GeFe2O4晶体的基态能级和零场分裂参量

GeFe₂O₄是一种单晶化合物，考虑到由3个〈111〉方向之一的一个 轴，从一个中心位置 到另一个中心位置之间，以Fe²⁺离子为中心离子和O^2-为配体构 成了三角（C 3v）对称体系.利用不可约张量理论，建立了3d⁴/3d⁶离子三角（C3 v）对称的晶体场和 自旋相互作用哈密顿矩阵，因此，由完全对角化的晶体场和自旋-轨道相互作用哈密顿矩阵 和电子顺磁共振理论公式求出单晶GeFe₂O₄中Fe²⁺离子 的电子顺磁共振零场分 裂参量D和F-a.并研究了自旋三重态对电子顺磁共振（EPR）零场分裂的贡献.结果显示自旋 三重态对基态零场分裂的贡献是较强的，理论计算结果与实验值相符. 关键词： 自旋三重态 晶体场 低自旋态 高自旋态 零场分裂     

An O23− radiation defect in AlPO4 and GaPO4

Hole centers with C₂ site symmetry, very similar g-matrices and small hyperfine splittings due to two nuclei with $\text{I =}\text{1}\text{2}$ were detected and analyzed by EPR in synthetic single crystals of AlPO₄ and GaPO₄ after X-ray irradiation. A very similar center, but without any detectable hyperfine splitting, was reported in natural quartz. These centers are ascribed to O₂^3? ions with two equivalent ³¹P nuclei as the source of the hyperfine splitting in the phosphates. This hyperfine splitting is considerably smaller than for O? adjacent to phosphorous (i.e. PO₄^2? centers). The electronic structures of these defects are discussed and compared with those reported for the same centers in other compounds.     

High-Resolution IR Spectroscopy of the N2O-H2O and N2O-D2O van der Waals Complexes

We report high-resolution infrared vibrational-rotational spectra of the weakly bound complexes N₂O-H₂O and N₂O-D₂O in the higher frequency N₂O stretching mode region (ν₃=2223.756693(124) cm⁻¹). The measurements were carried out using a free jet expansion in combination with a lead salt diode laser spectrometer. Rotational constants, quartic centrifugal distortion constants, and band origins have been derived for both isotopomers. The geometrical structure is determined using isotopic substitution. The deduced structure shows evidence for a second hydrogen bond interaction within the complex. The nonrigidity of the complexes gives rise to an internal rotation of the water molecule around its own C_2v symmetry axis. For N₂O-H₂O, a tunneling splitting arising from this internal motion has been observed in the spectra. According to symmetry considerations, the observed splitting in the spectrum of N₂O-H₂O corresponds to the difference between the tunneling frequencies in the ground and vibrationally excited states.     

Bifunctional photocatalysis of TiO2/Cu2O composite under visible light: Ti in organic pollutant degradation and water splitting

Photocatalytic experiment results under visible light demonstrate that both TiO₂ and Cu₂O have low activity for brilliant red X-3B degradation and neither can produce H₂ from water splitting. In comparison, TiO₂/Cu₂O composite can do the both efficiently. Further investigation shows that the formation of Ti³⁺ under visible light has great contribution. The mechanism of photocatalytic reaction is proposed based on energy band theory and experimental results. The photogenerated electrons from Cu₂O were captured by Ti⁴⁺ ions in TiO₂ and Ti⁴⁺ ions were further reduced to Ti³⁺ ions. Thus, the photogenerated electrons were stored in Ti³⁺ ions as the form of energy. These electrons trapped in Ti³⁺ can be released if a suitable electron acceptor is present. So, the electrons can be transferred to the interface between the composite and solution to participate in photocatalytic reaction. XPS spectra of TiO₂/Cu₂O composite before and after visible light irradiation were carried out and provided evidence for the presence of Ti³⁺. The image of high-resolution transmission electron microscopy demonstrates that TiO₂ combines with Cu₂O tightly. So, the photogenerated electrons can be transferred from Cu₂O to TiO₂.     

Spectre d'absorption et effet Zeeman de l'ion Mn2+ dans un sulfate acide de manganese et de potassium MnK4H2(SO4)4, 2H2O a basse temperature

We present aborption spectra of an oriented single crystal of MnK₄H₂(SO₄)₄, 2H₂O at temperatures between 20 and 1.6 K. This salt has orthorhombic symmetry and gives, both in the visible and ultraviolet regions, an absorption spectrum which changes considerably when the temperature decreases from 20 to 4.2 K. The spectrum has sharp lines at 1.6 K in the two absorption regions corresponding to teh excited levels ⁴A₁⁴E(⁴G) and ⁴T₂(⁴D). A study has been made of the Zeeman splitting of these sharp lines; a discontinuity has been observed in the Zeeman splitting as a function of magnetic field at 1.6 K. This discontinuity is a consequence of a magnetically-ordered phase.     

BeAl2O4:Cr3+的晶场能级

金绿宝石中镜对称格位上Cr³⁺(Ⅱ)离子的⁴T₂,⁴T₁和²E能级与该材料的激光运转有关。⁴T₂和⁴T₁能级各分裂成三个子能级。为从偏振吸收谱上确定BeAl₂O₄:Cr³⁺的能级图,本文计算了⁴T₂和⁴T₁的分裂,找到了对谱方法,得到了表征能级分裂的参量K_{1和K2的值。最后给出了以低点群不可约表示标号的、BeAl2O4:Cr³⁺(Ⅱ)的晶场能级图。 关键词：}     

Spectral holeburning and the Stark and Zeeman effects in SrF2:Sm2+

We have observed narrow (40 MHz) persistent spectral holeburning in SrF₂:Sm²⁺ for Sm²⁺ ions in perturbed cubic sites. The transition studied is ⁷F₀?⁵D₀ between the f-electron states. Stark effect measurements show a linear splitting with a coefficient of 0.006 MHz/V cm^-1 and the splitting pattern shows that the site has C_4V symmetry. The C_4V perturbation is very weak and leads to unresolved splittings of cubic T_1g levels of ～2 cm^-1. The nonlinear Zeeman effect was studied using holeburning and the coefficient of 1.04 Hz/G² shows that the predominant magnetic coupling is in the ground state as found recently for CaF₂:Sm²⁺.     

Structural study of the Lu2Si2O7-Sc2Si2O7 system

Different compositions in the Lu₂Si₂O₇-Sc₂Si₂O₇ system have been synthesized following the ceramic method. All XRD patterns are compatible with the thortveitite structure (β-RE₂Si₂O₇ polymorph). Unit cell parameters change linearly with composition, which indicates a complete solid solubility of Sc₂Si₂O₇ in Lu₂Si₂O₇. ²⁹Si MAS NMR spectra show a decrease of the ²⁹Si chemical shift with increasing Sc content. A correlation reported in the literature to predict ²⁹Si chemical shifts in silicates is applied here to obtain the theoretical variation in ²⁹Si chemical shift values in the system Lu₂Si₂O₇-Sc₂Si₂O₇ and the results compare favourably with the values obtained experimentally. The FWHM values of the ²⁹Si MAS NMR curves indicate a random distribution of Lu and Sc in the structure of the intermediate members. Finally, the IR study of the system confirms the solubility of Sc₂Si₂O₇ in Lu₂Si₂O₇, showing the splitting of several modes in the intermediate members and a linear shift of the frequency on going from one end-member to the other.     

Time-resolved luminescence of UO2MoO4

Time-resolved spectroscopy and decay-time measurements for the intrinsic and trap emission lines of UO₂MoO₄ supply experimental evidence for fast energy migration among intrinsic centres and from intrinsic to trap centres. The temperature behaviour of the decay time for the main trap lines reveals an energy transfer rate from trap to intrinsic centres in the order of 5×10⁹s^-1, while the transfer rate among intrinsic centres, as estimated from the correlation field splitting, is 3×10¹¹ s^-1.     

Low-temperature Mössbauer studies of FeNb2O6

Fe⁵⁷ Mössbauer spectra of FeNb₂O₆ were obtained from 15.0K down to 1.9 K. The isomer shift, 1.42±0.01 mm sec^?1 relative to Cr, was found to be temperature independent, whereas the magnitude of the quadrupole splitting was observed to decrease slightly with temperature. The quadrupole splitting and the hyperfine field at 1.9 K are -2.41±0.01 mm sec^?1 and 34.6±0.3 kOe respectively. The directions of the hyperfine fields experienced by the Fe nuclei are in the a-c plane symmetrically displaced with respect to the crystallographic axes.     

Luminescence as an indication of distortion in A3+2 B4+2 O7 type pyrochlores

The Eu³⁺ luminescent emission spectra of rare-earth titanate, titanate-stannate, stannate, hafnate and zirconate pyrochlores, A³⁺₂B⁴⁺₂O₇, indicated that a linear relationship existed between the splitting of the ⁵D₀ → ⁷F₁ magnetic-dipole transition and the size of the cation present. Small A³⁺ cations and larger B⁴⁺ cations both produced a lattice with a lesser degree of deviation from O_h symmetry.     

Analytical potential energy function for the electronic states 2^∏1/2 and 2^∏3/2 of O^x2 （x=＋1, -1）

The splitting of potential energy levels for ground state X^2∏g of O^x2 （x = ＋1,-1） under spin-orbit coupling （SOC） has been calculated by using the spin-orbit （SO） multi-configuration quasi-degenerate perturbation theory （SO-MCQDPT）. Their Murrell-Sorbie （M S） potential functions are gained, and then the spectroscopic constants for electronic states 2^∏1/2 and 2^∏3/2 are derived from the M S function. The vertical excitation energies for O^x2 （x = ＋1,-1） are v[O2＋1^（2∏3/2→X^2∏1/2）] =195.652cm^-1, and v[O2^-1（2^∏1/2 →X^2∏3/2）] =182.568cm^-1, respectively. All the spectroscopic data for electronic states 2^∏1/2 and 2^∏3/2 are given for the first time.     

Electron localization in Fe2PO5

Fe₂PO₅ is a mixed valence compound where Fe^II and Fe^III are in face sharing octahedra with a short Fe^II - Fe^III distance, so that electron delocalization along chains parallel to the $\text{b}$ axis of the orthorhombic cell was worth to investigate. From Mössbauer experiments, carried out up to 600°C, it appears that the 4 lines spectra evolution, as regards Isomer Shift, Quadrupolar Splitting, and Linewidth, is only consistent with a localized electron pattern. This result is interpreted from the unequivalence of the 2 sites. The strong Fe^II quadrupolar splitting decrease allows the determination of the energy gap between the d_xy and d_yz-d_zx orbitals.     

AgGaSe2 : A highly photoconductive material

High resistivity single crystals of AgGaSe₂ were grown by the horizontal Bridgman technique. The near band edge photoconductivity of the grown crystal at room temperature was found to be up to 2×10⁴ times higher than the dark conductivity, under the illumination of 10⁻³ W/cm². The photoconductivity spectrum consists primarily of three peaks, which are attributed to the transitions from Γ₇(A), Γ₆(B) and Γ₇(C) states of valence band to the conduction band Γ₆. The crystal field splitting and the spin-orbit splitting were determined from these peak energy positions of the photoconductivity spectrum.     

Hyperfine interaction of d-electrons in the amorphous semiconductors MoO3-TeO2 and MoO3-P2O5

ESR spectra of the amorphous semiconducting systems MoO₃-TeO₂ and MoO₃-P₂O₅ are presented. The occurence of a hyperfine splitting is confirmed by numerical simulations of the observed spectra and by enriching with the isotope Mo⁹⁵. The isotropic hyperfine field at the molybdenum nucleus amounts to (113±10) kG at high MoO₃ concentration. This value is compared with results of measurements on crystalline MoO₃.     

四角对称晶场中4B1(3d3)态离子的磁相互作用及其自旋哈密顿参量研究

基于完全对角化方法，研究了⁴B₁(3d³)态 离子在四角对称晶场中的磁相互作用，分析了自旋哈密顿参量(b⁰₂, g_∥, g_⊥ , Δg)的微观起源.结果表明 ：在被考虑的大部分晶场区域，人们通常考虑的SO(spin-orbit)磁相互作用的贡献最为重要 ；然而，对于零场分裂参量b⁰₂而言，来自其他机理(包 括SS(spin-orbit)，SOO(sp in-other-orbit)，SO-SS-SOO)的贡献在大部分晶场区域超过了20％；在部分晶场区域，其 他机理的贡献甚至超过SO机理的贡献.详细地分析了Macfarlane 零场分裂参量b^{0₂ 近似三阶微扰理论的收敛性，结果表明：该理论在大部分晶场区域收敛性较差.讨论了3d3}态离子第一激发态²E_g分裂的微观起源.并利用 群论方法解 释了在C_4v和C_3v对称晶场中²E_{g< /sub>态分裂的不同机理. 关键词： 4B1(3d³)态离子')" href="#">⁴B1(3d³)态离子 磁相互作用 自旋哈密 顿参量 完全对角化方法(CDM) 微扰理论方法(PTM)}     

Photoluminescence of Eu in SrGa2S4

A photoluminescence (PL) study of the green-emitting SrGa₂S₄:Eu²⁺ phosphor is reported. Diffuse reflectance, excitation, and emission spectra were examined with the aim to enlarge the fundamental knowledge about the emission of the Eu²⁺ ion in this lattice. The thermal dependence of the radiative properties was investigated. In particular, the Stokes shift, the crystal field splitting and the activation energy of the thermal quenching were determined. By combining these results with the information presented in literature, we discussed the location of the Eu²⁺ levels relative to the valence and conduction bands of SrGa₂S₄.     

Theoretical calculations of the optical band positions and spin-Hamiltonian parameters for Cr ions in Y2Ti2O7 crystal

The optical band positions and spin-Hamiltonian parameters (g factors g_g_? and zero-field splitting D) for the trigonal Cr³⁺ centers in Y₂Ti₂O₇ crystal are calculated from the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model. In the calculations, the contributions to spectral data from both the spin-orbit parameter of central dⁿ ion and that of ligand ion are considered and the crystal field parameters used are estimated from the superposition model. The calculated results are in reasonable agreement with the experimental values. The defect structures of Cr³⁺ center is suggested.     

A 57Fe Mössbauer study of four pyrite compounds: CoS2, NiS2, CoSe2 and NiSe2

Mössbauer spectra of ⁵⁷Fe-doped CoS₂, NiS₂, CoSe₂ and NiSe₂ have been taken at various temperatures between 300 and 16 K, and the hyperfine parameters H and θ measured for those substances showing magnetic hyperfine splitting. Quadrupole splitting $\text{QS}\text{(=}\text{1}\text{2}\text{e}{}^2\text{qQ)}$ was also measured and for NiS₂ and CoS₂ the sign of QS was determined.The room temperature value of QS showed a similar behaviour in the series FeS₂CoS₂NiS₂ to that in the series FeSe₂CoSe₂NiSe₂. The absolute value of QS decreased slightly below the magnetic transition temperature in those compounds which showed magnetic ordering.     

Shubnikov-de haas effect in n-CdSnAs2

Shubnikov-de Haas oscillations in the transverse magnetoresistance of single-crystalline n-type CdSnAs₂ have been recorded at temperatures between 2 and 25 K in magnetic fields up to 5T. The electron concentration of the samples ranged from 2 × 10¹⁷ to 2 × 10¹⁸ cm^?3. The angular dependences of the oscillation periods and cyclotron effective masses showed that the conduction band exhibits an energy dependent anisotropy, obeying the Kildal band structure model. For the low-temperature values of the band parameters we found: a band gap E_g = 0.30 eV, a spin-orbit splitting Δ = 0.50 eV, a crystal field splitting parameter δ = ?0.09 eV, and an interband matrix element P = 8.5 × 10^?8eV cm. This simple four-level model was found to be not adequate to describe quantitatively the observed electronic effective g-factor for a sample with low electron concentration.