ESR study on impurity-vacancy aggregation in Eu2+ doped and (Eu2+, M2+) doped KCl

The aggregates of Eu2+ ions doped singly or doubly with M2+ (M = Sr, Ca, Cd) in KCl are investigated during aging process of quenched crystals with ESR at 10, 24 and 34 GHz. New ESR spectra are found corresponding to the aggregation stages in KCl: (Eu2+, Sr2+). At 200 to 500 hours after quenching, the ESR signal due to Eu2+ in cubic field appears with the values of g = 2.002, A151 = -32.0 x 10-4 cm-1 and b4sup(o) = 25.9 x 10-4 cm-1, respectively. The spectrum for the final aggregation stage for 1000 hours is accounted for by assuming M2+-vacancy clusters containing several Eu2+-vacancy dipoles and g = 1.990 and b4sup(o) = 620 x 10-4 cm-1, A151 = -32.4 x 10-4 cm-1 are determined. After furter annealing, a broad line with a line width of about 500 oersted appears as the result of the exchange interaction. (author)