Europium Atoms Research Articles

Magnetic Investigations and 151Eu Mössbauer Spectroscopy of MYbSi4N7 with M = Sr, Ba, Eu

AbstractThe isotypic nitridosilicates MYb[Si4N7] (M = Sr, Ba, Eu) were obtained by the reaction of the respective metals with Si(NH)2 in a radiofrequency furnace below 1600 °C. On the basis of powder diffraction data of MYb[Si4N7] Rietveld refinements of the lattice constants were performed; these confirmed the previously published single‐crystal data. The compounds contain a condensed network of corner‐sharing [N(SiN3)4] units. The central nitrogen thus exhibits ammonium character. Magnetic susceptibility measurements of MYb[Si4N7] (M = Sr, Ba, Eu) show paramagnetic behavior with experimental magnetic moments of 3.03(2), (Sr), 2.73(2) (Ba), and 9.17(2) (Eu) μB per formula unit. In EuYbSi4N7 the europium and ytterbium atoms are in stable divalent and trivalent states, respectively. According to the non‐magnetic character of the alkaline earth cations, ytterbium has to be in an intermediate valence state YbIII‐x in the strontium and barium compound. Consequently, either a partial exchange N3—/O2— resulting in compositions MYbIII‐x[Si4N7—xOx] or an introduction of anion defects according to MYbIII‐x[Si4N7—x/3□x/3] has to be assumed. The phase width 0 ≤ x ≤ 0.4 was estimated according to the magnetic measurements. 151Eu Mössbauer spectra of EuYb[Si4N7] at 78 K show a single signal at an isomer shift of δ = —12.83(3) mm s—1 subject to quadrupole splitting of ΔEQ = 5.7(8) mm s—1, compatible with purely divalent europium.

Full multiple scattering analysis of X-ray absorption near edge structure at the Eu L 3-edge in EuO

X-ray absorption near edge structure (XANES) at the Eu L 3-edge in crystalline EuO is interpreted within full multiple scattering (FMS) formalism. Our theoretical results, based on the ab initio self-consistent (SC) potential calculations, are in good agreement with experimental data. The main features in the experimental signal are reproduced taking into account a cluster of about five coordination shells, centred at the europium atom and having EuO structure. An addition of more distant coordination shells makes features only better resolved. The relatively high intensity of the peak, located just above the Eu L 3-edge, indicates that 5d states are well localised. Comparative analysis with the O K-edge XANES suggests that Eu 5d states are strongly mixed with O 2p states.

The binary gallide Eu 5Ga 9 – crystal structure, chemical bonding and physical properties

The title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K or, alternatively, in glassy carbon crucibles with HF melting. The crystal structure of Eu 5Ga 9 was refined from single-crystal data: Cmcm, a=4.613(1) Å, b=10.902(3) Å, c=26.097(6) Å, Z=4, R F=0.036, 811 structure factors and 46 variables. The structure is described as a three-dimensional network formed by gallium atoms with europium atoms embedded in the cavities. The bonding analysis (LMTO, ELF) confirmed this representation of the structure. Magnetic susceptibility measurements show Curie–Weiss behavior above 60 K with a magnetic moment per Eu atom of 8.12(1) μ B, indicating divalent europium. Eu 5Ga 9 orders antiferromagnetically at 19.0(5) K with re-ordering at 6.0(5) K. The electrical resistivity shows a metallic temperature dependence and magnetic scattering. 151Eu Mössbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting below the ordering temperature.

Crystal Structure of Eu2PdSi3

Single crystals of Eu2PdSi3 were obtained from an arc-melted sample that was further annealed at 1020 K for seven days in a silica tube. The structure of Eu2PdSi3 was refined from single crystal X-ray diffractometer data: P6/mmm, a = 831.88(12), c = 435.88(9) pm, wR2 = 0.1175, 265 F2 values, and 13 variable parameters. It crystallizes with the U2RuSi3 structure, a superstructure of the AlB2 type. The palladium and silicon atoms form a planar two-dimensional [PdSi3] network. The two crystallographically different europium atoms have hexagonal prismatic coordinations Eu1Si12 and Eu2Pd4Si8. The Pd-Si and Si-Si distances within the [PdSi3] network are 244 and 236 pm, respectively.

EXAFS study of the structure of borate-germanate glasses based on an La3Gd10Eu(BO3)6 (GeO4)2O8 solid solution

The nearest environment of europium atoms in borate-germanate glass of composition La3Gd10Eu(BO3)6(GeO4)2O8 was studied by EXAFS spectroscopy, and the Eu-O distances were determined. The structural data on the isostructural compound Gd14(BO3)6(GeO4)2O8 of similar composition were used for the construction of models. It was established that a europium atom is surrounded by eight oxygen atoms, and the Eu-O distance in the glass was equal to ∼2.45 A. These characteristics are close to the values in the crystals of the corresponding solid solutions.

Calculation of the temperature dependence of the work function of an adsorption system

The effect of temperature on an adsorption system was considered in terms of the Anderson-Newns Hamiltonian. Both static effects associated with thermal expansion and the increase of the substrate and adsorbate atomic vibration amplitude with temperature were taken into account. Analytic expressions for the variation of the work function of the system with temperature were derived for the case of low coverages in the linear-in-temperature approximation. The results obtained are compared with experimental data on the adsorption of europium atoms on the (100) surface of tungsten.

Synthesis and electroluminescence properties of an organic europium complex

In order to develop new materials for red electroluminescent devices, a novel ligand, 2-phenyl-imidazo[4,5-f]1,10-phenanthroline (L), and an europium (III) complex with dibenzoylmethanate (DBM), Eu(DBM) 3L, was synthesized. The crystal structure of Eu(DBM) 3L was determined by single crystal X-ray diffraction. The crystal of Eu(DBM) 3L belongs to orthorhombic, space group Pbca with cell dimensions of a=2.1655(6) nm, b=2.0834(5) nm, c=2.6469(7) nm, V=11.942(5) nm 3, Z=8, D x =1.307 g/cm 3. Each europium atom is coordinated with six oxygen atoms from three bidentate DBM anions and two nitrogen atoms from one bidentate L, forming a distorted square antiprism. The complex is easily evaporated and can be used as a red light emitting material. Upon improvement, the device with a structure of ITO/ N, N′-diphenyl- N, N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) (40 nm)/Eu(DBM) 3L (50 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine or BCP) (20 nm)/tris(8-hydroxyquinoline) aluminum (ALQ) (30 nm)/cathode gives off pure red light with luminance of 42 cd/m 2 at 16 V.

Investigation of new odd-parity autoionization Rydberg levels of neutral europium

Transitions to the odd-parity autoionizing energy levels of europium atom from excited states are investigated by the method of two-step laser photoionization. Four new odd-parity autoionizing Rydberg series converging to the first excited ionic level 4f 76s 7S 3 have been discovered in the energy region 45735–47404 cm −1. Sixty-seven new autoionizing levels, which could not be assigned to any of these series, have also been reported. The quantum defects of the Rydberg series show small deviation for lower Rydberg levels indicating inter series interactions or perturbations.

Pressure‐induced Changes of the Crystal Structure of Eu4P3

AbstractPressure‐induced structural changes and electronic properties of rhombohedral Eu4P3 were characterised by means of X‐ray powder diffraction and X‐ray absorption spectroscopy at the Eu LIII threshold. The measurements at low pressures indicate oxidation states of the europium atoms which are compatible with a composition Eu32+Eu3+P3. At a pressure of 8(1) GPa, Eu4P3 undergoes a structural phase transition. The cubic high pressure modification with (anti‐)Th3P4 type crystal structure is also identified as a compound with a non‐integer average oxidation state of the europium atoms.

Crystal chemistry and thermoelectric properties of clathrates with rare-earth substitution

Based on an analysis of the geometric crystallographic relations a general classification scheme is presented for intermetallides with four-coordinated networks isomorphous with hydrate clathrates. We prepared novel europium substituted clathrates, Eu 2− x (Sr,Ba) 6− x M y Si 46− y (M=Al, Ga), consistent with the standardized clathrate I—Ba 8Al 16Ge 30 type structure (space group Pm 3 ̄ n). Europium atoms in Ba compounds preferentially occupy the 2 a position and thus form a new quaternary version of the Ba 8Al 16Ge 30 structure type. All clathrates studied are metals with low electrical conductivity. The negative Seebeck coefficients indicate transport processes dominated by electrons as carriers. Eu 2Ba 6Al 8Si 36 and Eu 2Ba 6Ga 8Si 36 exhibit long-range magnetic order below 32 and 38 K of presumably ferromagnetic type. Magnetic susceptibilities indicate an Eu 2+ ground state, in fine agreement with L III absorption edge spectra.

Temperature dependences in electron-stimulated desorption of neutral europium

The electron-stimulated desorption (ESD) yield for neutral europium (Eu) atoms from Eu layers adsorbed on oxygen-covered tungsten surfaces has been measured as a function of electron energy, europium coverage and degree of oxidation of tungsten, with an emphasis on effects of substrate temperature. The measurements have been carried out using a time-of-flight method and surface ionization detector. We expand on an earlier report, and compare ESD of multivalent Eu with ESD of monovalent alkali atoms, studied previously. The Eu atom ESD is a complicated function of Eu coverage, electron energy and substrate temperature. In the coverage range 0.05–0.35 monolayer (ML), overlapping resonant-like Eu atom yield peaks are observed at electron energies E e of 36 and 41 eV that might be associated with Eu or W shallow core level excitations. Additional resonant-like peaks are seen at E e of 54 and 84 eV that are associated with W 5p and 5s level excitations. The Eu atom yield peaks at 36 and 41 eV are seen only in the temperature range 220–300 K in a narrow europium coverage range (0.07–0.35 ML), and the temperature range becomes narrower with increasing europium coverage. In contrast, the peaks at 54 and 84 eV persist above 500 K over a wide coverage range. It is possible that the yield associated with the tungsten core level excitations may arise from the ESD of EuO molecules rather than Eu atoms. This is the only reported system for which the electron energy dependence of neutral ESD yield has a resonant character, in the absence of a non-resonant background.

Cross Sections of Excitation of Resonance Transitions of EuI by Electron Impact

The excitation of resonance transitions of a europium atom by electron impact is investigated using the method of extended crossing beams. Comparison of the obtained results with data of previous investigations shows that the form of the optical excitation functions is in good agreement with the experimental data but differs considerably from the theoretical ones. The absolute values of cross sections at the electron energy of 100 eV are close to predicted values and exceed the data of the previous experiment by two orders of magnitude.

Supramolecular formation by aromatic ring stacking and hydrogen bonding in lanthanide(III) complexes with amino acids and 1,10-phenanthroline

[Eu(ABA)(phen) 2(H 2O) 3](ClO 4) 3·3phen·4.5H 2O (1) and [Eu(Val)(phen) 2(H 2O) 3](ClO 4) 3·3phen·2H 2O (2) are two new europium complexes with amino acids and 1,10-phenanthroline (phen=1,10-phenanthroline, ABA=α-amino butyl acid, Val= l-valine). Their crystal structures were measured by X-ray crystallography. Europium atoms in both complexes are nine-coordinated with bidentate 1,10-phenanthroline and carboxylate anion of amino acids, and water molecules. In the solid state, 1 and 2 have a structure involving aromatic stacking of the coordinated and non-coordinated 1,10-phenanthroline and the oxygen atoms of non-coordinated perchlorate anions being H-bond acceptors connect [Eu(ABA)(phen) 2(H 2O) 3] 3+·3phen·4.5H 2O or [Eu(Val)(phen) 2(H 2O) 3] 3+·3phen·2H 2O in their structures. In their interactions, several C–H⋯O bonds play an important role. Owing to their different amino acid ligands and the number of lattice water molecules, there is some difference in their hydrogen bond patterns in 1 and 2. The side chain of l-valine is involved in the formation of C–H⋯O bonds. Hydrogen bond and π–π interactions determine the supramolecular formation of three-dimensional net works of both complexes.

Study on highly ordered luminescent Langmuir–Blodgett films of heteropolytungstate complexes containing lanthanide

Luminescent thin films of heteropolytungstate complexes containing lanthanide (europium or samarium) were successfully fabricated by the Langmuir–Blodgett (LB) technique. The pressure–area isotherm of the monolayer of dimethyldioctadecylammonium bromide (DODA) is modified rather markedly when the subphase contains the complex of Na 9EuW 10O 36 or Na 9SmW 10O 36. The above results indicate that the monolayer of DODA has a strong interaction with the polyanions of EuW 10O 36 9− (or SmW 10O 36 9−). X-ray photoelectron spectra and fluorescent spectra verify that europium and tungsten atoms are incorporated into the LB films. Ultraviolet (UV), fluorescent spectra and low-angle X-ray diffraction experiments demonstrate that these LB films have a well-defined lamellar structure. The LB film containing EuW 10O 36 9− can give off strong fluorescence on UV irradiation. The characteristic emission behaviors of europium ions in LB films and in the powder of Na 9EuW 10O 36 are discussed. It is found that the intensity ratio of the 5D 0→ 7F 2 transition to the 5D 0→ 7F 1 transition in LB film is quite different from that in the powder of Na 9EuW 10O 36. The difference of the ratio indicates that the site symmetry of europium is distorted in LB film, which is probably due to the strong electrostatic interactions between DODA and polyanions.

Study of europium traces by laser resonance ionization spectroscopy

A three-stage scheme for the excitation of the autoionization state of europium atoms is realized, and the corresponding ionization cross section is determined: σ=6.5×10−10 cm2. Analytical signals from europium atoms are recorded in standard and waste water solutions used in mining noble metals and in the diagnostics of rare-earth elements.

Crystal Structure and Luminescence of a Europium Coordination Polymer { [Eu(p‐MOBA)3 · 2H2O] · 0.5H2O · 0.5 (4, 4′‐bipy) } ∞

AbstractThe structure of the complex { [Eu (p‐MOBA)3 · 2H2O] · 0.5H2O·0.5(4,4′‐bipy)}∞ (p‐MOBA: p‐methoxybenzoate, 4,4′‐bipy: 4,4′‐bipyridine) was determined by single crystal X‐ray diffraction study. Each europium atom is coordinated with two oxygen atoms of the chelated carboxyl group, four oxygen atoms of the four bidentate bridging carboxylate groups and two oxygen atoms of two water molecules, forming an infinite polymeric chain structure. Excitation and luminescence spectra were observed at 77 K. The high resolution spectrum of the complex shows that the europium ion site in the crystal has low symmetry. The complex displays intense luminescence which may be related to the p‐MOBA ligand and the polymeric coordination.

Mössbauer studies and magnetic properties of the novel ternary europium pnictides LiEuPn (Pn=P, As, Sb, Bi) with TiNiSi type structure

Abstract 151Eu Mossbauer studies and magnetic susceptibility measurements of novel ternary europium pnictides LiEuPn (Pn=P, As, Sb, Bi) have shown that the majority of europium atoms is divalent in these materials and that there is magnetic ordering at low temperatures. For the four compounds with TiNiSi structure, from Pn=P to Bi, the EuEu distances increase and ferromagnetic couplings decrease in favour of antiferromagnetism. The magnetic flux density of the hyperfine field at 151Eu is proportional to the isomer shift. Its temperature dependence cannot be explained in terms of a simple molecular field model.

Ferromagnetism and giant magnetoresistance in the rare-earth fulleridesEu6−xSrxC60

We have studied crystal structure, magnetism, and electric transport properties of a europium fulleride ${\mathrm{Eu}}_{6}{\mathrm{C}}_{60}$ and its Sr-substituted compounds, ${\mathrm{Eu}}_{6\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{C}}_{60}.$ They have a bcc structure, which is an isostructure of other ${M}_{6}{\mathrm{C}}_{60}$ $(M$ represents an alkali atom or an alkaline-earth atom). Magnetic measurements revealed that magnetic moment is ascribed to the divalent europium atom with $S=7/2$ spin, and a ferromagnetic transition was observed at ${T}_{C}=10--14\mathrm{K}.$ In ${\mathrm{Eu}}_{6}{\mathrm{C}}_{60},$ we also confirm the ferromagnetic transition by heat-capacity measurement. The striking feature in ${\mathrm{Eu}}_{6\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{C}}_{60}$ is very large negative magnetoresistance at low temperature; the resistivity ratio $\ensuremath{\rho}(H=9\mathrm{T})/\ensuremath{\rho}(H=0\mathrm{T})$ reaches almost ${10}^{\ensuremath{-}3}$ at 1 K in ${\mathrm{Eu}}_{6}{\mathrm{C}}_{60}.$ Such large magnetoresistance is the manifestation of a strong $\ensuremath{\pi}\ensuremath{-}f$ interaction between conduction carriers on ${\mathrm{C}}_{60}$ and $4f$ electrons of Eu.

XAFS at Eu–L 3 edge and UV–VUV excited luminescence of europium doped strontium borophosphate prepared in air

The local structure and the valences of europium in SrBPO 5:Eu prepared in air were checked by means of XAFS at Eu–L 3 edge. From the EXAFS results, it was discovered that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu–O were 2.42 Å in the host. From the XANES data, it was found that the divalent and trivalent europium coexisted in the matrix. The emission spectra excited by VUV or UV exhibited a prominent broad band due to the 4f 65d–4f 7 transition of Eu 2+ ions, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [V Sr]″ formed by aliovalent substitution between Sr 2+ and Eu 3+ ions. The VUV excitation spectra in 100–200 nm range showed that the matrix had absorption bands with the maxima at about 130 and 150 nm, respectively.

Palladium-Cadmium Ordering In Repdcd (Re = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb) And Comparison With Isotypic Indium Compounds

Abstract Ternary intermetallic compoundsREPdCd (RE=La, Ce, Pr, Nd, Sm, Eu, Tb)were synthesized by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. All compounds were investigated by X-ray diffraction on powders. Those with RE = La, Ce, Pr, Nd, Sm, and Tb contain trivalent rare earth metals and they crystallize with the hexagonal ZrNiAl type structure. NdPdCd [a = 764.8(3), c = 401.3(2) pm] and TbPdCd [a = 756.5(2), c = 389.0(1) pm] are reported here for the first time as well as EuPdCd. The compounds with La, Ce, Pr, and Sm [J. Alloys Compd. 182, 87 (1992)] are confirmed. The crystal structure of EuPdCd was refined from X-ray single crystal diffractometer data: TiNiSi type, Pnma, a = 745.9(3), b = 439.8(2), c = 863.7(3) pm, wR2 = 0.0405, 683 F2 values, and 20 variable parameters. The three-dimensional [PdCd] substructure consists of strongly puckered, orthorhombically distorted Pd3Cd3 hexagons with Pd-Cd distances ranging from 283 to 285 pm. The europium atoms fill the cavities within the [PdCd] network. Chemical bonding in the series REPdCd and REPdIn is compared.