we concentrate on a different and much less-known and studied effect in which radiation induced centers directly and actively participate in the scintillation process itself. We present and discuss some selected recent results that illustrate the importance of competition between the prompt radiative recombination via race-earth ions and generation of radiation damage centers in barium fluoride crystals activated with Ce, Pr and Tb. We demonstrate that results of such measurements as radioluminescence spectra, VUV spectroscopy, low temperature thermoluminescence glow curves, isothermal decays, and scintillation time profiles can be consistently explained in the frame of a simple model that includes one recombination 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 creation (equivalent to charge carrier trapping) and thermally activated decomposition (charge carrier release). These effects are shown to account quantitatively for important characteristics of the scintillation process such as large 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 Elsevier Science S.A. All rights reserved.