The diffusion of Eu in single crystals was investigated by using a spectrophotometric method which was based upon measurements of the absorption of light with a given wavelength. The data for 418 to 550C could be described by:

D (cm2/s) = 6.45 x 10-2 exp[-29.4(kcal/mol)/RT]

The absorption spectra, as well as the fluorescence spectra, showed that Eu diffused in the divalent state. It was concluded that the activation energy for diffusion was equal to the sum of the jump energy of Eu2+ and of the solution enthalpy of EuCl2.

Diffusion of Divalent Eu into Single Crystals of KCl. R.Reisfeld, A.Honigbaum: Israel Journal of Chemistry, 1968, 6[1], 53-9