Europium Atoms Research Articles

Spin–disorder scattering in europium-doped indium antimonide thin films

We have studied the low temperature magnetoresistance of In1−xEuxSb for a range of europium concentrations. We find that the addition of the rare earth element reduces the carrier mobility substantially and alters dramatically the character of the magnetoresistance. In particular, we observe negative magnetoresistance for 0.012<x<0.05. We attribute this to a predominance of scattering of the conduction electrons by the magnetic spins of the europium atoms, a scattering process which becomes less effective as the spins align with the magnetic field. For the most lightly doped sample, the magnetoresistance becomes positive at high fields, indicating complete saturation of the spin alignment and appearance of normal (classical) magnetoresistance. In addition, for samples not too heavily doped with europium, the magnetoresistance for very low fields (less than 0.5 T) is small and positive before reaching a maximum and evolving into a negative magnetoresistance. This behavior, similar to that seen in EuSe, is thought to be due to a redistribution of the conduction electrons in the spin–split electronic energy levels.

Resonance fluorescence in radiative collisions: Theoretical study of the spectral line shapes.

We describe the spectral properties of the resonance fluorescence emitted in radiative collisions. The line shapes of the anelastic components of the spectrum are found to be strongly asymmetric, with extended wings related to the van der Waals shift of atomic levels. The specific case of europium and strontium atoms is considered for a combined collisional-radiative interaction following adiabatic dynamics.

Synthesis and infrared and Mössbauer studies of Eu(III) complexes with cyanoxime anions

A series of europium(III) complexes with cyanoxime ligands were prepared. The IR spectroscopic data revealed that the ambidentate ligands were coordinated to the central europium(III) atom in either a tridentate or a bidentate manner. The Mössbauer isomer shift ( IS) values showed a correlation with the quadrupole splitting ( QS) values in all complexes. A plot of the IS values versus the QS values showed that with increasing electron density of the Eu(III) nucleus the symmetry of the electronic shell around the Eu(III) atom decreases.

Resonance structure due to the 4d104f7-->4d94f8 transition in the photoionization cross section of atomic europium.

Photoionization cross sections for the 4d, 4f, 5s, 5p, and 6s electrons and angular-distribution asymmetry parameters for the 4d, 4f, and 5p electrons of atomic europium at photon energies near the 4${\mathit{d}}^{10}$4${\mathit{f}}^{7}$\ensuremath{\rightarrow}4${\mathit{d}}^{9}$4${\mathit{f}}^{8}$ resonance have been calculated by use of many-body perturbation theory. Interactions among ionization channels were included in the calculation, and the results are compared with experiments and other calculations.

M�ssbauer study of mixed-ligand complexes of europium(III)

A series of europium(III) mixed complexes was prepared containing 1,10-phenanthroline or 2,2′-bipyridine as neutral ligand and simple inorganic anions or benzoate and its derivatives as ionic ligands. The Mossbauer spectra of the products indicated that both types of ligands were directly coordinated to the central europium(III) atom. The Mossbauer isomer shift values reflected both electron shifting and steric effects of the substituents on the ligand. The quadrupole splitting values pointed to the similar symmetry of the electron shell of the europium in almost all complexes with analogous composition. The IR spectra provided evidence of the binding mode of the carboxylate groups in the complexes containing benzoate or its derivatives. The x-ray photoelectron spectra of the compounds demonstrated the effects of electrophilic and nucleophilic substituents on the electron binding energies in the europium, oxygen, and nitrogen orbitals.

Study of the Mössbauer effect of europium orthophosphate crystals

The Mössbauer spectra of europium orthophosphate crystals were measured. The isomer shift (IS), the component V zz of the electric field gradient, the electric quadrupole splitting component eQV zz and the asymmetry parameter η were determined. The contributions of the crystal field and the valence electrons to the electric field gradient were calculated. The results show that there may be some electron populations in the 5d valence orbitals of the europium atom and that the chemical bond between the europium atom and the nearest oxygen atoms may possess a certain covalent character.

Lanthanide ion complexes of the calixarenes. Part 4. Double inclusion by p-t-butylcalix[4]arene (H4L). Crystal structures of [Eu2(HL)2(dmf)4].7dmf (dmf = dimethylformamide) and H4L.dmso (dmso = dimethyl sulphoxide)

Reaction of europium(III) with p-t-butylcalix[4]arene (H4L) under the same conditions as used for reactions with larger calixarenes yields a yellow crystalline complex structurally characterised as [Eu2(HL)2(dmf)4].7dmf, where dmf =N,N-dimethylformamide. The crystals are monoclinic, space group C2/c with a= 35.03(2), b= 16.12(2), c= 23.38(2)Å, β= 98.40(4)°, and Z= 4 dimers; the structure was refined to R= 0.096 for 9 248 ‘observed’ reflections. The complex is binuclear and centrosymmetric with the europium atoms bridged by one phenoxide group from each calixarene ligand and each europium being bound to two unidentate dmf ligands as well as the three other phenolic oxygens of a calixarene ligand. The calixarene ligands adopt a distorted ‘cone’ conformation in which a dmf molecule is included but in such a manner that there is clearly no co-ordinate interaction with europium. The same type of inclusion is found in the dimethyl sulphoxide (dmso) adduct of p-t-butylcalix[4]arene, H4L·dmso, this compound having been used in ligand purification. It forms large tetragonal crystals, space group P4/n, a= 12.811(4), c= 13.082(4)Å; R= 0.11 for 895 ‘observed’ reflections.

Lanthanoid-olefin complex formation: a matrix-isolation ultraviolet-visible and infrared study of the direct synthesis of (C2H4)nEu using europium atoms

Eu(C/sub 2/H/sub 4/)/sub n/ complexes have been synthesized at 12 K by codepositing Eu atoms with ethylene, neat or doped in Ar or Xe. UV-visible absorption spectroscopy of the highest stoichiometry product revealed a broad, intense visible transition centered at 537 nm. The complex is unstable above 50 K, consistent with the absence of any evidence for reaction in 77 K metal vapor reactions. Optical spectroscopy of the products formed in dilute matrices indicated the formation of a lower stoichiometry Eu-C/sub 2/H/sub 4/ complex. This was confirmed by infrared studies of absorption in the coupled ..gamma..(C=C)delta(CH/sub 2/) region. Under high dilution conditions, a matrix split 11981182 cm/sup -1/ doublet is assigned to a monoethylene europium ..pi.. complex. Matrix-annealing experiments combined with EuC/sub 2/H/sub 4/ reactions in C/sub 2/H/sub 4/rare-gas matrices of increasing C/sub 2/H/sub 4/ concentration trace the conversion of Eu(C/sub 2/H/sub 4/) to the highest stoichiometry species absorbing at 1233 cm/sup -1/. In general, the Eu(C/sub 2/H/sub 4/)/sub n/ IR spectra are similar to those of matrix-isolated group VIII (8-10) and IB (11) ethylene ..pi.. complexes.

Coordination Chemistry of the Calixarenes. II. Europium(III) and p-t-Butyl Calix[6]arene

The possible nature of p-t-butyl-calix [6] arene complexes of lanthanide elements has been explored by determination of the single-crystal X-ray structure of a complex with a 1:2 europium/ ligand ratio, obtained from dimethylformamide (dmf ≡ Me2NCHO) solution. This complex is formulated as [ Eu (LH4)(Me2NCHO)6(OH)].LH6.~4Me2NCHO (LH6 = p-t-butyl-calix [6] arene) on the basis of the structure determination. Crystals are monoclinic, P21/n, a 36.11(3), b 23.35(2), c 21.85(2)Ǻ, β 97.46(6)°, Z = 4 formula units; R was 0.11 for 8488 'observed' reflections. The complex is remarkable in that the only interaction of either of the two calixarene ligands (one presumably doubly or triply deprotonated ) with the eight-coordinate europium atom is by way of one behaving as monodentate, the other having no interaction. Eu -O( calix ) is 2.35(1) Ǻ; Eu -O( dmf )6 range from 2.38(2) to 2.49(2)Ǻ, and Eu -O(H ½?) is 2.49(2)Ǻ.

An experimental investigation of the ejected-electron spectra arising from autoionising and Auger transitions in Eu I and Eu II excited by electron impact for the range of incident-electron energies from 20 to 500 eV

The ejected-electron spectra of europium arising from autoionising and Auger transitions in Eu I and Eu II following excitation by electron impact have been measured in the energy region from 0 to 27 eV; incident-electron energies were in the range from 20 to 500 eV. 151 spectral features are tabulated and excitation functions are reported for a number of autoionising and Auger transitions. The chemi-ionisation electron spectrum of europium atoms reacting with oxygen and water vapour is reported in the electron energy region from 0 to 1.5 eV.

Crystal structure and physical properties of EuMo 6S 8 single crystals at ambient pressure

X-Ray analyses were performed at room temperature on single crystals of Eu x Mo 6S 8. Refinement of its crystal structure shows an upper stoichiometry of x = 1.0. Atomic positions and crystallographic data are given in full. Crystals were also characterized through their susceptibility and transport properties. All europium atoms are divalent as confirmed by the magnetization at low temperatures. A welldefined anomaly on the electrical resistivity at T s = 107 K separates the metallic high-temperature rhombohedral phase from the low-temperature nonmetallic (triclinic) phase. Very large residual resistivity ratios obtained for stoichiometric crystals favor our interpretation that the Eu 1.0Mo 6S 8 low-temperature phase must be essentially semiconducting.

Crystal structure and physical properties of EuMo 6S 8 single crystals

X-ray analysis was performed at room temperature on single crystals of Eu x Mo 6S 8. Refinement of its crystal structure shows an upper stoichiometry of x = 1.0. Crystals were also characterized through their susceptibility and transport properties. All europium atoms are divalent as confirmed by the magnetization at low temperatures. A well-defined anomaly on the electrical resistivity at T s = 107 K separates the metallic high -temperture rhombohedral phase from the low-temperature non-metallic (triclinic) phase. Very large residual resistivity ratios obtained for stoichiometric crystals favor our interpretation that the Eu 1.0Mo 6S 8 low-temperature phase must be essentially semiconducting.

An experimental investigation of the ejected-electron spectra arising from autoionising and Auger transitions in Yb I and Yb II excited by electron impact for the range of incident electron energies 8-500 eV

The ejected-electron spectra of europium arising from autoionising and Auger transitions in Eu I and Eu II following excitation by electron impact have been measured in the energy region from 0 to 27 eV; incident-electron energies were in the range from 20 to 500 eV. 151 spectral features are tabulated and excitation functions are reported for a number of autoionising and Auger transitions. The chemi-ionisation electron spectrum of europium atoms reacting with oxygen and water vapour is reported in the electron energy region from 0 to 1.5 eV.

Structural evolution within a series of hydrated bis(dithiooxalato)nickelate(II) of rare earths (RE) 2(H 2O) 2nNi 3(S 2C 2O 2) 6, xH 2O

Single crystals of a series of hydrated bis(dithioxalato) nickelate(II) of rare-earths have been synhesized, namely RE III, Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Er and Yb. The crystal structures were determined by X-ray techniques. The former part of the series (up to Dy) crystallizes in the monoclinic system, space group P2 1|c, while the latter part crystallizes in the triclinic system, space group P 1 . Full-matrix least-squares refinement led to a final reliability factor R = 0.0350 for the europium complex and R = 0.0266 for ytterbium. The characteristic feature of both structures consists of neutral centrosymmeric heteropentanuclear entities (RE) 2(H 2O) 2nNi 3(S 2C 2O 2) 6, which only differ by the number n of water-molecules coordinated to the rare earth: n = 5 for Eu, while n =4 for Yb. The rare earth atom is also bound to four oxygen atoms of two dithiooxalate groups, so the environment of the europium atom can be represented as a tricapped trigonal prism, while only a bicapped trigonal prism is observed for Yb. The conversion between the two structures involves the loss of one water molecule, in the rare earth sphere of coordination, and a concomitant rearrangement of the ligans dithiooxalate on the summits of the coordination polyhedra. In both structures the nickel atoms are coordinated to two dithiooxalate groups via their sulfur atoms. The monoclinic network exhibits channels, running parallel to the direction [1 0 0], in which some water molecules are inserted. The triclinic structure can be described as a pseudo lamellar structure, water molecules being inserted between layers.

The phase diagram of the Eu-Au system

The phase diagram of the Eu-Au system was examined over the whole composition range using differential thermal, X-ray and metallographic analyses. Seven intermediate phases were found: Eu 3 Au (Fe 3 C type), Eu 7 Au 3 (Th 7 Fe 3 type), Eu 3 Au 2 (Er 3 Ni 2 type), EuAu (FeB type), EuAu 2 (CeCu 2 type) and EuAu 5 (CaCu 5 type). The crystal structure of the compound EuAu 4 has not yet been resolved and the stoichiometry was assigned on the basis of differential thermal analysis and micrography data. A limited solid solubility range was found for EuAu 5 whereas all the other compounds appeared to be “line compounds”. Four eutectic points are present in this diagram: 20 at.% Au and 465 °C; 56.5 at.% Au and 900 °C; 75.5 at.% Au and 855 °C; 91.5 at.% Au and 850 °C. No evidence was obtained for a valence change in the europium atoms similar to that found for ytterbium in the analogous Yb-Au system.

A Mössbauer spectroscopic study of the Eu-Hg system

Samples of EuHg x ( x = 1, 2, 3 and 3.6) have been prepared and characterized by chemical analysis and X-ray powder diffractometry. Evidence is presented for narrow ranges of solid solubility and together with other data it is concluded that these substances are better described as being intermetallic rather than metallic alloy in character. The Mössbauer spectroscopic study confirms that the europium exhibits a divalent core in each case. The isomer shift is dependent on the number density of europium atoms in the unit cell. This latter quantity correlates in a similar way with the computed conduction electron density at the europium nucleus. The decrease in electron density at the europium nucleus in these substances compared with that for europium metal is indicative of some degree of normal chemical bonding in these compounds.

Optical Purity Determination and 1H NMR Spectral Simplification with Lanthanide Shift Reagents. II. Thiamylal, 5-Allyl-5-(1-methylbutyl)-2-thiobarbituric Acid

A racemic sample of thiamylal, 5-allyl-5-(1-methylbutyl)-2-thiobarbituric acid, 1, has been shown to exhibit significant enantiomeric shift differences, ΔΔδ, for the CH3- CH proton absorptions when treated with the chiral lanthanide shift reagent, tris[3-(trifluoromethylhydroxy-methylene)- d-camphorato| europium (III), 2, in CDC13 at 28°. For example, at the relatively low molar ratio of 2:1 of 0.181, a value of ΔΔδ of 22 Hz (0.36δ) was observed, which increased to 26 Hz (0.43δ) at a molar ratio of 0.226. These large values, with relatively little lanthanide-induced line-broadening, should make possible the facile determination of optical purity of 1 even with a 60 MHz nmr spectrometer. Parallel studies were run using the achiral shift reagent, tris-(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium (III), 3, to confirm peak assignments. The considerable values of ΔΔδ may reflect the “soft base” character of the sulfur atom in 1. Less effective binding by sulfur to the lanthanide atom could lead to coordination by europium on the carbonyl oxygen, relatively close to the chiral center, providing enhanced AA5 values compared to some related compounds. While several other proton absorptions of 1 appear to show some observable ΔΔδ, they are less valuable for optical purity evaluation because of lower intensity, greater multiplicity, or small ΔΔδ value. The relative slopes of the plots of chemical shift, δ, for runs with 2 or 3, are consistent with the full assignment of the proton absorptions of 1 based on expected proximity of the protons to the complexed europium atom. The observed coupling constants of the vinyl hydrogens of 1 further support the assignments.

Eu 2Re 6S 11, darstellung, kristallstruktur und magnetische eigenschaften

The ternary sulphide Eu 2Re 6S 11 was synthesized by the reaction of Eu 2O 3 with rhenium at 1250 °C in a stream of H 2S. X-ray investigations on a single crystal gave the atomic arrangement. The hexagonal unit cell (a = 902.7(2) pm; c = 3157.4(3) pm; space group, R 3 ̄ c ) contains six formula units. The structure consists of a framework in which [Re 6S 8] clusters are linked in three dimensions according to the formulation {[Re 6S 8]S 6 2 } 4−. The europium atoms are inserted pairwise with a separation of 384.1 pm in holes of this framework. The atomic arrangement is analogous to those of Ba 2Re 6S 11 and Sr 2Re 6S 11, which were previously described with a monoclinic unit cell. Measurements of the magnetic susceptibilities show coupling effects between Eu 2+ ions below 5 K. The determination of the coupling constant J( Eu 2+- Eu 2+) within a pair gave a value of − 0.36 cm −1.

Structure and stereochemistry in 'f-block' complexes of high coordination number. VII. The [M(unidentate X)2(unidentate Y)6] system: Crystal structure of hexaaquadichloroeuropium(III) chloride (a redetermination)

The crystal structure of the title compound [EuCl2(OH2)2]Cl ('europium trichloride hexahydrate') has been redetermined from single-crystal diffractometer data at 295 K and refined to a residual of 0.040 for 1094 independent 'observed' reflections. Crystals are monoclinic, P2/n, a 9.659(3), b 6.529(2), c 7.936(4) �, β 93.67(4)�, Z 2. The europium atom lies on a crystallographic twofold axis, which passes between the two planes of a square-antiprismatic coordination environment in which the two chlorine atoms, on opposite faces, lie cis to each other. Eu-O distances range from 2.401(6) to 2.431(5) �; Eu-Cl is 2.774(2) �.

Site-selective excitation of europium-doped lanthanum oxycarbonates

The excitation at 77 K of the fluorescence of europium in two europiumdoped polymorphs of lanthanum oxycarbonate (LaO)2CO3, type Ia and type II, by UV light yielded several5D0 →7F0 transitions around 5800 A for both compounds. Selective excitation at 77 K of these5D0 levels with a Rhodamine 6G dye laser permitted the identification of La2O3 as a trace impurity in both compounds, and demonstrated the existence in both of two nearly axial sites for the europium atoms. Second-rank crystal field parameters are large (1000 cm−1) for one of the two sites. In the case of type Ia the spectrum is very close to that found for other oxysalts with the quadratic (LnO)nn+ layer such as the oxyhalides.