Eu L3 Research Articles

Neutron Reflectivity for Testing Graphene Oxide Films Sorption of EuCl3 in Ethanol Solution

Neutron reflectivity (NR) was used to study the sorption of Eu(III) by graphene oxide (GO) films exposed to ethanol solution of EuCl3. Most of the earlier sorption studies have been performed using GO dispersed in solution. In contrast, layered structure of GO films imposes limitations for penetration of ions between individual sheets. The analysis of NR data recorded before and after sorption under vacuum demonstrates an increase of GO film thickness due to sorption by 35–40%. The characterization of chemical state of Eu(III) sorbed by GO films by X‐ray absorption near‐edge structure (XANES) in high‐energy resolution fluorescence detection (HERFD) method at the Eu L3 edge reveals that it remains the same as in anhydrous EuCl3. Analysis of all collected data including reference experiments with bulk GO samples allows to conclude that EuCl3 penetrates into GO interlayers with ethanol solution and remains trapped in interlayers after evaporation of ethanol. Sorption of EuCl3 results in nearly complete amorphization of film and likely formation of voids, thus making NR models based on specific volume of unit cell not valid for quantitative evaluation of Eu sorption. Limitations of NR method must be taken into account in future studies of sorption by thin films.

Pressure evolution of electronic and crystal structure of noncentrosymmetric EuCoGe3

We report on the pressure evolution of the electronic and crystal structures of the noncentrosymmetric antiferromagnet EuCoGe3. Using a diamond anvil cell, we performed high pressure fluorescence detected near-edge x-ray absorption spectroscopy at the Eu L3, Co K, and Ge K edges and synchrotron powder x-ray diffraction. In the Eu L3 spectrum, both divalent and trivalent Eu peaks are observed from the lowest pressure measurement (~2 GPa). By increasing pressure, the relative intensity of the trivalent Eu peak increases, and an average Eu valence continuously increases from 2.2 at 2 GPa to 2.31 at~50 GPa. On the other hand, no discernible changes are observed in the Co K and Ge K spectra as a function of pressure. With the increase in pressure, lattice parameters continuously decrease without changing I4mm symmetry. Our study revealed a robust divalent Eu state and an unchanged crystal symmetry of EuCoGe3 against pressure.

Energy Transfer from Antenna Ligand to Europium(III) Followed Using Ultrafast Optical and X-ray Spectroscopy.

A series of highly luminescent europium(III) complexes which exhibit photoluminescence from the Eu(III) center following energy transfer from the UV absorbing organic sensitizer have been investigated using a combination of ultrafast optical transient absorption and Eu L3 X-ray transient absorption techniques. We have previously demonstrated that the latter can be used as a signature of 4f-4f excitation responsible for the photoluminescence in these Eu(III) coordination complexes, but the long time scale of the earlier measurements did not allow direct observation of the ligand-to-metal energy transfer step, preventing a determination of the sensitization mechanism. Here, we provide the first direct experimental verification that Dexter electron exchange from the ligand triplet state is the dominant energy transfer mechanism in these photoluminescent systems. Moreover, the optical transient absorption results obtained herein imply that energy transfer for all three compounds has near unity yield, regardless of differences in the sensitization efficiencies, suggesting that the variations in the sensitization efficiencies are determined almost entirely by differences in the ligand-centered intersystem crossing rates. The implications for the rational design of more effective photoluminescent lanthanide complexes are discussed.

X-ray spectral diagnostics of synthetic lanthanide silicates

Potassium and rare-earth (Eu, Sm, Yb, Ce) silicate and aluminosilicate crystals are hydrothermally synthesized under isothermal conditions at 500°C and a pressure of 100 MPa. The chemical and structural formulas of the synthesized compounds HK6Eu[Si10O25], K7Sm3[Si12O32], K2Sm[AlSi4O12] · 0.375H2O, K4Yb2[Si8O21], and K4Ce2[Al2Si8O24] are determined. In addition, a synthesis product with Eu, in which the dominant phase is assumed to be K3Eu3+[Si6O15] · 2H2O, is studied. The oxidation state of lanthanides in the silicates under study is determined based on X-ray absorption near-edge structure spectroscopy. The Eu L3-, Sm L3-, Yb L3-, and Ce L3-edge X-ray absorption spectra of the studied silicates and reference samples are recorded using a Rigaku R-XAS laboratory spectrometer. As reference samples, Eu2+S, Eu3+F3, Eu23+O3, Sm23+O3, Yb23+O3, Yb3+F3, Yb3+Cl3, Ce23+O3, and Ce4+O2 are used. Comparison of the absorption edge energies of lanthanide silicates and reference samples shows that Eu, Sm, Yb, and Cе in all the samples studied are in the oxidation state 3+. The synthesized silicates will supplement our knowledge of possible rare-earth minerals existing in hydrothermal systems, which is important for analyzing the distribution spectra of rare elements, which are widely used for diagnostics of geochemical processes and determination of sources of ore materials.

Local structure and structural rigidity of the green phosphor β-SiAlON:Eu2+

Eu2+ inserted in β-Si3−xAlxOxN4−x is a material that shows exceptional promise as a green-emitting phosphor. Synchrotron X-ray and neutron scattering, in conjunction with first-principles calculations and Eu L3 X-ray absorption measurements, yield a consistent picture of the composition, and the favorable position for Eu2+ substitution in the crystal structure. The Debye temperature Θ D, which is a proxy for structural rigidity relating to effectiveness as a phosphor, is very high for the starting β-Si3N4 framework and is determined to decrease only slightly for the small amounts of Al3+ and O2− co-substitution that are required for charge balance associated with Eu2+ insertion.

Direct Observation of 4f Intrashell Excitation in Luminescent Eu Complexes by Time-Resolved X-ray Absorption Near Edge Spectroscopy

We report time-resolved X-ray absorption near edge structure (TR-XANES) measurements at the Eu L3 edge upon photoexcitation of several Eu(III)-based luminescent lanthanide complexes. We find an unambiguous signature of the 4f intrashell excitation that occurs upon energy transfer from the photoactive organic antennas to the lanthanide species. Phenomenologically, this observation provides the basis for direct investigation of a crucial step in the energy transfer pathways that lead to sensitized luminescence in lanthanide-based dyes. Interestingly, the details of the TR-XANES feature suggest that the degree of 4f-5d hybridization may itself vary depending on the excited state of the Eu(III) ion.

Resonant X-ray diffraction of self-assembled epitaxial systems: From direct to complementary chemical information

In this work we depict schematically the use of resonant (anomalous) X-ray diffraction as a tool to directly probe strain and composition of self-assembled semiconductor islands. By employing a direct analysis at the Eu L3 edge its composition gradient is quantified for EuTe:SnTe capped islands. Projection maps are proposed to visualize the results, providing an alternative capability to infer quantum dot properties. A more complex methodology is applied to the study of InP:GaAs islands, in which complementary anomalous measurements are performed. For this system the number of samples analyzed allows us to extract the activation energy for Ga adatoms diffusion from the substrate to the islands.

EuFe2As2: Magnetic Structure and Local Charge Distribution Anisotropies as Seen by Resonant X-ray Scattering

Non-resonant and element specific magnetic X-ray scattering has been used to determine the orientation of Eu and Fe magnetic moments in EuFe2As2 iron pnictide. Experiments have been carried out on single crystal samples at the ESRF. Resonant measurements on magnetic reflections at the Eu L3 absorption edge indicate that the orientation of the Eu moments in the antiferromagnetic phase (T<T N=19 K) lie parallel to the crystallographic a-axis. In addition, non-resonant magnetic X-ray measurements indicate that the Fe moments are aligned along the same direction in the spin density-wave ordered phase (T<T S=190 K). The temperature dependence of the integrated intensities suggests that the Fe magnetic sublattice is barely affected by the onset of Eu ordering at T N. The observation of non-zero resonant intensity on nuclear-forbidden reflections with wavevector corresponding to the Fe magnetic propagation vector at both the Eu L3 and As K absorption edges may be interpreted as the result of the polarization of the Eu 5d and As 4p electronic bands via hybridization with the Fe 3d states.

Ferrimagnetism inEuFe4Sb12due to the Interplay off-Electron Moments and a Nearly Ferromagnetic Host

We combine x-ray magnetic circular dichroism spectroscopy at Fe L2,3 edges, at Eu M4,5 edges, x-ray absorption spectroscopy (XAS) investigation of Eu valence, and local spin density calculations, to show that the filled skutterudite Eu0.95Fe4Sb12 is a ferrimagnet in which the Fe 3d moment and the Eu2+ 4f moment are magnetically ordered with dominant antiferromagnetic coupling. From Eu L3 edge XAS, we find that about 13% of the Eu have a formal valence of 3+. We ascribe the origin of ferrimagnetism at a relatively high transition temperature TC of 85 K in Eu0.95Fe4Sb12 to f-electron interaction with the nearly ferromagnetic [Fe4Sb12]2.2- host lattice.

Local Structure of Nanocrystalline Lu2O3:Eu Studied by X-ray Absorption Spectroscopy

Eu-doped nanocrystalline Lu2O3 with different particle sizes was prepared by combustion synthesis. The local structures around the rare-earth Lu and Eu ions were studied by using both Lu and Eu L3 ...