Fluorescence kinetic studies were made of the Eu2+ luminescence of freshly-quenched crystals of material which had been doped with Ba2+, Eu2+ and/or Sr2+. The measurements were carried out at 300K, using low concentrations of the dopants, and the crystals were then subjected to severe quenching. The results suggested that small complexes of Ba2+-Eu2+ formed preferentially in the KCl lattice. On the other hand, no evidence was found for the preferential formation of Sr2+-Eu2+ close pairs in doubly-doped crystals of KCl or KBr. The results were in good agreement with an ionic radius criterion which had been proposed for the prediction of pairing between 2 impurity ions in solids.

R.F.Sosa, E.R.Alvarez, M.A.Camacho, A.F.Muñoz, J.O.Rubio: Journal of Physics - Condensed Matter, 1995, 7[32], 6561-7