Injection experiment has been performed to extract injection and photo-currents at constant field stress under different temperature ambient between 795 and 995 K in KCl, KBr and KBr doped KCl single crystals. The variation of the conductivity of injecting carriers with the color centers yielded activation energy value, which is found to have a threshold limit of doping with KBr in KCl matrix. (C) 2003 Elsevier B.V. All rights reserved.