Evidence of Mixed-Valence Hydrated Europium-Chloride Phase in Vacuum by Means of Optical and Electronic Spectroscopies

Studying the optical and electronic properties of commercial hydrated EuCl 3 salts, we took advantage of the manifestation of the unfilled 4f valence shell in photoluminescence and core-level photoemission spectroscopies to unambiguously identify contributions from both Eu 3+ and Eu 2+ configurations. Lanthanide ion salt exhibits sharp spectral lines in good agreement with Eu 3+ oxidized state. Surprisingly, the photoemission spectrum of europium 4d core level presents a singular asymmetric shape component attributed to Eu 2+ species, thus revealing a significant amount of divalent europium. X-ray absorption spectroscopy confirmed the presence of Eu 2+ species in proportions that depend on the origin of the salt and on the applied material processing.