Europium Atoms Research Articles

Photoelectron spectroscopy of europium-silicon cluster anions, EuSin− (3⩽n⩽17)

We report the photoelectron spectra of EuSi(n) (-) cluster anions (3<or=n<or=17). They reveal dramatic electronic rearrangements over the size range n=10-12. In particular, a marked increase in the adiabatic electron affinity of EuSi(12) (2.8 eV) compared to its stoichiometric neighbor, EuSi(11) (1.9 eV), is observed. We propose that a significant geometric reorganization due to the encapsulation of a europium atom occurs in this size range and is responsible for the detected changes in the electronic structure. In light of this interpretation, EuSi(12) is the smallest fully endohedral europium-silicon cluster.

Crystal and molecular structure and luminescence properties of the europium trifluoroacetate complex with dipyridyl

The crystal structure of [Eu(Dipy)(TFA)3(H2O)3] · Dipy (where TFA− is the trifluoroacetate anion and Dipy is, 2,2′-dipyridyl) has been studied by X-ray diffraction. The coordination polyhedron of the europium atom is a distorted square antiprism [EuO6N2] with the nonplanar quadrilateral faces. The coordinated and non-coordinated dipyridyl molecules are linked pairwise through π stacking interactions into an infinite pile with an overlap of up to 50% of the molecular surface areas. An increase in the luminescence intensity of the compound upon its UV irradiation is explained.

Synthesis of europium(III) complex with phthalocyanine and 8-hydroxyquinoline

Phthalocyanine metal complexes are classed with the best organic semiconductors [1]. Their use in molecular optoelectronics is determined by the possibility for combining various physicochemical and photovoltaic properties. We have synthesized previously unknown europium(III) complex with phthalocyanine and hydroxyquinoline ligands. We anticipated that a combination in a single molecule of a phthalocyanine ring possessing hole conductivity with emitting properties of europium atom and electrontransfer ability of hydroxyquinoline fragment will endow the complex with polyfunctionality so that it could used as material for organic light-emitting diodes.

Parameters of luminescence and the local structure of Eu3+ centers in fluorogermanate glasses

The influence of the chemical nature of the local environment of Eu3+ ions on the parameters of luminescence of these centers in glasses of the (BaGeO3)1 − x − y(Al2O3)x(0.45CaF2 · 0.55MgF2)y (x = 0.25, y = 0; x = 0.17, y = 0.17; x = 0.15, y = 0.22; x = 0.07, y = 37.00; x = 0, y = 0.45) system is investigated. The oxidation state of europium atoms and the degree of homogeneity of their local environment in the glasses are determined using 151Eu Mossbauer spectroscopy.

Highly luminescent water-soluble lanthanide nanoparticles through surface coating sensitization

Water-soluble La0.95Eu0.05F3·AEP (AEP = aminoethylphosphate) nanoparticles (NPs) were shown to react with 6-carboxy-5′-methyl-2,2′-bipyridine (bipyCOO−) in water, resulting in an increase of more than two orders of magnitude of the europium centred emission upon excitation at 305 nm. Nanoparticles coated by the bipyCOO− ligands were prepared by surface ligand exchange in water, isolated and characterized by infrared spectroscopy, transmission electron microscopy, energy dispersion X-ray analysis and dynamic light scattering. These analyses compared to those of the genuine NPs sample confirmed the partial replacement of AEP by bipyCOO−, with retention of the original morphology of the particles. The photo-physical properties of the isolated La0.95Eu0.05F3·bipyCOO− NPs were measured in water by absorption, steady-state and time-resolved luminescence spectroscopies and revealed that the large increase of the luminescence of the NPs is due to a surface generated antenna effect where coated bipyCOO− moieties efficiently absorb light and transfer the energy to the emitting europium atoms of the NPs.

Superfluorescence from europium atom at 629.977 nm

Visible superfluorescence at 629.977nm is observed in europium atom with very high optical conversion efficiency on the transition 5d6p 10F7/2→5d6s 10D7/2. The peak intensity of fluorescence varies as square of the number of atoms in the excited state (N), which shows the superfluorescence character of the transition. The ratio of average superfluorescence power to excitation laser power is observed to be ∼15% in the forward direction.

Europium(II) in glasses of the Al2O3-SiO2-MnO-Eu2O3 system

Triply and doubly charged states of europium are revealed by 151Eu Mossbauer spectroscopy in the structure of glasses of the composition (mol %) 19.5Al2O3, 31.5SiO2, 26.5MnO, and 22.5Eu2O3. The isomer shifts in the Mossbauer spectra of Eu3+ and Eu2+ ions in the structure of glasses differ from the isomer shifts in the spectra of the Eu2O3 and EuO compounds. This difference is explained by the fact that the electron density at 151Eu nuclei is affected by the manganese and aluminum atoms, which are not bound directly to the europium atoms. The broadening of the spectra of the Eu2+ ions in glasses is caused by the nonuniform isomer shift.

Ferromagnetic Semiconducting EuO Nanorods

Nanorods of EuO, a concentrated magnetic semiconductor, are synthesized. SQUID magnetometry shows a large ferromagnetic response for the nanorods of 6.9 μB per europium atom. Magnetic circular dichroism verifies that the nanowires are indeed ferromagnetic and semiconducting.

Odd-parityJ=11∕2autoionizing Rydberg series of europium below the5dD49threshold: Spectroscopy and multichannel quantum-defect-theory analysis

The odd-parity $J=11∕2$ autoionizing states of europium atom below the $5d$ $^{9}D_{4}$ threshold are investigated by a two-step laser photoionization scheme via the $4{f}^{7}5d6p$ $^{10}F_{9∕2}$ intermediate state. The observed resonances are classified into two autoionizing Rydberg series (with $n=15$ to 55) converging to the $5d$ $^{9}D_{4}$ limit and eight members ($n=13$ to 20) of two autoionizing Rydberg series converging to the higher $5d$ $^{9}D_{5}$ limit. The single series converging to the $5d$ $^{9}D_{3}$ limit is not efficiently excited. The observed four Rydberg series are assigned in $jj$ coupling as $5dnd$ $(4,j)$ and $5dnd$ $(5,j)$ with $j=3∕2$ and $5∕2$. Apart from the $5dnd$ $(5,5∕2)$ series, the majority of autoionizing resonances exhibits narrow linewidths and quasisymmetric line shapes, reflecting this way the weak coupling between the discrete levels and the adjacent continua. The experimental data are analyzed through the semiempirical phase-shifted multichannel quantum defect theory. The theoretically calculated energy level positions and excitation profiles are in good agreement with the experimental ones, thus confirming the identification of the observed structures. The constructed Lu-Fano plot and computed admixture coefficients reveal weak and localized interactions among the Rydberg series members.

Low-temperature complexes of europium atoms and dimers with cyanophenylpyridines and alkylcyanophenylpyridines

It is shown by IR-Fourier and UV-visible spectroscopy that two biligand complexes of different stoichiometric composition Ln·2L and 2Ln·2L (Ln = Eu; L = 4-pentyl-4′-cyanophenylpyridine) are formed in the course of low-temperature co-condensation of metal and ligand vapors on the surfaces cooled with liquid nitrogen. Quantum-chemical modeling of the equilibrium structures of the mono-and binuclear complexes of europium with unsubstituted cyanophenylpyridyl and para-ethylcyanophenylpyridyl ligands was carried out. The main geometrical parameters of these compounds were determined. For mononuclear complexes, there is a competition between two mechanisms of coordination of the metal atom: formation of sandwich π complexes by interactions with the π orbitals of the aromatic ligand system and σ coordination at the nitrogen atoms of the pyridine ring. The sandwich structures of the binuclear complexes with 4-ethylcyanophenylpyridine are stabilized by N…H intermolecular contacts between the N atom of the cyano group and the terminal H atom of the ethyl group. The spectral shifts and the relative thermal stability of complexes with varying nuclearity are discussed.

Synthesis, structure and properties of SrAu 3In 3 and EuAu 3In 3—New indides with gold zig-zag chains

New indides SrAu 3In 3 and EuAu 3In 3 were synthesized by induction melting of the elements in sealed tantalum tubes. Both indides were characterized by X-ray diffraction on powders and single crystals. They crystallize with a new orthorhombic structure type: Pmmn, Z=2, a=455.26(9), b=775.9(2), c=904.9(2) pm, wR2=0.0425, 485 F 2 values for SrAu 3In 3 and a=454.2(2), b=768.1(6), c=907.3(6) pm, wR2=0.0495, 551 F 2 values for EuAu 3In 3 with 26 variables for each refinement. The gold and indium atoms build up three-dimensional [Au 3In 3] polyanionic networks, which leave distorted hexagonal channels for the strontium and europium atoms. Within the networks one observes Au2 atoms without Au–Au contacts and gold zig-zag chains (279 pm Au1–Au1 in EuAu 3In 3). The Au–In and In–In distances in EuAu 3In 3 range from 270 to 290 and from 305 to 355 pm. The europium atoms within the distorted hexagonal channels have coordination number 14 (8 Au+6 In). EuAu 3In 3 shows Curie–Weiss behavior above 50 K with an experimental magnetic moment of 8.1(1) μB/Eu atom. 151Eu Mössbauer spectra show a single signal at δ=−11.31(1) mm/s, compatible with divalent europium. No magnetic ordering was detected down to 3 K.

Hydrothermal synthesis, crystal structure and properties of 2-D and 3-D lanthanide sulfates

Two new lanthanum sulfates DySO 4(OH) 1 and Eu 2(SO 4) 3(H 2O) 8 2 have been hydrothermally synthesized. The colorless crystals were characterized by IR, TGA, ICP and XRD. The structure was determined by single-crystal X-ray diffraction. 1 crystallizes with monoclinic symmetry, space group P2(1)/ n [ a=7.995(4) Å, b=10.945(5) Å, c=8.164(4) Å, α=90°, β=93.619(6)°, γ=90°, V=713.0(5) Å 3, Z=8]. It displays a three-dimensional framework, based on the novel Dy–O chains connected by the sulfate groups through helical chains. 2 crystallizes with monoclinic symmetry, space group C2/ c, [ a=13.5605(17) Å, b=6.7676(8) Å, c=18.318(2) Å, α=90°, β=102.265(2)°, γ=90°, V=1642.7 (4) Å 3, Z=4]. Its layered framework is attained by the europium atoms connected by the sulfate groups arranged in a helical manner.

Novel rare earth quinolinolate complexes

The reaction of europium 8-quinolinolate Eu(OQ) 3 with calcium 8-quinolinolate, Ca(OQ) 2 , in the flux 1,2,4,5-tetramethylbenzene (TMB) at 210 °C yields the bimetallic [Eu 2 Ca(OQ) 8 ], which is a linear tri-nuclear complex with two eight coordinate europium atoms flanking a six coordinate calcium atom bonded by six bridging phenolate oxygen atoms. A similar reaction between La(OQ) 3 and Co(OQ) 2 gave [LaCo 2 (OQ) 7 ], in which two six coordinate cobalt atoms flank an eight coordinate lanthanum atom with six bridging phenolate oxygen atoms and a terminal OQ group.

Synthesis and structural characterization of lanthanide coordination polymers constructed from a 13-membered macrocycle

The lanthanide coordination polymers bearing a 13-membered macrocycle, [(13-EDTA-pnOH)H2] were synthesized. The products [Ln(13-EDTA-pnOH)(H2O)2·NO3]n (Ln = Eu(1), Tb(2), Dy(3)) have been obtained by MS, IR and element analyses. The solid-state structure of 1 was established by single-crystal X-ray analysis. The coordination geometry around the central metal atom in complex 1 is a nine-coordinated, tricapped-trigonal prism having six donor atoms (two amine nitrogen atoms, two amide oxygen atoms and two carboxymethyl oxygen atoms) from one ligand, one oxygen atom from a neighboring ligand, and two more oxygen atoms from two water molecules. The europium atoms are linked by-Eu-O-C-O-Eu-bridges to form an infinite chain.

Structure, Magnetic Properties and 151Eu, 119Sn Mössbauer Spectroscopy of Eu5Sn3S12 and Eu4LuSn3S12

Eu5Sn3S12 and Eu4LuSn3S12 were synthesized and their structures refined from single crystal data (Pmc21, Eu5Sn3S12: a = 3.908(1), b = 20.115(4), c = 11.451(2) Å ; wR2 = 0.0519 for 3048 F2 and 122 parameters; Eu4LuSn3S12: a = 3.920(1), b = 20.132(4), c = 11.459(2) Å ; wR2 = 0.0737 for 3298 F2 and 122 parameters). The structures contain one-dimensional chains of edge-sharing SnS2S4/2 octahedra and corner-sharing SnS3S2/2 trigonal bipyramids, running parallel to [100]. Five europium sites are seven- or eightfold coordinated by sulfur atoms. Lutetium atoms in Eu4LuSn3S12 show a strong site preference for one of the two Eu3+ positions of Eu5Sn3S12 and no structural disorder was observed. Both compounds show static mixed valence according to Eu2+ 3 Eu3+ 2 Sn4+ 3 S2− 12 and Eu2+ 3 Eu3+Lu3+Sn4+ 3 S2− 12 , which was confirmed by temperature dependent magnetic susceptibility measurements. The experimental magnetic moments of 14.6(1) (Eu5Sn3S12) and 14.1(1) (Eu4LuSn3S12) μB/f.u. indicate that each of the two sulfides contains three divalent europium atoms per formula unit. Magnetic ordering for Eu5Sn3S12 and Eu4LuSn3S12 sets in below 5 and 3 K, respectively. Both sulfides show metamagnetic or spin-flip transitions in the magnetization curves at 3 K (2 K) with full saturation of the europium magnetic moments at 3 K (2 K) and 80 kOe. 151Eu Mössbauer spectra fully confirm the Eu2+ and Eu3+ site occupancies. At 4.2 K an increase in line width indicates small hyperfine fields at the europium nuclei.

Synthesis, Crystal Structure, and Luminescent Properties of Novel Eu3+ Heterocyclic β-Diketonate Complexes with Bidentate Nitrogen Donors

New tris(heterocyclic beta-diketonato)europium(III) complexes of the general formula Eu(PBI)3.L [where HPBI = 3-phenyl-4-benzoyl-5-isoxazolone and L = H2O, 2,2'-bipyridine (bpy), 4,4'-dimethoxy-2,2'-bipyridine (dmbpy), 1,10-phenanthroline (phen), or 4,7-diphenyl-1,10-phenanthroline (bath)] were synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), 1H NMR, high-resolution mass spectrometry, thermogravimetric analysis, and photoluminescence (PL) spectroscopy. Single-crystal X-ray structures have been determined for the complexes Eu(PBI)3.H2O.EtOH and Eu(PBI)3.phen. The complex Eu(PBI)3.H2O.EtOH is mononuclear, and the central Eu3+ ion is coordinated by eight oxygen atoms to form a bicapped trigonal prism coordination polyhedron. Six oxygens are from the three bidentate HPBI ligands, one is from a water molecule, and another is from an ethanol molecule. On the other hand, the crystal structure of Eu(PBI)3.phen reveals a distorted square antiprismatic geometry around the europium atom. The room-temperature PL spectra of the europium(III) complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the multiplet (7F0-4). The results demonstrate that the substitution of solvent molecules by bidentate nitrogen ligands in Eu(PBI)3.H2O.EtOH richly enhances the quantum yield and lifetime values. To elucidate the energy transfer process of the europium complexes, the energy levels of the relevant electronic states have been estimated. Judd-Ofelt intensity parameters (Omega2 and Omega4) were determined from the emission spectra for Eu3+ ion based on the 5D0 --> 7F2 and 5D0 --> 7F4 electronic transitions, respectively, and the 5D0 --> 7F1 magnetic dipole allowed transition was taken as the reference. The high values obtained for the 4f-4f intensity parameter Omega2 for europium complexes suggest that the dynamic coupling mechanism is quite operative in these compounds.

Synthesis, Structure Refinement and Thermal Behavior of HEuP2O7×4H2O.

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Direct Experimental Evidence for Atomic Tunneling of Europium in CrystallineEu8Ga16Ge30

Mössbauer-effect and microwave absorption experimental evidence unambiguously demonstrates the presence of slow, approximately 450 MHz, tunneling of magnetic europium between four equivalent sites in Eu8Ga16Ge30, a stoichiometric clathrate. Remarkably, six of the eight europium atoms, or 11% of the constituents in this solid, tunnel between these four sites separated by 0.55 A. The off centering of the atoms or ions in crystalline clathrates appears to be a promising route for producing Rabi oscillators in solid-state materials.

Multichannel quantum-defect-theory analysis of the observed odd-parity5dndautoionization Rydberg series of neutral europium

The spectra of autoionizing Rydberg series of europium atoms are analyzed by a semiempirical multichannel quantum defect theory (MQDT). Experimental data were obtained using two-step resonance ionization spectroscopy below the 5d {sup 9}D{sub J} ionic multiplet. The MQDT model involving five channels and three limits is used to analyze the observed four odd-parity Rydberg series. Theoretical energies are computed and compared with the experimental values. The Rydberg series are assigned on the basis of calculated admixture coefficients. The series having J=3/2 are interpreted as 5dnd (2,3/2), 5dnd (2,5/2), 5dnd (3,3/2), and 5dnd (3,5/2). Interseries perturbations and perturbations due to levels of configuration 5dnd (4,5/2) are investigated. Some of the unobserved levels are also predicted.

Synthesis and Characterization of the First Dinuclear Europium (II) Complex Supported by Carbon-Bridged Biphenolate Ligand

Anhydrous EuCl 3 reacted with sodium carbon-bridged biphenolate LNa 2[L = 2,2′-methylene bis(6-tert-butyl-4-methyl-phenoxo] in a 1:1 molar ratio in THF in the presence of HMPA (HMPA = hexamethylphosphoric triamide), then the product formed in situ was reduced by Na-K alloy to generate the divalent carbon-bridged biphenolate europium complex [LEu(HMPA) 2] 2(THF) 4(1) in a good isolated yield. Complex 1 was fully characterized by elemental analysis, NMR and IR spectra, and X-ray structural determination. The crystal data of complex 1 are monoclinic, P2 1/ c space group, a = 1.6521(3) nm, b = 2.8274(3) nm, c = 1.2074(2) nm, β = 111.723(6)°, V = 5.2393(14) nm 3, Z = 2, D c = 1.259 mg·m −3, μ = 1.304 mm −1, F(000) = 2092, R = 0.0815, wR = 0.1723. Complex 1 is a dimer with two Eu - 0 bridges. The coordination geometry of each europium atom can be best described as a distorted trigonal bipyramid.