Energy transfer in sodium bromide slightly doped with copper and manganese ions

The optical properties (emission, excitation and lifetime data) of NaBr slightly doped with Cu+ and Mn2+ ions have been studied in the present investigation. The analysis of the spectroscopic data obtained indicated that the Cu+ to Mn2+ energy transfer takes place in this material even at very low impurity concentrations and after the crystals are subjected to severe quenching treatments. This fact suggested that the donor and acceptor ions are not randomly distributed in the lattice of sodium bromide but rather occur as small impurity complexes of Cu+-Mn2+. The data shown in this paper substantiate the ionic radius criterion proposed by Rubio et al., which predicts pairing between two impurity ions in a crystal when their average ionic radius equals the radius of the host ion they replace.