Electron-stimulated desorption of europium atoms from an oxidized tungsten surface

The yield of europium atoms in electron-stimulated desorption from Eu layers adsorbed on the surface of oxidized tungsten was studied with a surface-ionization detector as a function of the incident-electron energy, surface coverage by europium, and degree of tungsten oxidation. The yield of Eu atoms measured as a function of electron energy exhibits a distinct resonant character with peaks at electron energies corresponding to europium and tungsten core-level ionization energies. The peaks associated with the europium ionization reach a maximum intensity at europium coverages less than 0.1 and decrease subsequently to zero with increasing coverage, while the peaks due to tungsten ionization pass through the maximum intensity at a monolayer europium coverage. The coverage corresponding to the maximum europium atom yield grows with increasing tungsten oxidation. The results obtained are accounted for by the formation of the europium and tungsten core excitons. In the first case, the particles desorb in the reverse motion toward the surface of the oxidized tungsten; in the second, they desorb as a result of repulsion between the tungsten core exciton and the EuO molecule.     

Electron-stimulated desorption of europium atoms from the surface of oxidized tungsten

An analysis of the yield q of europium atoms is made, and scenarios of electron-stimulated desorption are put forward. Expressions are obtained for the dependence of q on the coverage of oxidized tungsten by europium atoms.     

XAFS at Eu-L3 edge and UV-VUV excited luminescence of europium doped strontium borophosphate prepared in air

The local structure and the valences of europium in SrBPO₅:Eu prepared in air were checked by means of XAFS at Eu-L₃ 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 4f⁶5d-4f⁷ transition of Eu²⁺ 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 Sr²⁺ and Eu³⁺ 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.     

On the interaction of an electron with a nonspherical atom

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.     

Isotope separation of some rare-earth elements by two step photoionization

The experimental results of the laser isotope separation (LIS) of europium, samarium and gadolinium atoms by two step selective photoionization are reported. The atom vapour of Eu, Sm, Gd atoms has been produced by the heating of a crucible containing the metal. A dye laser has been used as a selective exciter of the atoms. For the photoionization N₂-laser or mercury lamp have been used.     

Electron-stimulated desorption of europium atoms from the surface of oxidized tungsten: Concentration dependence of the low-energy peak

The nature of electron-stimulated desorption of europium atoms Eu⁰ at low incident electron energies E _e (～30 eV) and the specific features of the dependence of the yield of europium atoms Eu⁰ on their concentration on the surface of oxidized tungsten are discussed. The crucial stage is found to be the primary event of vacancy creation in the inner 5p shell of the europium adatom. As follows from estimates, only the first of the two possible ionization scenarios (intratomic electron transfer to the outer shell of the Eu adatom or ejection of the knocked-out electron into vacuum) results in Eu⁰ desorption. The concentration threshold of the Eu⁰ yield is determined.     

The magnetic and hyperfine properties of iron in silicon carbide

The magnetic and hyperfine properties of iron impurities in 3C- and 6H- silicon-carbide are calculated using the abinitio method of full-potential linear-augmented-plane-waves. The iron atoms are introduced at substitutional carbon, Fe _C , and silicon, Fe _Si , sites as well as at the tetrahedral interstitial sites with four nearest neighbours carbon atoms, Fe _I (C), and four nearest neighbours silicon atoms, Fe _I (Si). The effect of introducing vacancies at the neighbours of these sites is also studied. Fe atoms with complete neighbors substituted at Si or C sites are found to be nonmagnetic, while Fe atoms at interstitial sites are magnetic. Introduction of a vacancy at a neighboring site reverse the picture.     

Mössbauer study of the substituent effect in mixed ligand complexes of europium (III)

A series of europium (III) mixed ligand complexes containing phenanthroline, benzoic acid and their derivatives, respectively, as ligands, were investigated by Mössbauer spectroscopy. The substituents changed the electron density on the donor atoms of the ligands by their electrophilic or nucleophilic nature and changed the stereochemistry of the coordination sphere by their different space requirement. Both effects were reflected in the isomer shift values. The basicity changes on the donor atoms due to the substituents were characterized by the Hammett 6 values of latters. The correlation betweenEu isomer shifts and the Hammett 6 values of the corresponding substituents on the ligands of otherwise analogous europium (III) compounds indicated the binding mode in the complexes /1/.     

邻苯二甲酸—邻菲罗啉—铕—铽络合体系的荧光性能研究

波长为３６５ｎｍ的紫外光激发下均可发出特征荧光的邻苯二甲酸－邻菲罗啉－铕和铽固体络合物以机械研磨和化学作用两种方式进行混合，研究了这两系列混合络合物的荧光光谱和红外光谱。结果表明，由于铕、铽之间存在相互影响，其荧光强度变化较大，而荧光发射峰位基本不变。经化学混合后铽对铕的荧光强度有极强的敏化作用，铕对铽具有很强的猝灭作用，并用红外光谱对上述四种络合物体系的结构进行了表征     

Effect of chlorine on the flame spectra of rare-earth elements

The effect of CHCl₃ vapor on rare-earth metal vapors in an acetylene-air flame has been studied spectroscopically. It has been established that both the molecular spectra of the oxide molecules and the emission spectra of the atoms (Eu, Yb) are weakened in the presence of this vapor. In the case of europium and lutecium, the spectra contain new (chloride molecule) bands. Investigation of the relationship between the emission intensities of the atoms or molecules and the partial pressure of chlorine in the flame suggests that molecules of the MeCl₂ type are formed in the flame.     

Formation of thin luminescent Eu3+-LB films by in situ coordination with 2,3,5,6-tetra(2′-pyridyl)pyrazine and 1-octadecanol in pure and mixed Langmuir monolayers

The in situ complexation between 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) molecules and europium ions at the air–liquid interface by means of mixed 1-octadecanol Langmuir films is reported. These films were transferred to solid supports by means of the Langmuir–Blodgett (LB) technique. The EDS maps attested the homogeneity of the LB films as well as the presence of the europium ions. The mixed alcohol/tppz LB film contained a larger amount of europium ions as compared to the pure octadecanol LB film. This work reports the production of a thin luminescent Eu³⁺ film containing europium ions using only alcohol molecules as ligands—an unexpected result, since it is well known that there is an occurrence of non-radiative deactivation of excited europium by hydroxyl groups. Europium ion multiple binding sites were detected from lifetime decay measurements of these films in the presence of tppz molecules.     

二甲亚砜硝酸铕的晶体结构

二甲亚砜硝酸铕Eu(NO₃)₃·4DMSO晶体属单斜晶系。空间群为C_2/c-C⁶_2h。晶胞参数a=14.806(9)?,b=10.948(3)?,c=15.335(4)?,β=108.07(7)°晶胞内分子数z=4。用PW-1100四圆衍射仪收集强度数据,独立衍射点数为2270个。用重原子法解晶体结构。结构参数用全矩阵及方块矩阵最小二乘法修正,最后R因子为0.069。铕离子由10个氧原子配位。铕和配位氧之间的距离:Eu—O_DMSO=2.38?,Eu—O_(NO3)=2.61?。 关键词：     

Adsorption stage in the formation of Eu-Si(111) thin-film structures

The adsorption stage in the formation of the Eu-Si(111) interface has been studied within a broad temperature range by thermal and isothermal desorption spectroscopy, low-energy-electron diffraction, Auger electron spectroscopy, and the contact potential difference method. It is shown that the ordering of an adsorbed europium film is accompanied by silicon surface reconstruction throughout the coverage range studied, 0<θ≤1.8. This self-organized process is also shown to be thermally activated. Ordered adsorbed europium layers have been found to be made up of 2D islands, whose structure depends on the amount of the metal deposited on the surface. The energy required to remove atoms from an island to vacuum has been determined. This energy decreases with decreasing 2D lattice constant of the islands. This pattern of its variation is accounted for, in the final count, by the decrease of the number of the Si surface atoms not bound directly to Eu atoms.     

Nuclear magnetism and the trivalent europium ion

Enhanced nuclear moments occur in atoms, molecules and all the transition groups of the periodic table. They are unusually large for lanthanide ions, with electrons of the 4f group, but the mechanism responsible for enhancement for other ions produces “anti-shielding” effects for the trivalent europium ion. These greatly reduce the effective nuclear magnetic moments in the ground state J=0. Here it is suggested that dynamic nuclear polarization can be used to increase the effective nuclear moments, and off-set the anti-shielding. The substance is europium vanadate, “doped” with a small percentage of samarium ions.     

Occurence and correlation of two non-equivalent sites for europium in EuPd3B

Mössbauer spectroscopy has been used to investigate the mechanism which affects the valence state of europium in EuPd₃B. The obtained results are interpreted in terms of a correlation between two non equivalent sites each in a fluctuating valence state.     

Elastic scattering of electrons by europium and ytterbium atoms

The method of relativistic optical potential is applied to studying elastic scattering of electrons by europium and ytterbium atoms in a wide range of collision energies up to 2 keV. The angular dependences of the scattering differential cross sections and the energy dependences of the scattering integral (total, elastic, momentum transfer, and viscosity) cross sections are calculated in both spin-polarized and spin-unpolarized approximations. It is shown that the spin-polarized approximation should be used to calculate the scattering cross sections at energies below 10 eV for a europium atom. The low-energy scattering of an electron by a europium atom is characterized by P-, D-, and F-wave shape resonances. For an ytterbium atom, the calculated cross sections are in good agreement with available experimental data and with those obtained by calculation in terms of the relativistic convergent close-coupling method.     

MMgF_4：Eu（M＝Ca，Sr，Ba）体系中铕离子的发光中心及价态

合成了铕离子激活的ＭＭｇＦ４．磷光体，研究了Ｅｕ３＋离子的光谱特征与基质化合物的关系，存在三类发光中心，讨论了基质组成对铕离子价态的影响。     

Europium adsorption on a tungsten surface with various degrees of oxidation

The kinetics of europium adsorption on a W(100) face with various degrees of oxidation were studied by thermal desorption and Auger electron spectroscopy. The spectrum of Eu atoms desorbed thermally from the W(100) face consists of three successively filling desorption phases whose desorption activation energy decreases from 3 to 2.1 eV with an increase in the surface coverage. The thermodesorption spectrum of Eu atoms from the W(100) face coated with a monatomic oxygen film contains five successively forming desorption phases, with the desorption activation energy increasing to 4 eV for the high-temperature phase. The oxidized W is reduced by europium, and the desorption of the W oxides is replaced by that of EuO. After a monolayer film has formed, the Eu film adsorbed on tungsten starts to grow in the form of three-dimensional crystallites. As the degree of W oxidation increases, the Eu film becomes less nonuniform, until a solid Eu film starts to grow on bulk W oxides and completely screens the tungsten Auger signal.     

聚乙烯吡咯烷酮与苯磺酸铕相互作用研究

用变温红外光谱法和荧光光谱法研究了聚乙烯吡咯烷酮与苯磺酸铕的相互作用。聚乙烯吡咯烷酮的酰胺基团可与苯磺酸铕中的铕离子发生络合配位作用,导致聚乙烯吡咯烷酮的酰胺Ⅰ带发生红移。这种络合配位作用,使原本不溶于氯仿的苯磺酸铕可溶于含聚乙烯吡咯烷酮的氯仿溶液。在苯磺酸铕固体的发射光谱中,只能观察到铕离子的f—f跃迁特征发射峰,而在苯磺酸铕浓水溶液的荧光光谱中,亦可观测到苯磺酸根的π*→π跃迁峰,说明苯磺酸铕在水溶液中存在解络合现象。苯磺酸铕在溶液中的解络合行为使铕离子周围的可配位空间增大,这为PVP的酰胺基团与铕离子发生络合配位作用创造了条件。     

Spectroscopic Determination of Heparin Sodium Using Europium (III) as a Probe Ion

Abstract

A sensitive, rapid, accurate and precise procedure for the microdetermination of heparin sodium in bulk, in injection and in blood serum. The procedure was built around the fact that heparin possesses many active binding sites; carboxylic, hydroxylic, amino and sulphonated groups, which are strongly bound to Eu³⁺ ions. Such binding enhances the europium emission at 616 nm which is a forbidden transition. The emission of europium at 592 nm comes from a non hypersensitive transition and is not affected by the ligand which is bound to europium ions. The intensity ratio R, defined as I₅₉₂/I₆₁₆ was used to determine the amount of free and bound europium ions. There is a linear relationship between bound europium ions and heparin sodium within the concentration range 1–12 ug. mL^?1 (0.07–0.84 USP. IN). Reaction conditions were studied and percentage recoveries was 99.77 ± 1.68. The relative stability of the complex was 1.2E⁵ and the correlation coefficient was 0.99923. Heparin was isolated from serum using ECTEOLA-cellulose and Sephadex G25 columns. The method shows good agreement with an anilinonaphthalene-1-sulfonate (ANS) and protamine fluorometric method.