Aggregation kinetics ofEu2+-cation vacancy dipoles in the alkali halides: Dimer versus trimer formation

The aggregation of ${\mathrm{Eu}}^{2+}$-cation vacancy dipoles in Eu-doped NaCl, KCl, KBr, and RbBr single crystals has been carefully studied by measuring the evolution of dipole concentration as a function of the annealing time at 333, 343, 348, 353, 363, and 373 K using the electron-paramagnetic-resonance technique. The experimentally determined data were analyzed in terms of both pure second- and third-order kinetics equations with back reaction.