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Data on classification of spectra and energy levels of atoms of rare earth elements with unfilled 4f-shells have been collected, systematized and analyzed. A brief account is given of methods for determining transition probabilities and lifetimes of the excited states of atoms and ions. Oscillator strengths for spectral lines of Nd(I), Sm(I), Eu(I), Gd(I), Dy(I), Tm(I) and Yb(I) have been measured using Rojdestvensky's hook method. Lifetimes of some of the excited states of Eu(I), Yb(I) and Yb(II) have been determined by using simultaneously the methods of delayed coincidence, hooks, and total absorption. Our results have been compared with those of other investigators. Atoms with unfilled 4f-shells show some regularities.     

Electronic structure of cubic uranium compounds

Self-consistent cellular multiple scattering techniques and photoemission energy distribution curves obtained at 20<hv<80 eV are used to study the density of states of UN and US. The calculations are based on a model using a finite cluster of atoms in a condensed-matter-like boundary potential. The main results refer to the mixing of thes, p, d, andf-states of uranium into a valence and a conduction band. Thef-states form orbitals with the ligands, within the valence and conduction bands. In the nitride the amount off character in the valence band is only 0.3 electrons and thef electrons are in two resonant levels (of each spin) in the conduction band. Only the first of these levels is occupied for the local, alternate from atom to atom, majority spin. In the sulfide the amount off character in the valence band is 0.59 electrons and the rest of thef-levels are in a resonance state (of majority spin) at the beginning of the conduction band. The conduction band is mainly of localized uranium 6d character. The theoretical results compare favorably with the photoemission data reported here.     

The electronic structure and chemical bonding in rare earth chalcogenides according to the Xα SW method—I: EuO,EuS and EuSe

Calculations of the electronic structure for (EuO₆)^10? (EuS₆)^10?, and (EuSe₆)^10? clusters, which represent the nearest-neighbour sphere surrounding Eu in EuO, EuS, EuSe, have been made by the Xα SW method. The contour maps for valence MO's have been drawn. The MO energy diagrams are in reasonable agreement with experimentally derived band structures. In spite of the localized nature of 4f-derived states, there are noticeable admixtures of 4f-states to the valence band. The 5d Eu states hydridize with the chalcogenide valence states, and the covalency of the chemical bonding decreases from EuO to EuSe, which can explain the decrease of elastic modulus, microhardness and chemical stability.     

Excitation and Emission Spectra of Cs2NaLnCl6 Crystals Using Synchrotron Radiation

ABSTRACT

The visible emission and vacuum ultraviolet excitation spectra of the series Cs₂NaLnCl₆ (Ln = Y, Nd, Sm, Eu, Tb, Er, Yb) and Cs₂NaYCl₆:Ln³⁺ (Ln = Sm, Er) have been recorded using synchrotron radiation at room temperature, and in some cases at 10 K. The excitation spectra comprise features associated with charge transfer, excitation from the valence to conduction band, and impurity bands. No d–f emissions were observed for these Ln³⁺ ions, so that the emission bands comprise intraconfigurational 4f ^N –4f ^N transitions and impurity bands, whose natures are discussed. Theoretical simulations of the f–d absorption spectra have been included. The comparison with data from the synchrotron at Desy enables a comprehensive account of the ground (or vibrationally excited ground for Ln²⁺) states of the Ln³⁺ 4f ^N , Ln³⁺ 4f ^N?15d, and Ln²⁺ 4f ^N+1 configurations relative to the valence and conduction bands of Cs₂NaLnCl₆, for which the band gaps are between 6.6 and 8.1 eV.     

On the electronic structure of the light rare earth hydrides

Photoemission (XPS, HeI) and inverse photoemission (hv=9.7 eV) data on Y, La, Ce, Pr and their hydrides are presented. The discussion focusses on the ground state electronic properties of the hydrides and in particular on the empty density of states. In addition the correlation effects which appear in these experimental techniques in the presentce of well localized, partly filled 4f states are stressed. Hybridization is displayed in three typical situations:a) The very existence of a weak 4f-conduction band mixing allows electronic transitions into 4f derived states to be observed by low energy BIS, although the cross section is exceedingly small at this energy-b) 3d core excitation pulls the empty 4f levels close to the hydrogen ligand levels such that they become strongly mixed and the screening level is markedly split-c) A schematic relation is found between core level shifts upon hydriding, charge transfer and the position of the hydrogen induced band, simply by considering the mixing of hydrogen ligand states with metald states.     

Investigation of odd-parity Rydberg states of Eu I with autoionization detection

Isolated-core-excitation (ICE) scheme and autoionization detection are employed to study the bound Rydberg states of europium atom. The high-lying states with odd parity have been measured using the autoionization detection method with three different excitation paths via 4f76s6p[8P5/2], 4f76s6p[8P7/2] and 4f76s6p[8P9/2] intermediate states, respectively. In this paper the spectra of bound Rydberg states of Eu atom are reported, which cover the energy regions from 36000 cm-1 to 38250 cm-1 and from 38900 cm-1 to 39500 cm-1. The study provides the information about level energy, the possible J values and relative line intensity as well as the effective principal quantum number n for these states. This work not only confirms the previous results of many states, but also discovers 11 new Rydberg states of Eu atom.     

First principles study of half-metallic ferromagnetism in Zn1−xEuxS

Density functional theory calculations by using both generalized gradient approximation (GGA) method and the GGA with considering strong correlation effect (GGA+U) for various Eu concentrations x (=0.00, 0.25, 0.50, and 0.75). It is found that after the Europium incorporation, a new localized band appears between the valence and conduction bands, which corresponds to the majority spin of Eu-4f states, the strong correlation effects is very important for the 4f orbit of the Eu atom in ZnEuS. We find that Zn_1−xEu_xS exhibits a half-metallic characteristic, and the ferromagnetic state is more favorable in energy than the antiferromagnetic state. Structural properties are determined from the total energy calculations, and we discuss the electronic structures, total and partial densities of states and local moments.     

Experimental study of145Cs Decay

The decay of mass separated¹⁴⁵Cs (T _1/2= 0.59 s) was studied. Singles gamma and electron spectra were investigated using Ge(Li) and Si(Li) detectors. A level scheme for¹⁴⁵Ba based on the application of energy sum relations is proposed. The β-branching and logft values for the ground and excited states were deduced from the analysis of γ +ce _? intensity balances. Spin and parity assignments based on transition multipolarities are proposed.     

An ab initio study of filled skutterudites ROs4P12 (R = Sm,Eu and Gd)

The elastic, electronic, magnetic and optical properties of filled skutterudite ROs₄P₁₂ (R = Sm, Eu and Gd) have been studied by first principles calculation. The full-potential linearized augmented plane wave method based on density functional theory was employed. For the exchange-correlation potential, local spin density approximation + Coulomb repulsion (LSDA + U) is used to treat the f-electrons more effectively. The numerical values of the elastic parameters are estimated in the framework of the Voigt–Reuss–Hill approximation. OsP-based filled skutterudite with localized 4f and 5d-electrons shows dense energy bands near Fermi energy originating from rare earth and Os atoms. The dense density of states near E_F reveals that these compounds are suitable for thermoelectric application. Optical constants including dielectric function, optical reflectivity and refractive index are calculated for photon energy radiation up to 12 eV. The exchange-splitting of R-4f states were analyzed to explain the ferromagnetic behavior of ROs₄P₁₂.     

On the anomalous susceptibility of small gap magnetic semiconductors (SmS,SmSe, SmTe)

The magnetic susceptibility of the Sm chalcogenides shows a large dependence on the nature of the anion. In the three compounds (which under pressure become metallic) the energy needed to promote an electron from the 4f shell to the conduction band is very small. We present here a mechanism based on the hybridization between f states and band states that relates the anomalies of the susceptibility with the energy gaps.