Density of states and the problem of Sm valence

Density of states for Sm metal has been calculated in DFT/GGA approximation using the same treatment for f and s-d bands. It is concluded that the 4f electrons of Sm must be considered as valence electrons, not shallow core states. Therefore the 4f-5d transition cannot change the valence of Sm, which may be characterized (if necessary) by the sum of all electrons in the s-d-f valence bands. The possibility of alternative interpretation of UPS spectra of Sm adsorbed films is illustrated by calculations of DOS (density of states) for oxygen-contaminated Sm crystal.     

The YbNi interface studied with photoemission spectroscopy

The development of the ytterbium valence band region was followed with Synchrotron radiation induced Photoemission Spectroscopy (SPS) by interdiffusion of Yb into a Ni (110) single crystal in order to identify the valence conditions of Yb in the bulk and on the surface. During this process, also the width of the Ni L₃VV Auger transition was investigated with X-ray induced Photoemission Spectroscopy (XPS), reflecting the electron donation of Yb to the Ni valence band. By comparison between theory and experiment, strong multiplet splittings were found to take place in the 4d and 5p core level spectra of Yb due to the promotion of one 4f electron to the valence band by reaction with Ni. The 5p level is demonstrated to resonate strongly at hν=181 as a consequence of the 4d–4f giant resonance.     

Valence variations in the monolayer regime of Sm on the Nb(110) surface

Sm overlayers in the monolayer regime, deposited on a Nb(110) single-crystal surface at room temperature, have been studied by means of high-resolution photoelectron spectroscopy of the Nb 3d_5/2 core level and the Sm valence band. In the submonolayer regime, the Sm valence varies from mainly divalent for very low coverages to essentially trivalent close to a complete monolayer. Above 1 ML, a new divalent component appears in the Sm 4f spectra, corresonding to divalent Sm in the second layer. The mixed valence in this overlayer system is concluded to be heterogeneous (all Sm atoms have integer but site-dependent valence). Sm forms ordered overlayers on Nb(110) and the Sm growth is consistent with a layer-by-layer growth mode (Frank–van der Merwe growth).     

The unoccupied electronic structure characterization of hydrothermally grown ThO2 single crystals

Single crystals of thorium dioxide ThO₂, grown by the hydrothermal growth technique, have been investigated by ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES), and L₃, M₃, M₄, and M₅ X‐ray absorption near edge spectroscopy (XANES). The experimental band gap for large single crystals has been determined to be 6 eV to 7 eV, from UPS and IPES, in line with expectations. The combined UPS and IPES, place the Fermi level near the conduction band minimum, making these crystals n‐type, with extensive band tailing, suggesting an optical gap in the region of 4.8 eV for excitations from occupied to unoccupied edge states. Hybridization between the Th 6d/5f bands with O 2p is strongly implicated. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical analysis of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy

We studied the chemical state of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy (XPS), which were fabricated using dual-target magnetron sputtering by controlling the power applied to both metal and chalcogenide targets. On the basis of the valence band spectra obtained, it was suggested that semiconducting SmS has the final state corresponding to the Sm²⁺(4f⁶) configuration below the Fermi level, and metallic SmS has mainly the Sm³⁺(4f⁵) final state and a virtual band state in the Sm 5d band, contributing to the delocalization of 4f electrons and the emergence of metallic conductivity (4f⁶d⁰-4f⁵d¹). Thus, the spectra of our fabricated SmS thin films correspond to the band structure obtained from the dielectric property. This is the first work performed on the intrinsically prepared metallic SmS while the former works done for the sample transformed from semiconductor to metal phase by hard polishing.     

Electronic structure and magnetic properties of YbCuAl

The electronic band structure of YbCuAl has been calculated using the self-consistent full potential nonorthogonal local orbital minimum basis scheme based on the density functional theory. We investigated the electronic structure with the spin–orbit interaction and on-site Coulomb potential for the Yb-derived 4f orbitals to obtain the correct ground state of YbCuAl. The exchange interaction between local f electrons and conduction electrons play an important role in the heavy fermion characters of them. The fully relativistic band structure scheme shows that spin–orbit coupling splits the 4f states into two manifolds, the 4f_7/2 and the 4f_5/2 multiplet.     

Electronic structure and magnetism of YbRhSn

The electronic band structure of YbRhSn has been calculated using the self-consistent full potential nonorthogonal local orbital minimum basis scheme based on the density functional theory. We investigated the electronic structure with the spin-orbit interaction and on-site Coulomb potential for the Yb-derived 4f orbitals to obtain the correct ground state of YbRhSn. The exchange interaction between local f electrons and conduction electrons play an important role in the heavy fermion characters of them. The fully relativistic band structure scheme shows that spin-orbit coupling splits the 4f states into two manifolds, the 4f_7/2 and the 4f_5/2 multiplet.     

Comparison of light rare earths N4,5-level soft X-ray and auger electron appearance-potential spectra

Appearance-potential Spectroscopy (APS) probes the binding energy of core levels and local conduction band states of atoms in the surface region. Soft X-ray APS (SXAPS) and Auger electron APS (AEAPS), respectively, measure the differential X-ray fluorescence and secondary electron yields as a function of incident electron energy. We have obtained the N_4,5-level SXAPS and AEAPS spectra of La, Ce, Pr, Nd and Sm metals. Both spectra exhibit multiplet structure below the expected 4d excitation threshold and a broad, 10–20 eV wide peak above the threshold followed by small peaks of decreasing intensity. The data are used to gain an understanding of the decay mechanism following the excitation of the core levels in these spectroscopies. The strong similarity observed between the SXAPS and AEAPS indicates that the characteristic emission and not the bremsstrahlung dominates the spectral lineshape in APS.     

BaFClxBr1－x:Sm2+中5D2→7F0跃迁几率及其对烧孔效率的影响

本文以BaFClxBr1－x:Sm2+中5D2→7F0的跃迁几率随x变化为中心对BaFClxBr1－x:Sm2+体系4f5d带的激发光谱、5D2→7F0跃迁的荧光衰减随温度的变化特性、5D2→7F0的跃迁几率等进行了研究。从而得出结论:在BaFClxBr1－x:Sm2+中,随Br含量的增大,4f5d带与5D2能级更加接近,使7F0→5D2的吸收截面增大,从而可能提高在5D2:能级烧孔的效率。     

MeBeF4(Me=Ca,Sr,Ba)中钐的价态及光谱

讨论了MeBeF4基质中钐离子的光谱及价态.还原气氛中仅在SrBeF4和BaBeF4中观察到了Sm2+的发射.     

SryBa1－yFCl0.5Br0.5:Sm2+在光谱

本文对无机光谱烧孔系列材料SryBa1－yFCl0.5Br0.5:Sm2+中不同组份的样品(y=0,0.25.0.5,0.75.1.00)4f5d能带的激发光谱、不同温度下5D2、5D1、5D0→7F0跃迁的荧光衰减进行了测量,研究了组份的变化对4f5d能带的位置,5D2、5D1、5D0→7F0跃迁的几率和烧孔效率的影响,并得出结论:在该系列材料中,随组份y的增加,4f5d带与5DJ能级更加接近,5D0→7F0的电子跃迁几率增大,烧孔效率提高。     

Optical spectra and crystal-field analyses of samarium in the centrosymmetric hexakis(antipyrine)samarium(III) tri-iodide and tri-perchlorate systems

Optical absorption and emission measurements are reported for single crystals of Sm(AP)₆I₃ and Sm(AP)₆(ClO₄)₃ (where AP denotes an antipyrine ligand molecule). Crystal-field energy levels split out of the 4f ⁵ electronic configuration of Sm³⁺ are located and assigned from the locations and polarizations of magnetic-dipole origin (no-phonon) lines observed in the optical spectra. The energy levels are analyzed in terms of a parametric hamiltonian that assumes D _3d crystal-field symmetry at the Sm³⁺ sites. Crystal-field interaction parameters obtained from calculated-versus-experimental energy level fits are reported and compared for the Sm(AP)₆I₃ and Sm(AP)₆(ClO₄)₃ systems. Good data fits are obtained for both systems, and the rank-two and rank-four crystalfield parameters are reasonably well-determined by these fits. The rank-six parameters are less well-determined. The values determined for the rank-four crystal-field parameters are essentially identical for the tri-iodide and triperchlorate systems; however, the magnitude of the rank-two parameter for Sm(AP)₆I₃ is twice that for Sm(AP)₆(ClO₄)₃. Magnetic-dipole line strengths are calculated for absorptive transitions originating from crystal-field levels of the ⁶H_5/2 (ground) multiplet and for emissive transitions originating from the ⁴G_5/2 (excited) multiplet.     

LED用荧光粉Sr（S1-xSex）：Eu^2＋的合成和光谱性质研究

采用高温固相法合成了Sr(S1-xSex)系列硫属化合物掺Eu2 荧光粉.XRD表明荧光粉的组成为单相,而且体系Sr(Sl-xSex):0.005Eu2 中晶胞参数随着组成的变化呈现良好的线性关系,遵守韦加定律.漫反射光谱与激发光谱吻合,说明荧光粉吸收的能量能够有效地激发发光中心而发光,激发光谱中较低能量区域覆盖了400～500 nm的光谱范围,与蓝光LED芯片的发射光匹配.发射光谱呈现的是Eu2 离子的5d→4f特征跃迁发射带,当x由0增加到1.0的过程中,发射峰值波长由617 nm逐渐蓝移到571 nm.不同基质中掺杂的Eu2 离子的荧光寿命均为微秒数量级,与Eu2 离子的4f65d1→4f7跃迁相符合.将荧光粉封装在发蓝色光(λ=460 nm)的GaN芯片上制作了LED器件,测量了器件的发光强度、色纯度和色坐标等参数.Sr(S1-xSex):Eu2 系列硫属化合物掺铕荧光粉能够有效地被GaN芯片发出的蓝色光激发,发出从橙色到红色的可见光,是一类较好的LED用荧光粉.     

钡钇氟化物中Eu2+离子的激发光谱和发射光谱

在298和77K下分别研究BaYF5(BaF2·YF3)中Eu2+的激发和发射光谱。Eu2+的发射光谱中,除了一个属5d-4f跃迁的宽发射带外,还有一组6PJ→8S7/2的4f-4f跃迁窄谱线发射。它们的发射强度与Eu2+的浓度和温度有关。由於Eu2+从4f7基态跃迁到4f65d1态产生两个宽的激发带,4f65d(eg)和4f65d(t2g)。实验证实,Eu2+的6PJ→8S7/2的窄谱线发射主要来自高能级的t2g激发能弛豫的结果。     

Collision parameters of N2-broadened methane lines in R5 multiplet of 2ν3 band. Multispectrum fitting of overlapping spectral lines

The results of the investigation of absorption spectra of the methane R5 multiplet of 2ν ₃ band, broadened by nitrogen, are presented. The absorption spectra of the methane-nitrogen mixture (CH₄:N₂ = 1:113.36) were recorded, using a two-channel photometric spectrometer, based on a tunable diode laser. The multispectrum least-squares fitting procedure was applied to all experimental spectra, recorded at different pressures, using the program, developed at IAO SB RAS (Protasevich, 2011). The program is based on a relatively simple line-profile model proposed in Pine (J. Quant. Spectrosc. Radiat. Transf. 57:145, 1997) and linear pressure dependence of the line-profile parameters. The line center positions, intensities, broadening, shifting, and mixing coefficients were determined for four lines of the methane R5 multiplet. The results have been compared with other available data.     

Manganese silicide single crystal and films deposited on Si(1 1 1): A comparative spectroscopic study

A comparative experimental study is presented of the electronic properties of MnSi films grown on Si(1 1 1) and of MnSi single crystals, using X-ray absorption spectroscopy (XAS), and core level and valence band photoemission spectroscopy (PES). No significant differences in the electronic structure of the two systems can be found.Absorption measurements on the Mn 2p threshold show a mixed valence ground state, where the multiplet structure is washed out by the hybridisation of the Mn 3d states with the Si sp states. These results are also confirmed by photoemission (PE) spectra from the valence band and the Mn 3s, 3p and 2p core levels.Strong attention has been paid to the effect of contamination. The occurrence of multiplet effects in the absorption spectra indicates unambiguously the localisation of the Mn 3d electrons in Mn-O bonds, which strongly influences the electronic properties of these systems.     

Metal (Cu; Pd) adsorption on MgO: investigations with MIES and UPS

MgO films (2-nm thick) were grown on W(110) while metastable impact electron (MIES) and photoelectron (UPS(HeI)) spectra were collected in situ; apart from the valence-band emission no additional spectral features could be detected. The oxide surface was exposed to metal atoms (Cu; Pd) (substrate at 300 K). For Cu, but not for Pd/MgO, a characteristic initial decrease of the surface work function by about 0.4 eV is observed for small exposures. Metal-induced intensity develops above the top of the O2p valence band in UPS caused by 3dCu (4dPd) emission. The emission seen for Cu/MgO in the MIES spectra above the 2pO valence band is attributed to the ionization of Cu4s states of neutrally adsorbed Cu species; the shape of the MIES spectra suggests island growth even at the lowest studied exposures. For Cu/MgO the critical coverage for the transition from 2D to 3D island growth, as determined with MIES, is estimated as 0.15 monolayers. PACS 79.20; 79.60.Dp; 73.22.-f; 82.80.Pv     

The interaction of oxygen with gadolinium: UPS and XPS studies

The interaction of oxygen with evaporated Gd films at 300 K has been studied for the first time using AlK α XPS and Hel and Hell UPS. The characteristic changes in the Gd(6s5d) and O(2p) valence bands, Gd(4f), Gd(5p) and Gd(4d) core levels, and O(2s) and O(1s) core levels were studied. Evidence is presented for the initial formation of an intermediate oxidation state at low exposure (characterized by a new Gd valence band with a maximum in the DOS at ～ 2.5 ev below E_F and an ～ 0.6 eV shift in Gd(4f)) prior to formation of Gd₂O₃ where the Gd(6s5d) valence band disappears completely, as expected for Gd³⁺. In the higher exposure range there is little further increase in the oxide thickness, which is estimated as $\text{? 20}\text{A}\text{?}$, but there is a slow replacement of O by OH, as characterized by a second O(1s) feature at 532.3 eV and OH 1π and 3σ orbitals in UPS at ～ 6.7 and 11.5 eV. The interpretations are supported by parallel studies on bulk Gd₂O₃ and by Ar⁺ sputtering experiments. Comparisons are made to other rare earth oxidation studies.     

Resonant photoemission and Ta 5p core reflectance spectra of 1T- and 2H-TaSe2

Reflectance spectra of 2H- and 1T-TaSe₂ have been measured at room temperature in the region between 20 and 60 eV. The multiplet structures in the Ta 5p core excitation region are analyzed on the localized excitation model. The ultraviolet photoemission spectra have revealed a resonant enhancement of the Ta 5d and Se 4p valence bands for the excitation of the Ta 5p core states. The difference of the multiplet structures as well as of the resonant behavior between 1T- and 2H-polytypes has elucidated the hybridization of the Se 4p states with the Ta 5d states in the valence bands of TaSe₂.     

Theory of core-level spectroscopy of rare-earth oxides

A review is presented of the recent development in theoretical studies of X-ray photoemission spectra (XPS) and X-ray absorption spectra (XAS) for rare-earth sesquioxides (R₂O₃) and rare-earth dioxides (RO₂). From the analysis of 3d XPS for R₂O₃ (R = La, Ce,..., Yb) and RO₂ (R = Ce, Pr, Tb) with the impurity Anderson model (without the multiplet coupling effect), we estimate the strength of the covalency hybridization between rare-earth 4f and oxygen 2p states, the charge transfer energy and other physical quantities, and discuss their systematic variation with the change in rare-earth elements. Two possible mechanisms for the splitting of the 3d XPS are pointed out for R₂O₃. One is the initial-state hybridization for R = La, Ce, Pr and Nd; the other is the final-state hybridization for R = Eu and Yb. For RO₂ (R = Ce, Pr, Tb), both of the initial- and final-state hybridizations are essential in explaining the 3d XPS spectra. Then, we study the effect of the intraatomic multiplet coupling on 3d and 4d XPS for La₂O₃, Ce₂O₃, Pr₂O₃, Nd₂O₃, Yb₂O₃ and CeO₂. The multiplet coupling effect is not very important for the 3d XPS, causing only an additional spectral broadening and some minor spectral structures. In the analysis of 4d XPS, however, the interplay between the multiplet coupling and the hybridization plays an essential role. Finally, we study the multiplet structure in 3d and 4d XAS for CeO₂ and PrO₂. It is shown that the original atomic multiplet structure in these XAS is strongly modified by the interatomic hybridization effect, and the experimental multiplet structure is explained consistently with the analysis of 3d and 4d XPS, by the mixed-valence ground state with strong covalency hybridization.