Temperature-dependent luminescence of europium aggregates in NaCl

Optical and electron paramagnetic resonance (EPR) spectra of NaCl:Eu2+ crys tals were measured in the temperature between 10 and 300 K. An abnormal tem perature dependence of photoluminescence (PL) associated with the aggregate d europium states was observed in the range from 10 to 100 K. The PL effici ency does nor monotonically vary with temperature, but varies sharply in th e vicinity of 45 and 70 K. Correspondingly. two turning points of EPR inten sity temperature dependence were found at about the same temperatures. The abnormal temperature dependence of luminescence may be explained by the cha nge of nonradiative relaxation rates at different spin ordering states in e uropium chloride aggregates. (C) 2000 Elsevier Science B.V. All rights rese rved.