AbstractThe diffusion of europium was studied in single crystals of potassium chloride by the spectrophotometric method. Measurements were carried out in the temperature range 418–550†C. The absorption spectra as well as the fluorescence spectra of crystals showed that europium diffused in its divalent state, being reduced by the crystal field of potassium chloride. The diffusion of europium can be represented by the equation D = 6.45. 10−2exp(‐29.400/RT). It is concluded that the activation energy consists of the sum of the jump energy of Eu2+and of the enthalpy of solution of EuCl