硫化锰电子结构的软X射线共振非弹性散射研究

利用软X射线共振非弹性散射谱(resonant inelastic soft X-ray scattering, RIXS)对3d过渡金属硫化物中的硫化锰(MnS)电子结构进行了研究.通过分析Mn²⁺的2p⁶3d⁵→2p⁵3d⁶→2p⁶3d⁵二次光子过程，得到了共振非弹性散射谱中的两类非弹性峰，d-d电子跃迁和电荷转移(charge-transfer)跃迁.这两部分跃迁分别共振增强于L边附近及伴随峰附近.基于Hartree-Fock方法的多重态计算分别模拟了原子近似下和立方体O_h对称群下共振非弹性散射谱及吸收谱.计算得MnS实际晶体场10Dq值介于0.80eV—0.85eV之间.对MnS和MnO CT跃迁差异的讨论表明MnS较强的CT跃迁来源于其较窄的能隙宽度. 关键词： 软X射线共振非弹性散射 软X射线吸收谱 d-d跃迁 电荷转移     

Resonant inelastic x‐ray scattering from highly correlated dysprosium compounds

Dy₂O₃ and Dy metal's resonant inelastic x‐ray scattering (RIXS) spectra were measured in the Beijing Synchrotron Radiation Facility. As a bulk sensitive probe and two‐photon process, RIXS provides more information on the electronic structure of matter. In this full RIXS experiment, the 2p⁶4fⁿ→ 2p⁵4fⁿ5d¹ (2p⁵4f^{n + 1}5d⁰) → 2p⁶3d⁹4fⁿ5d¹ (2p⁶3d⁹4f^{n + 1}5d⁰) channel of two samples (Dy₂O₃ and Dy metal) was studied. Further comparison shows that there are many differences in the RIXS spectra. Dy metal has only a single resonance and its 5d band is broader than that of Dy₂O₃. In the resonant regime, it has a lower final state energy, whereas in the non‐resonant regime it exceeds Dy₂O₃. This causes a broader bandwidth of the main final state B and a narrower bandwidth in the resonant and non‐resonant regime. The pre‐edge structure in Dy L₃ absorption spectra was also resolved using RIXS, which cannot be seen in conventional XAS owing to 2p core hole lifetime broadening. Copyright © 2005 John Wiley & Sons, Ltd.     

AC-conductivity and Raman spectra of polyiodide inclusion compounds (β-cyclodextrin)2·KI7·16H2O and (β-cyclodextrin)2·LiI7·14H2O during the dehydration process

The frequency and temperature dependence of ac-conductivity and phase shift of polycrystalline inclusion compounds (β-CD)₂·KI₇·16H₂O and (β-CD)₂·LiI₇·14H₂O (β-CD=β-cyclodextrin) has been investigated over the frequency and temperature ranges of 0-100 kHz and 240-420 K. A Raman spectroscopic study and calorimetric measurements are also accomplished. The Arrhenius exponential behaviour of the ac-conductivity for T>275 K is caused by the contribution of the metal cations K⁺, Li⁺. This contribution is facilitated by the water-net via the Grotthuss mechanism. The ac conductivity starts deviating from the exponential behaviour with lower increasing rate, at 347 K for β-K and at 353 K for β-Li reaching a maximum value at 371.1 and 361.8 K, respectively, and then decreases rapidly due to the gradual removal of all the water molecules. The values 371.1 and 361.8 K are characterized as semiconductor to metal transition temperatures. The shift of the initial Raman peak at 179 cm⁻¹ to the final value 165 cm⁻¹ as the temperature increases reveals the lengthening of I₂ units via a charge transfer interaction in I⁻₇ units. A second topical maximum value of conductivity appears at 399.7 K for β-K and 403 K for β-Li, attributed to the sublimation of I₂.     

Preparation,characterization, magnetic property,and Mössbauer spectra of the β-FeOOH nanoparticles modified by nonionic surfactant

β-FeOOH nanoparticles have been prepared in a microemulsion system with nonionic surfactant polyoxyethylene(4)nonylphenylether CH₃(CH₂)₈C₆H₄O(CH₂OCH₂)₄H. The powder X-ray diffraction, infrared spectra, and transmission electron microscopic images indicate that the products are 20–30 nm length nanorods with a crystal structure belonging to monoclinic β-FeOOH and lattice parameters of a=0.9981, b=0.2948, c=1.0485 nm and β=92.26°. The size and shapes of β-FeOOH nanoparticles can be manipulated by the surfactant. The modified β-FeOOH nanoparticles are paramagnetic at room temperature and may be antiferromagnetic or weakly ferrimagnetic at lower temperatures. The ⁵⁷Fe Mössbauer spectra show that the magnetic structure transforms below 150 K and two kinds of Fe–O octahedra exist in the lattice of the modified β-FeOOH nanoparticles. The numbers of each kind of Fe–O octahedra are not the same at room temperature or at low temperatures.     

Magnetic properties of MnO nanocrystals dispersed in a silica matrix

Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol% MnO doped silica gel and glasses studied in the temperature range 10-290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hyperfine (HF) lines. Additionally five spin-forbidden doublets have been observed at 100 K and below. Small spreads in spin Hamiltonian parameters (D and E) imply that the ligand field environments of Mn(II) ions embedded in the silica glass are nearly uniform. Monotonous decrease in HF linewidth in going from 120 °C gel to 800 °C calcined glass has been interpreted as the continuous decrease in population of isolated Mn²⁺ ions in silica glass matrix resulting in the decrease of magnetic dipolar interactions leading to the observed decrease in HF linewidth. XRD and TEM of sample calcined at 1000 °C shows the presence of nanocrystals of MnO having orthorhombic crystalline phase and sizes about 10 nm. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of MnO nanocrystals in the 5-300 K temperature interval have demonstrated that the MnO nanocrystals display superparamagnetic-ferromagnetic transition at low temperatures. X-band EPR linewidth data plotted versus inverse of temperature (1/T) for samples calcined at 900 and 1000 °C (EPR recorded in the vicinity of 0.35 T applied field) depict similar transitions.     

Reflectivity measurements of superionic conductors for Li ion secondary battery materials

The reflection measurements of superionic conductors LiCoO₂ and Li_1-xCoO₂, which are already in use for the positive electrode material of 4 V rechargeable lithium batteries, have been performed in the millimeter wave region from 6 to 60 cm⁻¹ using the electron storage ring facilities of Institute of Molecular Science in Okazaki. The increase of the reflectivity has been observed in the low wavenumber region below 10 cm^-1 above 300 K in Li_1-xCoO₂ for the first time, while the reflectivity of LiCoO₂ has almost the constant value in all observed temperature region between 77 to 380 K. The results will be discussed in connection with our previous results of LiNiO₂.     

Temperature dependence of the absorption spectrum of CH4 by high resolution spectroscopy at 81 K: (II) The icosad region (1.49-1.30 μm)

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by differential absorption spectroscopy between 6717 and 7351 cm⁻¹ (1.49-1.36 μm) using a cryogenic cell and a series of distributed feed back (DFB) diode lasers. The investigated spectral region corresponds to the very congested low energy part of the icosad for which the HITRAN database provides neither rovibrational assignments nor the lower state energies. The positions and strengths at 81 K of 9389 transitions were obtained from the spectrum analysis. The minimum value of the measured line intensities (at 81 K) is on the order of 10⁻²⁶ cm/molecule. From the variation of the line strength between 81 K and 296 K, the low energy values of a total of 4646 transitions were determined. They represent 79.4% and 68.4% of the total absorbance in the region at 81 and 296 K, respectively, and include 28 transitions assigned to the ν₂+4ν₄ band near 6765 cm⁻¹. The reliability of the method based on the association of lines with coinciding centers in the 81 K and 296 K spectra is discussed. The results of the present analysis have been combined with previously analyzed high energy part of the icosad dominated by the ν₂+2ν₃ band near 7510 cm⁻¹. The line list for the whole icosad (6717-7655 cm⁻¹) consists of 12 865 transitions at 81 K.     

X-ray absorption near edge structure (XANES) for KCl

The cluster calculations of K and L_2,3 edge XANES of K and Cl in KCl within the multiple scattering theory formalism using nonlocal HF potentials with abd without consideration of core hole field were performed. For K spectra the influence of the core hole potential is rather weak and the results are similar to those obtained with Xα potentials. For L_2,3 spectra, particularly for that of K⁺, core hole field leads to a radical redistribution of oscillator strength caused mainly by the spatial rearrangement of d like states. Calculated XANES curves show good over-all agreement with the experimental spectra (the L_2,3 absorption of K⁺ in KCl was measured using the synchrotron radiation of the USSR Academy of Sciences storage ring VEPP-2M in Novosibirsk).     

Optical spectroscopy of heavily Ho-doped BaY2F8 crystals

The ultraviolet, visible, and near IR (0.8-2.4 μm) luminescence spectra of BaY₂F₈ single crystals heavily doped with Ho³⁺ ions (10 and 30 mol%) have been investigated at room temperature and 12 K, together with the luminescence decay curves (up to 300 μs) of the visible emission. Excitation in the visible region gives rise to very strong emission bands originating from the first ⁵I₇ level and located around 2070 nm. However the ⁵I₇ emission is not observed upon excitation at wavelengths shorter than 300 nm. The inter-ionic processes are found to shorten the decay times of the levels emitting in the visible region with respect to the corresponding radiative lifetimes.     

Oxidation state characterization in Cr oxides by means of Cr-Kβ emission spectroscopy

High-resolution Kβ spectra of Cr oxide were measured using a non-conventional spectrometer. Theoretical spectra were obtained using the DV-Xα method in order to interpret the Kβ spectrum structures. Kβ spectrum structures were analyzed and spectral parameters show a great sensitivity to the oxidation state and to the Cr-O distance. High-purity samples of CrO₂ were obtained by means of thermal treatment at 513 °C under oxygen pressure of 200 bar. X-ray diffraction patterns show a typical rutile structure, without spurious phases. The CrO₂ data allowed to confirm the linear dependency of the Kβ_1,3 and Kβ_2,5 energy positions with the oxidation state. The energy of the Kβ_2,5 line relative to the Kβ_1,3 line seems to be a suitable parameter for characterization of the oxidation state. The relative Kβ″ transition probability per Cr-O falls exponentially with Cr-O increasing distance. This behaviour was not found in the literature for Cr oxides.     

Spectroscopic and magnetic studies of manganese ions in ZnO-Sb2O3-B2O3 glass system

ZnO-Sb₂O₃-B₂O₃ glasses containing different concentrations of MnO ranging from 0 to 1.0 mol% were prepared. A number of studies, viz. optical absorption, infrared and ESR spectra and magnetic susceptibility, were carried out as a function of manganese ion concentration. The analysis of the results indicate that manganese ions mostly exist in Mn²⁺ state in these glasses when the concentration of MnO≤0.6 mol% and above this concentration, these ions seem to exist in Mn³⁺ state in the glass network.     

Determination of the low energy values of CH4 transitions in the 2ν3 region near 1.66 μm from absorption spectra at 296 and 81 K

The high resolution absorption spectra of ¹³CH₄ were recorded at 81 K by differential absorption spectroscopy using a cryogenic cell and a series of distributed feed back (DFB) diode lasers and at room temperature by Fourier transform spectroscopy. The investigated spectral region corresponds to the high energy part of the ¹³CH₄ tetradecad dominated by the 2ν₃ overtone near 5988 cm⁻¹. Empirical line lists were constructed containing, respectively, 1629 ¹³CH₄ transitions detected at 81 K (5852-6124 cm⁻¹) and 3481 features (including 85 lines of ¹²CH₄) measured at room temperature (5850-6150 cm⁻¹); the smallest measured intensities are about 3 × 10⁻²⁶ and 4 × 10⁻²⁵ cm/molecule at 81 and 296 K, respectively. The lower state energy values were derived for 1196 ¹³CH₄ transitions from the variation of the line intensities between 81 and 296 K. These transitions represent 99.2% and 84.6% of the total absorbance in the region, at 81 and 296 K, respectively. Over 400 additional weak features were measured at 81 K and could not be matched to lines observed at room temperature. The quality of the resulting empirical low energy values is demonstrated by the excellent agreement with the already-assigned transitions and the clear propensity of the empirical low J values to be close to integers. The two line lists at 81 and at 296 K provided as Supplementary material will enable future theoretical analyses of the upper ¹³CH₄ tetradecad.     

Multispectrum analysis of CH4 from 4100 to 4635 cm: 1. Self-broadening coefficients (widths and shifts)

The Lorentz self-broadening (halfwidths) and self-induced pressure-shift coefficients were measured for the first time in the octad region of methane. All spectra were recorded at 0.011 cm⁻¹ resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. ¹²C-enriched CH₄ gas samples at room temperature were used, and high signal-to-noise ratios of 2000:1 were achieved. The multispectrum nonlinear least squares fitting technique enabled us to fit simultaneously a total of 10 high-resolution laboratory absorption spectra consisting of six self-broadened and four air-broadened spectra. In this paper, we report the self-broadened widths and self-induced pressure shift coefficients for 1423 transitions belonging to five bands with a maximum J of 16. The numbers of measurements by bands are: 71 for ν₂ + 2ν₄, 202 for ν₁ + ν₄, 824 for ν₃ + ν₄, 58 for 2ν₂ + ν₄, and 268 for ν₂ + ν₃. The observed widths varied from 0.045 to about 0.090 cm⁻¹ atm⁻¹ at 296 K. The measured pressure-shift coefficients had values extending from about −0.020 to −0.005 cm⁻¹ atm⁻¹ at 298.3 ± 1.2 K. The results obtained for the broadening coefficients in the various bands were compared with each other and with measurements reported in the literature for other methane bands.     

Temperature-dependent fluorescence characteristics of an ytterbium-sensitized erbium-doped tellurite glass

In this article, the 1.5 μm emission spectra corresponding to the ⁴I_13/2→⁴I_15/2 transition of Er³⁺ in tellurite glass are studied within the temperature from 8 to 300 K. The emission spectra of Er³⁺: ⁴I_13/2→⁴I_15/2 transition are also analyzed using a peak-fit routine, and an equivalent four-level system is proposed to estimate the stark splitting for the ⁴I_15/2 and ⁴I_13/2 levels of Er³⁺ in the tellurite glass. The results indicate that the ⁴I_13/2→⁴I_15/2 emission of Er³⁺ can exhibit a considerable broadening due to a significant enhance the peak a′, and b′ change, respectively, and the peaks of which are located at about 1507 and 1556 nm. A detailed study of temperature-dependent 1.5 μm emission spectra involving the change of the corresponding sub-bands shows that as the temperature decreases from 300 to 8 K, its line-shape becomes sharper and more intense (the full-width at half-maximum decreases from 59 to 38 nm). Temperature-dependent fluorescence intensities and the experimentally determined lifetimes are investigated; the results show that a decrease behavior of fluorescence intensities and lifetimes are observed for temperature from 8 to 300 K.     

Studies on the origins of the absorption spectra in PbWO4 crystal

The electronic structures and absorption spectra for both the perfect PbWO₄ (PWO) crystal and the three types of PWO crystals, containing V_Pb²⁻, V_O²⁺ and a pair of V_Pb²⁻-V_O²⁺, respectively, have been calculated using CASTEP codes with the lattice structure optimized. The calculated absorption spectra indicate that the perfect PWO crystal does not occur absorption band in the visible and near-ultraviolet region. The absorption spectra of the PWO crystal containing V_Pb²⁻ exhibit seven peaks located at 1.72 eV (720 nm), 2.16 eV (570 nm), 2.81 eV (440 nm), 3.01 eV (410 nm), 3.36 eV (365 nm), 3.70 eV (335 nm) and 4.0 eV (310 nm), respectively. The absorption spectra of the PWO crystal containing V_O²⁺ occur two peaks located at 370 nm and 420 nm. The PWO crystal containing a pair of V_Pb²⁻-V_O²⁺ does not occur absorption band in the visible and near-ultraviolet region. This leads to the conclusions that the 370 and 420 nm absorption bands are related to the existence of both V_Pb²⁻ and V_O²⁺ in the PWO crystal and the other absorption bands are related to the existence of the V_Pb²⁻ in the PWO crystal. The existence of the pair of V_Pb²⁻-V_O²⁺ has no visible effects on the optical properties. The calculated polarized optical properties are well consistent with the experimental results.     

Collision-induced first overtone band of D2 in binary mixtures D2-X where X is Ar, Kr, and Xe

Enhancement spectra of the collision-induced absorption in the first overtone region 5500-6750 cm⁻¹ of D₂ in the D₂-Ar, D₂-Kr, and D₂-Xe binary mixtures were studied at 298 K for base densities of D₂ in the range 55-251 amagat and for partial densities of Ar, Kr, and Xe in the range 46-384 amagat. The observed spectra consist of the following quadrupolar transitions: O₂(3), O₂(2), Q₂ (J), J = 1-5 and S₂ (J), J = 0-5 of D₂. Binary and ternary absorption coefficients were determined from the integrated absorption coefficients of the band. Profile analyses of the spectra were carried out using the Birnbaum-Cohen (BC) lineshape function and characteristic lineshape parameters were determined from the analyses.     

Magnetic behavior of MnCo2O4+δ spinel obtained by thermal decomposition of binary oxalates

Manganese cobaltites MnCo₂O_4.62 and MnCo₂O_4.275 having a spinel structure were studied by measuring magnetization, AC susceptibility and by XANES spectroscopy. These compounds were synthesized by decomposition of the binary oxalate Mn_1/3Co_2/3C₂O₄·2H₂O in air at 220 and 500 °C, respectively. It was found that the differences in magnetic characteristics of these cation-deficient spinels are due mainly to variations in the degree of oxidation of manganese. It was shown that the complex oxide MnCo₂O_4.62 formed right after decomposition of the binary oxalate contains about 5×10⁻⁴ mass% metallic cobalt, which determines the dependence of magnetic susceptibility χ on the magnetic field at 300 K. The magnetic transition peculiar to the stoichiometric spinel MnCo₂O₄ at 183 K decreases to 167.5 K for MnCo₂O_4.275 and 67.5 K for MnCo₂O_4.62.     

Effects of Gd and Lu co-doping on the long afterglow properties of yellowish-orange phosphor Y2O2S:Ti, Mg

A new long afterglow phosphor Y₂O₂S:Ti⁴⁺, Mg²⁺ co-doped with Gd³⁺ and Lu³⁺ was synthesized by solid-state reaction in inert gas ambient. Its properties were systematically analyzed by X-ray diffraction (XRD), luminescence spectra, afterglow decay curves and thermoluminescence (TL) spectra. It was found that the long afterglow performance of Y₂O₂S:Ti⁴⁺, Mg²⁺ such as brightness and persistent time was largely improved when co-doped with Gd³⁺ and Lu³⁺. By analyzing the TL curve the activation energy E were calculated to be 0.64 eV for 388 K peak and 0.98 eV for 508 K peak, and the trap intensity related to 388 K peak is much stronger than that related to 508 K peak. The mechanism of the long afterglow was also discussed in this paper.     

Line mixing effects in the ν2 + ν3 band of methane

This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν₂ + ν₃ band of ¹²CH₄. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν₂ + ν₃ transitions between 4410 and 4629 cm⁻¹ are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm⁻¹ atm⁻¹ at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm⁻¹ atm⁻¹ at 296 K.