Spectrum analysis of U-doped LaBr3 single crystals. Part 1: crystal-field analysis

Single crystals of U³⁺:LaBr₃ were grown by the Bridgman-Stockbarger technique. High-resolution polarized absorption spectra of the crystals were recorded at 4.2 K in the 4000-50,000 cm⁻¹ range. Sixty-four experimental crystal-field energy levels of the U³⁺ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators with an r.m.s. deviation of 28 cm⁻¹. The performed analysis of the spectra enabled the determination of crystal-field parameters and assignment of the observed 5f³→5f³ transitions. The effects of selected CCF operators on the splitting of some specific U³⁺ multiplets have been investigated and the obtained values of Hamiltonian parameters are discussed and compared with those reported in previous analyses.     

Spectroscopic studies on the mixed Nd3+-La3+ and Ho3+-Gd3+ acetate systems as an example of the determination of stability constants from electronic spectroscopic data

The previously worked out spectroscopic method of determination of stability constants of lanthanide ions displaying hypersensitive transitions in absorption spectra [ions of f²–f⁶ and f⁸–f¹² configurations] has been extended to all the lanthanide ions. The method is based upon measurements of the oscillator strength of hypersensitive transitions of mixed systems of equimolar concentrations containing two different lanthanide ions, in the spectrum one of which a hypersensitive transition is easily observed. The method was proved on the La³⁺-acetate and Gd³⁺-acetate systems, both the lanthanide ions having no hypersensitive transitions within the generally available UV and VIS measurement range.     

Application of the oscillator strength of “hypersensitive” transitions to the investigation of complex equilibria of lanthanide ions—I: Method of the evaluation of stability constants

A method of evaluation of stability constants for the lanthanide complexes from the changes of oscillator strengths of “hypersensitive” f-f transitions as a function of total ligand concentration is proposed. The method is discussed for neodymium acetate and glycolate and holmium lactate complexes. Stability constants calculated for mononuclear species are compared with the potentiometric data of Sonesson. This method is also useful for the calculation of thermodynamic parameters using measurements of the dependence of the oscillator strength on temperature.The method is limited to lanthanide ions with f²-f⁶ and f⁸-f¹² electronic configurations.     

Application of Multi-step Excitation Schemes for Detection of Actinides and Lanthanides in Solutions by Luminescence/Chemiluminescence Laser Spectroscopy

The use of laser radiation with tunable wavelength allows the selective excitation of actinide/lanthanide species with subsequent registration of luminescence/chemiluminescence for their detection. This work is devoted to applications of the time-resolved laser-induced luminescence spectroscopy and time-resolved laser-induced chemiluminescence spectroscopy for the detection of lanthanides and actinides. Results of the experiments on U, Eu, and Sm detection by TRLIF method in blood plasma and urine are presented. Data on luminol chemiluminescence in solutions containing Sm(III), U(IV), and Pu(IV) are analyzed. It is shown that appropriate selectivity of lanthanide/actinide detection can be reached when chemiluminescence is initiated by transitions within 4f- or 5f-electron shell of lanthanide/actinide ions corresponding to the visible spectral range. In this case chemiluminescence of chemiluminogen (luminol) arises when the ion of f element is excited by multi-quantum absorption of visible light. The multi-photon scheme of chemiluminescence excitation makes chemiluminescence not only a highly sensitive but also a highly selective tool for the detection of lanthanide/actinide species in solutions.     

Dynamic effect on the structure of X-ray photoelectron spectra of lanthanide fluorides and oxides

Dynamic effect on the fine structure of X-ray photoelectron spectra of lanthanide oxides and fluorides is discussed. The Ln4p electron spectra are considerably complicated by the interaction between the configurations of themain one-hole and additional two-hole final states of 4p⁵4d⁵⁴fⁿ ↔ 4p⁶4d⁸fⁿ⁺¹ type. The effect of the nature of atoms in the nearest environment of lanthanide ions on the fine structure parameters is evaluated. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1059–1066, November–December, 1998.     

Studies of electronic configurations in the emission spectra of lanthanides and actinides: application to the interpretation of Es I and Es II, predictions for Fm I

The interpretation of the spectra of free atoms and gaseous ions in the 4f^N and 5f^N periods became less active after critical compilations of energy levels appeared. However, several spectra are still under study and the application of the Racah-Slater and HFR methods to extended sets of configurations leads to revisions and additions. In doubly charged ions of lanthanides, the treatment of configuration interaction by means of effective parameters and by extension of the basis of states are both important. Concerning actinides, calculations of several observables (Landé factors and isotope shifts in Pu I, hyperfine constants, transition probabilities) prove the quality of eigenfunctions. The classification of Es I and Es II has been extended and radial parameters for fine and hyperfine structures have been derived. Level predictions for the next element fermium are supported by parameter extrapolations.     

Electronic structure of free and doped actinides: N and Z dependences of energy levels and electronic structure parameters

Theoretical study of electronic structure of antinide ions and its dependence on N and Z are presented in this paper. The main 5f^N and excited 5f^Nn′l′^N′ configurations of actinides have been studied using Hartree-Fock-Pauli approximation. Results of calculations of radial integrals and the energy of X-ray lines for all 5f ions with electronic state AC⁺¹−AC⁺⁴ show approximate dependence on N and Z. A square of N and cubic of Z are ewalized for the primary electronic parameters of the actinides. Theoretical values of radial integrals for free actinides and for ions in a cluster AC⁺ⁿ:[L]_k are compared, too.     

System analysis of the thermodynamic properties of binary lanthanide hydrides

Systems analysis of available data on the thermodynamic properties of binary lanthanide hydrides is carried out. The standard thermodynamic characteristics of lanthanide dihydrides (Δ_f H ^o, S ^o, C _p ^o ) and their hypothetical trihydrides (Δ_f H ^o) are calculated. The calculations are performed using a semiempirical method that takes into account the effects of the number of f-shell electrons and the spin and orbital angular moments of ground states of the lanthanide ions on the thermodynamic properties of the compounds studied. It is established that the thermodynamic characteristics of the hydrides exhibit an antibatic behavior with respect to the atomic numbers of the natural series lanthanides. The tetrad effect was revealed for these series of compounds.     

Thermodynamics of thiocyanate complexes of trivalent actinides and lanthanides

The thermodynamic parameters ΔF, ΔH and ΔS of the complexes of Cm(III), C(III) and Tm(III) with the SCN^? ion have been determined at 30°C in ammonium ion medium of unit ionic strength by the temperature variation method. It has been concluded that both the thiocyanate complexes of trivalent actinides and lanthanides are predominantly inner-sphere type. The higher stability of the second complexes of trivalent actinides is reflected either in the enthalpy or the entropy change depending on the degree of hydration of the trivalent actinide ions. The implications of the greater free energy change for PuSCN²⁺ as compared with other trivalent actinide or lanthanide first thiocyanate complexes are discussed.     

4fN-15d组态自旋允许与禁戒跃迁能级的研究

通过稀土光谱理论，计算了三价稀土离子的4f^N-15d组态能级的f与d电子间的库仑相互作用，结果表明对于重稀土元素，其自旋允许跃迁能级位置高于自旋禁戒跃迁能级位置，并且两种能级间的能级差随f电子数的增加而依次减小。对于轻稀土元素,则自旋禁戒跃迁能级位置高于自旋允许跃迁能级位置。结果很好地解释了自旋禁戒跃迁能级的光谱现象。     

Thermodynamic properties of 5f elements

The function P(M) defined by Nugent, Burnett and Morss (J. Chem. Therm.5, 665 (1973)) has been reexamined utilizing new experimental data. This function now appears to be linear with Z for the actinide series. New values for ΔH°_S and ΔH°_f for each element of the actinide series are derived. The entropy of formation ΔS°_f of the M_aq³⁺ ions was estimated which allowed the determination of the free energy change ΔG° and redox potential E° for the couple M_aq³⁺/M. The redox potentials for E°(M(X)/M) for all known redox states of the actinide series were estimated.     

First-Principles Calculations of Magnetism in Nanoscale Carbon Materials Confining Metal with <Emphasis Type="Italic">f</Emphasis> Valence Electrons

The f electrons in the unfilled shell of actinide and lanthanide display complex bonding behavior and the hybridized sp electrons in carbon could show spin polarization in finite nanostructures. Correspondingly, materials combining these two features exhibit abundant magnetic properties. In this paper, we outline our first-principles calculations on various nanoscale carbon materials confining U and Gd which are representative actinide and lanthanide, respectively. The complex interaction between f electrons and sp electrons make the induced magnetic property sensitive to metal specie and carbon confinement. Specially, (1) The magnetism could be suppressed by stronger adsorption with vacancy sites on graphene and adjusted by varying the valence state of some endohedral metallofullerenes (EMFs). (2) The magnetic coupling between metal and carbon structures could be promoted by large curvature when confinement site is carbon nanotubes and altered by the adatom defect on fullerene cages. (3) Untrivial magnetic property with large net spin and asymmetric spin distribution is obtained by confining U atom and Gd atom in one fullerene as a heteronuclear EMF. These results contribute to a systematic understanding of the magnetism in nanoscale carbon materials confining metal with f valence electrons.     

Crystal-field analysis of low-temperature UCl3 and UBr3 absorption spectra

High-resolution absorption spectra of thin films of UCl₃ and UBr₃ have been measured at 4.2 K in the 4000–30 000 cm⁻¹ range. The determined crystal-field lines were used in a computational analysis employing free-ion operators, one-electron crystal-field operators as well as two-particle correlation crystal-field operators. The performed analysis enabled the determination of the Hamiltonian parameters and an unambiguous assignment of 57 and 46 crystal-field levels with a mean error of 31 cm⁻¹ for UCl₃ and UBr_3, respectively.     

Investigations of the ionic self-diffusion coefficients of the trivalent lanthanide 152Eu(III) in diluted Eu(ClO4)3 solutions in 1,4-dioxane + water mixtures at 298.15 K

The measurement of ionic self-diffusion coefficient D of the trivalent lanthanide ion ¹⁵²Eu(III) in asymmetrical electrolytes of Eu(ClO₄)₃ in hydro-organic water–dioxane mixtures (at a low dielectric constant) at 298.15?K, by the open-end capillary method gives evidence of the progressive association of ion pairs. The study of the different physicochemical properties in all the domains of composition shows the existence of three distinct behaviours. The application of association theory to such an asymmetrical electrolyte (3?:?1) with a polyvalent cation enables us to delimit the validity of the Bjerrum and Fuoss's association theories. Since there is similarity of the coordination chemistry of trivalent lanthanide and actinide ions, this study comes within the framework of previous works of the investigation of structure properties of the f-elements in solution carried out in some previous papers.     

Lanthanide thermodynamic predictions

For the plus-two and plus-three lanthanide ions, ΔH_f is inversely related to the sums of the ionic radii by ΔH°_f = Q_n + A/(r_Ln³⁺+ r_xn?) + B. This equation reproduces the known values for the plus-three oxides and the halides, and predicts the absolute hydration energies of the aqueous lanthanide(III) ions. The model is also used to calculate ΔH_f of the lanthanide(II) oxides and fluorides. Based upon the enthalpies of disproportionation, EuO, YbO, SmF₂, EuF₂ and YbF₂ are predicted to be stable.     

Transition energies of Rn- and Fr-like actinide ions by relativistic intermediate Hamiltonian Fock-space coupled-cluster methods

The extrapolated intermediate Hamiltonian (XIH) Fock-space coupled cluster method in the 1-hole 1-particle sector is applied to calculate excitation energies of Xe-like La³⁺ and the Rn-like actinides Ac³⁺, Th⁴⁺, Pa⁵⁺ and U⁶⁺. Large basis sets and model spaces are used, the latter made possible by the XIH scheme. Comparison with experiment for the La ion shows very good agreement, with a mean absolute error of 0.11 eV for 14 excitations in the largest basis (37s33p25d23f14g12h11i6k), lending credence to predicted energies for the actinide ions. Significant Breit term contributions appear, and the DCB Hamiltonian is therefore used. Excellent results are obtained in the one-particle sector, where more experimental values are available. The MAE for 17 transition energies of La²⁺ is below 0.01 eV, and 18 levels of the Fr-like actinide ions Ac²⁺, Th³⁺ and U⁵⁺ give a MAE of 0.06 eV. Second-order perturbation theory values differ considerably from all-order and experimental energies.     

Theoretical crystal-field parameters for the YOCl:Eu3+ system. A simple overlap model

Some theoretical aspects of a simple overlap model in lanthanide crystal-field theory are discussed. The model is applied to the YOCl:Eu³⁺ system and satisfactory results are obtained.     

Shape-persistent macrocycles: efficient extraction towards lanthanide and actinide elements

The extraction of three shape-persistent aromatic oligoamide macrocycles (cycloaramides) bearing either apolar or polar side chains at the periphery of the rings has been investigated towards some representative lanthanide and actinide ions, and alkali metal ions. The results from the liquid–liquid extraction of lanthanide and thorium ions from aqueous solutions into dichloromethane revealed remarkably high extractability of up to 99% and selectivity over alkali metal cations. The stoichiometry of the complex formed between the macrocycle and Eu³⁺ or Th⁴⁺ was determined to be 1:1.     

Distribution of lanthanide and actinide elements between bis-(2-ethylhexyl)phosphoric acid and buffered lactate solutions containing selected complexants

With the renewed interest in the closure of the nuclear fuel cycle, the TALSPEAK process is being considered for the separation of Am and Cm from the lanthanide fission products in a next generation reprocessing plant. However, an efficient separation requires tight control of the pH which likely will be difficult to achieve on a large scale. To address this issue, we measured the distribution of lanthanide and actinide elements between aqueous and organic phases in the presence of complexants which were potentially less sensitive to pH control than the diethylenetriaminepentaacetic (DTPA) used in the process. To perform the extractions, a rapid and accurate method was developed for measuring distribution coefficients based on the preparation of lanthanide tracers in the Savannah River National Laboratory neutron activation analysis facility. The complexants tested included aceto-, benzo-, and salicylhydroxamic acids, N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), and ammonium thiocyanate (NH₄SCN). The hydroxamic acids were the least effective of the complexants tested. The separation factors for TPEN and NH₄SCN were higher, especially for the heaviest lanthanides in the series; however, no conditions were identified which resulted in separations factors which consistently approached those measured for the use of DTPA.     

A structural study of ternary lanthanide orthoscandate perovskites

Ternary lanthanide scandates (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Ho) have been synthesized at ambient pressure. Their structure has been investigated at room temperature by Rietveld analysis of powder X-ray diffraction data. The Ln-scandates are orthorhombic perovskites, adopting space group Pbnm (? 62), a≈b≈√2a_p, c≈2a_p, Z=4. Heavy lanthanides (Er-Lu), and Y do not form perovskites at ambient conditions. Compositionally driven phase transitions were not observed. The unit-cell parameters decrease with increasing ScO₆ octahedron rotation and atomic number of the Ln cation. In common with lanthanide orthoferrites, the uniform structural evolution is interrupted at the middle-heavy part of the lanthanide sequence. This is probably due to an interplay between: (i) enlargement of the ScO₆ octahedra relative to BO₆ in other perovskites (e.g., FeO₆ in GdFeO₃); (ii) reduction in size of the first coordination sphere of Ln³⁺ coincident with the lanthanide contraction; (iii) coincident expansion of the second coordination sphere due to screening effects of O^I1 on O^I2, and entry of Sc to the lanthanide coordination sphere; (iv) complex mixing between oxygen and lanthanide lanthanide f- and scandium d-orbitals. In the series studied, Ln³⁺ are in eight-fold coordination (tetragonal antiprism), and are considerably displaced from the center of the LnO₈ polyhedron along [001]. Evolution of the crystallochemical characteristics through the Ln orthoscandate series is complex due to both the antipathetic distortions of A- and B-site coordination polyhedra and interaction of the orbitals of oxygen, Ln and Sc. Empirically obtained limits of Goldschmidt and observed ^viiit_o tolerance factors for ternary LnBO₃ compounds adopting the Pbnm structure are 0.795 and 0.841, respectively.