Method for fitting crystal field parameters and the energy level fitting for Yb3+ in crystal Sc2O3

<正>A method to compute the numerical derivative of eigenvalues of parameterized crystal field Hamiltonian matrix is given,based on the numerical derivatives the general iteration methods such as Levenberg-Marquardt,Newton method, and so on,can be used to solve crystal field parameters by fitting to experimental energy levels.With the numerical eigenvalue derivative,a detailed iteration algorithm to compute crystal field parameters by fitting experimental energy levels has also been described.This method is used to compute the crystal parameters of Yb~(3+) in Sc_2O_3 crystal, which is prepared by a co-precipitation method and whose structure was refined by Rietveld method.By fitting on the parameters of a simple overlap model of crystal field,the results show that the new method can fit the crystal field energy splitting with fast convergence and good stability.     

Magnetic Resonance and Optical Spectroscopy of Yb<Superscript>3+</Superscript> in CsCaF<Subscript>3</Subscript> Single Crystal: an Analysis of Distortions of the Crystal Lattice near Yb<Superscript>3+</Superscript>

A trigonal Yb³⁺ paramagnetic center in the CsCaF₃ single crystal was studied by magnetic resonance and optical spectroscopy methods. The structural model of the complex and the empirical energy level scheme were established. The transferred hyperfine interaction parameters and the crystal field ones were determined. The crystal field parameters were used to analyze the lattice distortions in the vicinity of Yb³⁺ using the superposition model.     

悬浮区域熔炼法制备LaB6单晶体与发射性能研究

采用区域熔炼法成功制备出了高质量,高纯度,大尺寸的LaB₆单晶体. 系统分析了制备过程中每个参数对LaB₆单晶生长的影响,确定了晶体生长最佳工艺为:样品转速为30 r/min,生长速度为8-10 mm/h. 分析了单晶LaB₆ (100) 晶面的热电子发射性能,结果表明,当阴极温度为1873 K时,最大热发射电流密度为44.36 A/cm²;利用 Richardson 直线法求出了绝对零度逸出功和有效逸出功分别为1.99和2.59 eV. 场发射测试结果表明,单晶LaB₆场发射单尖最大场发射电流密度达到4.9×10⁶ A/cm²,场发射因子为41500 cm^-1,表现出良好的场发射性能. 因此单晶LaB₆作为热阴极和冷阴极都具有很广阔的应用前景. 关键词： 区域熔炼法 6')" href="#">单晶LaB₆ 热发射性能 场发射性能     

Nephelauxetic effect for the isoelectronic 3d-ions (Cr, Mn, Fe) in SrTiO3

The exchange charge model of crystal field theory has been used to analyze systematically the ground state absorption spectra of isoelectronic Cr³⁺, Mn⁴⁺, and Fe⁵⁺ ions in an octahedral coordination in the SrTiO₃ crystal. The parameters of the crystal field acting on the valence electrons of impurity ions are calculated from the available crystal structure data. A special attention is paid to the analysis of dependencies of the crystal field invariants and covalence effects on the impurity ion. It is shown numerically that the covalence effects between the above impurity ions and ligands increase with an increase of the 3d-ion oxidation state.     

Magnetic interactions in Pr3+ : LiYF4 for quantum manipulation : search for an efficient three-level Λ system

The influence of an external magnetic field on the hyperfine structure of the ³ H₄(0) and ¹D₂(0) crystal field states of Pr³⁺ in LiYF₄ is studied in order to find an efficient three-level Λ system. Using an experimentally determined spin Hamiltonian, we show that three-level Λ systems can be obtained with equal strengths for the optically excited transitions under various magnetic field magnitudes and orientations. An analytical analysis based on two levels is proposed to find useful magnetic fields without extensive numerical calculations and to understand the general behaviour of the system. Pr³⁺ hyperfine structure has also been directly calculated using a complete Hamiltonian including free ion, crystal field and magnetic interactions. A good agreement with the spin Hamiltonian approach is found for the ground state whereas the excited state results poorly reproduce the experiment. This is attributed to the low accuracy of ¹D₂ crystal field wavefunctions. This suggests that transition strengths ratios could be calculated directly from the crystal field Hamiltonian with improved crystal field parameters.     

Electronic absorption spectrum of cobalt antipyrine complex

The electronic absorption spectrum of cobalt antipyrine complex in the form of a single crystal is studied both at laboratory and liquid nitrogen temperatures. The spectrum is characteristic of Co²⁺ ion in an octahedral crystal field with bands exhibiting spin-orbit splittings at liquid nitrogen temperature. A good fit is obtained with the following crystal field parameters. B = 0.85 kK, C = 37.00 kK, Dq = 0.84 kK, ζ = 0.50 kK.     

Nd3+:Gd3Sc2Al3O12 晶场能级及拟合

Nd³⁺ :GSAG是性能优良的942 nm激光晶体.用提拉法成功生长Nd³⁺ :GSAG单晶,研究其室温透射光谱,辨认位置高达29967 cm^-1的68个Nd³⁺晶场能级.对这些能级拟合了自由离子及晶场Hamilton参量,拟合标准偏差为16.7 cm^-1,表明实验与计算能级符合很好.获得的Hamilton参量可用于计算Nd³⁺ :GSAG中Nd³⁺的     

Determination of physical parameters in 4f–3d intermetallics by rare earth Mössbauer spectroscopy

From¹⁶¹Dy,¹⁶⁶Er and¹⁶⁹Tm Mössbauer spectroscopy measurements magnetic moments, magnetic coupling constants and crystal field parameters can be determined. A comparison with results of other techniques will be made.     

Mössbauer spectra of a paramagnetic ion in an axial crystal field in the presence of spin-lattice relaxation

The influence of spin-lattice relaxation on the Mössbauer hyperfine spectra of the Fe³⁺ ion is investigated in the case of an axial crystal field. All the various influences of the relaxation process on the spectra can be explicitly described using two relaxation parameters. A detailed analysis of the Mössbauer relaxation spectra for the various temperatures, relations between the relaxation parameters and external magnetic field directions is carried out. When the magnetic field direction is nearly collinear with the symmetry axis and one of the relaxation parameters is small, the dynamics of Mössbauer spectra is shown to have anomalous features. The influence of random magnetic fields is shown to give an unconventional development of patterns as a function of the relaxation parameters.     

EPR,optical absorption and superposition model studies of Fe3+-doped cesium chloride single crystals: a case of substitutional as well as interstitial sites

An electron paramagnetic resonance study of Fe³⁺-doped cesium chloride single crystals was carried out at room temperature. Three sites are observed. The spin Hamiltonian parameters were determined from the angular variation of the observed resonance lines. The hyperfine structure is observed due to the presence of Fe⁵⁷ centers. At site I, Fe³⁺ enters the lattice substitutionally, replacing Cs⁺ in the cubic symmetry of the crystal, whereas at sites II and III, Fe³⁺ enters the lattice interstitially. The local site symmetry of Fe³⁺ in the host lattice is considered to be orthorhombic. An optical absorption study of the crystal was also performed at room temperature. The observed bands were assigned and the Racah inter-electronic repulsion parameters (B and C) and the cubic crystal field splitting parameter (Dq) were determined. On the basis of EPR and optical data, the nature of the metal–ligand bonding in the crystal was determined. The crystal field parameters were evaluated using the superposition model and then used in the microscopic spin Hamiltonian and perturbation equations to determine the zero-field splitting parameters (ZFSPs) theoretically for all sites observed. The theoretical ZFSPs are in good agreement with the experimental values.     

Crystal field at the impurity center sites in ionic crystals

Perturbation theory is developed for second-quantized operators in a basis of partly nonorthogonal orbitals. This method may be helpful in carrying out ab initio calculations of the parameters of the crystal field at the impurity center sites. As an illustration, when estimating the crystal field parameters for Yb³⁺: KZnF₃, some fitting parameters are calculated using this method. The results agree well with experimental data, which indicates that this theory shows considerable promise.     

EPR,optical and superposition model study of Mn2+ doped L+ glutamic acid

Electron paramagnetic resonance (EPR) study of Mn²⁺ doped L+ glutamic acid single crystal is done at room temperature. Four interstitial sites are observed and the spin Hamiltonian parameters are calculated with the help of large number of resonant lines for various angular positions of external magnetic field. The optical absorption study is also done at room temperature. The energy values for different orbital levels are calculated, and observed bands are assigned as transitions from ⁶A_1g(s) ground state to various excited states. With the help of these assigned bands, Racah inter–electronic repulsion parameters B = 869 cm^?1, C = 2080 cm^?1 and cubic crystal field splitting parameter Dq = 730 cm^?1 are calculated. Zero field splitting (ZFS) parameters D and E are calculated by the perturbation formulae and crystal field parameters obtained using superposition model. The calculated values of ZFS parameters are in good agreement with the experimental values obtained by EPR.     

Spectral line intensities of Yb3+ ion in LiNbO3 crystals

Optical spectra of absorption and luminescence of LiNbO₃:Yb³⁺ crystals are investigated experimentally and theoretically. Within the framework of the point charge approximation of crystal field, the Stark problem is solved: crystal field parameters and wave functions of Stark states are determined. Line strengths due to indirect electric-dipole and magnetic-dipole inter-Stark transitions are calculated and values of the Judd-Ofelt parameters are determined. Values of the branching ratios of luminescence. Einstein coefficients and, lifetime of the excited sublevel are calculated. A satisfactory agreement of calculated results with experimental data is obtained.     

Pressure effect on emission spectra and crystal field for La OBr : Eu

Abstract

The emission spectra for LaOBr : Eu were measured at pressures up to 13 GPa and room temperature. The pressure dependences of levels of ⁷F_0,1,2,3,4 and ⁵D_0,1,2 are given. The crystal field parameters B^k _q were computed by fitting the experimental levels. The strength of crystal field decreases with increasing pressure. A brief discussion on the observed phenomena is presented.     

Magnetic properties of ErIG and approximation of isotropic exchange

A one-ion model calculation which considers the Er³⁺ ion subject to the crystal field, the isotropic exchange field and the applied magnetic field is compared with the following experimental data: the easy axis direction, the transition temperature, the temperature and field dependence of the magnetization, the compensation temperature, the magnetocrystalline anisotropy and the umbrella structure of Er³⁺ magnetic moments in ErIG. The crystal field parameters in Y(Er)GG and ErGG are discussed and determined first. The same parameters are used for ErIG, only those of second order are allowed to vary. In spite of the isotropic exchange approximation, the experiments (except the controversial umbrella structure and anisotropy data) are well reproduced within the framework of this model. Further improvements are expected by inclusion of the anisotropy of the exchange interaction.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.     

Interpretation of the optical and EPR spectra of the Cr<Superscript>3+</Superscript> ion in a lithium niobate crystal

The optical and EPR spectra of the Cr³⁺ γ-center in a lithium niobate crystal are interpreted, and the energy levels of the ground-state spin quadruplet and all the experimentally revealed doublet states are described. The parameters of the Coulomb Hamiltonian for the spin-orbit interaction of electrons and their interaction with an electrostatic field of the crystal are determined. It is found that the crystal field acting on the paramagnetic ion is relatively strong and has trigonal symmetry. The Cr³⁺ ion embedded in the crystal is characterized by considerable changes in the interactions associated with the excited configurations.     

Crystal fields of Pr in LiYF4 under pressure

Fluorescence spectra of LiYF₄:Pr³⁺ have been measured between 12,000 and 22,000 cm⁻¹ under pressures up to 10 GPa. In total, 25 crystal field energy levels were obtained and used for the determination of free-ion and crystal field parameters under pressure. According to the nephelauxetic effect, the free-ion parameters decrease with increasing pressure. The relative decrease is larger for the Slater than for the spin-orbit coupling parameter. This behavior is consistent with former studies on Pr³⁺ in different crystals and can be explained by a special covalency model. According to an effective D_2d symmetry, five crystal field parameters B₀²(f,f), B₀⁴(f,f), B₄⁴(f,f), B₀⁶(f,f), and B₄⁶(f,f) are non-zero. The pressure-induced changes of these parameters have been determined up to the maximum pressure of 10 GPa. In order to improve the calculation of the crystal field levels, the configuration interactions with the 4f¹6p¹ configuration have been taken into account. The effect of these interactions are also analyzed under pressure and distinct improvements of the energy level calculations have been obtained.     

BaCl2中Eu2+的电子自旋共振研究

制备和用X射线分析BaCl₂:Eu微晶的结构,并测量它的电子自旋共振(ESR)谱,结构分析和ESR谱都表明,替代Ba²⁺的Eu²⁺离子是处在轴对称的正交晶场中;并用抽对称的自旋哈密顿量和晶场哈密顿量对ESR实验数据进行拟合,求得在正交对称的BaCl₂中的Eu²⁺的自旋哈密顿参数;还发现Eu替代Ba²⁺的掺杂浓度的饱和值为0.34mol％。 关键词：     

Electron paramagnetic resonance of Gd3+ ions in powders of LaF3:Gd3+ nanocrystals

The observation of electron paramagnetic resonance of Gd³⁺ ions in nanosized powders of rare-earth fluorides LaF₃:Gd³⁺ has been reported. The measurements have been performed on a single crystal and micro- and nanosized powders at room temperature. Electron paramagnetic resonance spectra and spin-Hamiltonian parameters of Gd³⁺ ions have been obtained. A qualitative difference of spectra in nano- and micropowders due to the increase in the spread of the crystal field parameters with the decrease in the particle size has been found. The relationship between the single-crystal domain size and the hydrothermal treatment time has been established.