TIME-RESOLVED SPECTROSCOPY OF THE EU2-BA2+, EU2+, KCL-SR2+, EU2+ AND KBR-SR2+, EU2+( LUMINESCENCE IN KCL)

In the present paper fluorescence kinetic studies of the Eu2+ luminesc ence in freshly quenched crystals of KCl:Ba2+, Eu2+, KCl:Sr2+, Eu2+ an d KBr:Sr2+, Eu2+ are reported. The measurements were carried out at 30 0 K, at low concentrations of the dopants, and after the crystals were subjected to severe quenching treatments. The results obtained sugges ted that small complexes of Ba2+-Eu2+ are preferentially formed in the lattice of potassium chloride. At variance with this situation, evide nce for the preferential formation of Sr2+-Eu2+ close pairs was not fo und in the doubly doped crystals of KCl:Sr, Eu and KBr:Sr, Eu. These r esults are in good agreement with the ionic radius criterion proposed by Rubio and co-workers several years ago to predict pairing between t wo impurity ions in a solid material.