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

Abstract

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.

The electronic properties of mixed valence hydrated europium chloride thin film

“…A recent study 12 based on a combination of chemical dosing, core level photoemission spectroscopy, X-ray absorption, and photoluminescence showed that the europium salt prepared following this procedure and placed in an UHV environment presents a homogeneous assembly of hydrated EuCl 2 and EuCl 3 species. Chemical dosing by ionic chromatography leads to a EuCl 2.85AE0.05 composition in good agreement, within measurement accuracy, with electronic properties exhibiting a contribution of 15% o Eu 2+ o 20% and 80% o Eu 3+ o 85% species.…”

“…The determined Eu 2+ : Eu 3+ ratio, although slightly higher than the expected ratio of 15% of divalent europium determined by chemical dosing, remains within the error bar. 12…”

“…11 Recently a stable phase in UHV of a hydrated EuCl 2.85 salt has been evidenced. 12 In general mixed-valence compounds present high interest in electronic applications as fast ion conductors but also mixed ionic-electronic conductors. 13 They notably find applications as solid electrolytes or electrodes in energy storage domains as substituents to liquid electrolytes.…”

“…32,33 Usually, the NEXAFS experiment needs a spectroscopic reference to properly assign the electronic properties and chemical composition of a material. 12,31,34 Here it is shown that the use of the combination of HRPES, NEXAFS and RESPES overcomes this limitation and provides a powerful method to determine both the composition as well as the distribution of various oxides at the surface. 29 In this paper, we report a detailed study on high-resolution 4d photoelectron spectra and resonant soft X-ray 3d -4f and 4d -4f excitations of a hydrated mixed valence europium salt.…”

Control of a two-dimensional molecular structure by cooperative halogen and hydrogen bonds

“…For example, there have been studies on the effect of the halogen bond on 2D self-assembled monolayers, showing that halogen bonds, such as X/X, X/aryl and X/H-C (X: halogen atoms), behave as the primary interactions that control molecular assembly. [18][19][20][21][22][23][24][25][26] However, although research related to 2D molecular self-assembly involving either hydrogen or halogen bonds has already been reported, there have been few experimental studies on 2D molecular self-assemblies formed by both hydrogen and halogen bonds. It is valuable for obtaining the knowledge in the viewpoint of not only fundamental understanding of liquid-solid interface but also further development of 2D molecular assembly.…”