Investigation of local lattice structure around Cr3+ ions at the trigonal and tetragonal sites in RbCdF3: Cr3+ crystal

The local lattice structure and EPR, optical spectra for Cr³⁺ doped in RbCdF₃ crystal have been studied by diagonalizing the complete energy matrices. The results show that the local structure of the Cr³⁺ ions in RbCdF₃ exhibits a compressed distortion at the trigonal and tetragonal sites. The compressed distortion can be ascribed to the fact that the radius of Cr³⁺ ion is smaller than that of Cd²⁺ ion, and therefore Cr³⁺ ion will draw the fluorin ligands inwards. The variational ranges of the local structural parameters for Cr³⁺ doped in RbCdF₃ crystal R =?1.9491 Å ～?1.9814 Å, θ?= 55.234° ～?55.286° at the trigonal site and R ₁ =?1.8617 Å ～?1.8928 Å, R ₂ =?1.9527 Å ～?1.9851 Å at tetragonal site are obtained respectively, and the EPR and optical spectra agree well with the experimental results.     

Investigations on the local structure and EPR parameters for the trigonal Nd3+ centre in CdS

The local structure and the electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants) for the trigonal Nd³⁺ centre in CdS are theoretically investigated by considering the local lattice relaxation. The impurity Nd³⁺ is found not to occupy exactly the host Cd²⁺ site, but to suffer a shift of about 0.31 Å away from the sulphide triangle along the C₃ axis due to size and charge mismatch. The theoretical EPR parameters based on the above impurity axial displacement are in good agreement with the observed values. The local structure and the EPR parameters are discussed for this centre.     

Single crystal EPR spectrum of Cr3+ in lanthanum lutecium gallium garnet

The Cr³⁺ EPR spectra of YAG type crystals normally consist of four peaks whose positions are dependent on the axial zero-field splitting D with axis along a 111 direction and angle between that direction and the applied field H ₀. In LLGG only three principal peaks are observed with zero-field axis nearly along x, y or z. This anomaly is attributed to the relatively small size of Cr³⁺ compared to Lu³⁺ which it displaces in an octahedral site. D varies slightly for the different zero-field axes: 0.480 cm^–1 along x, 0.429 cm^–1 along y and 0.470 cm^–1 along z. The spectroscopic splitting factor g=1.978±0.001 is essentially isotropic and independent of axes within the experimental error.     

Local structure and the electron paramagnetic resonance parameters for the Cr3+ ions at K+-vacancy site in Cr3+:KZnF3 laser crystal

The quantitative relationship between the electron paramagnetic resonance (EPR) parameters D,g_∥,g_⊥ and the local structure parameters of Cr³⁺ ion in KZnF₃ crystals is established. The local structure for Cr³⁺ paramagnetic center in KZnF₃:Cr³⁺ crystal has been determined from EPR parameters of Cr³⁺ ion. This work shows that the trigonal crystal field of Cr³⁺ ion in KZnF₃ crystals comes from following two origins: (1) the nearest-neighbor K⁺ vacancy caused by the charge compensation in the [1 1 1]-axis direction; and (2) the lattice distortions of the nearest-neighbor fluorine coordination caused by the K⁺ vacancy and the differences in mass, charge, and radius between Cr³⁺ ion and Zn²⁺ ion. The unified calculation of the EPR zero-field splitting and g factors, taking into account the K⁺ vacancy and the lattice distortions, has been carried out on the basis of the complete diagonalization procedure and the superposition crystal-field model, all calculation results are in excellent agreement with the experimental data. Although the main source of the trigonal crystal field comes from the K⁺ vacancy caused by the charge compensation, the contribution of the lattice distortion cannot be neglected.     

Absorption and EPR spectra of Cr3+ ions in a LaBeAl11O19 crystal

Electron spectra of optical absorption and EPR of Cr³⁺ ions in a LaBeAl₁₁O₁₉ crystal are investigated. It is shown that the Cr³⁺ ions occupy, three different octahedral positions of Al³⁺ in the LaBeAl₁₁O₁₉ structure, namely, 12k, 2a, and 4f₂; the ratio of their intensitites is 1∶2∶30, respectively. Parameters of the Cr³⁺ centers are determined and its is shown that the optical absorption spectra in the visible region are practically determined by the Cr³⁺ (III) occupying the 4f₂-positions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 275–277, March–April, 1999.     

EPR parameters and defect structure of the tetrahedral Ti3+ defect center in beryl crystal

The EPR parameters (g factors g _i and hyperfine structure constants A _i , where i=x, y, z) of Ti³⁺ ion at the tetrahedral Si⁴⁺ site of beryl crystals are calculated within the rhombic symmetry approximation from the high-order perturbation formulas based on the two-spin-orbit (SO)-parameter model. In these formulas both the contribution due to the SO coupling parameter of the central 3d¹ ion and that of ligand ions are considered. From the calculations, the defect structure of the Ti³⁺ defect center in beryl crystal is estimated and the EPR parameters g _x , g _y , g _z and A _y are reasonably explained. The values of the parameters A _x and A _z (which were not reported) are suggested and remain to be checked by the further experimental studies.     

Theoretical investigation of the optical and EPR parameters for VOion in some complexes

The molecular orbital coefficients and the EPR parameters of trisodium citrate dihydrate, sodium hydrogen oxalate monohydrate, potassium d-gluconate monohydrate and L-Alanine vanadyl complexes are calculated theoretically. Two d-d transition spectra and EPR parameters for the VO²⁺ complex are calculated theoretically by using crystal-field theory. The calculated g and A paramaters have indicated that paramagnetic center is axially symmetric. Having the relations of g_∥〈g_⊥〈g_e and A_∥〉A_⊥ for VO²⁺ ions, it can be concluded that VO²⁺ ions are located in distorted octahedral sites (C_4v) elongated along the z-axis and the ground state of the paramagnetic electron is d_xy.     

Investigations of the local lattice distortions and the EPR parameters for the orthorhombic Pt3+ center in YAG

The local lattice distortions and the EPR parameters (anisotropic g factors and the hyperfine structure constants) for the orthorhombic Pt³⁺ center in YAG are theoretically investigated from the perturbation formulas of these parameters for a 5d⁷ ion in an orthorhombically elongated octahedron. The [ PtO₆] ^9- cluster on Al³⁺ site is found to experience the axial elongation of about 0.01 Å along Z axis, and the planar impurity-ligand bond lengths suffer the relative variation of about 0.11 Å? along X and Y axes due to the Jahn-Teller effect. As a result, the above local lattice distortions produce significant orthorhombic deformation, whereas the original slight trigonal distortion of the host [ AlO₆] ^9- octahedron is entirely depressed by the Jahn-Teller effect. The calculated EPR parameters based on the above lattice distortions show good agreement with the experimental data, and the local structure of the impurity center is also discussed.     

Al2O3:V3+晶体局域结构及其自旋哈密顿参量研究

提出了解释掺杂离子局域结构畸变的配体平面移动模型,建立了此模型下晶体微观结构与自旋哈密顿参量之间的定量关系.在考虑自旋与自旋、自旋与另一电子轨道和轨道与轨道作用等微小磁相互作用的基础上,采用全组态完全对角化方法,对Al2O3晶体中V3+的局域结构和自旋哈密顿参量进行了系统的研究.结果表明,V3+掺入Al2O3晶体后,上下配体氧平面间距离增大了0.0060 nm.从而成功地解释了Al2O3:V3+晶体的自旋哈密顿参量.在此基础上,研究了三角晶场下3d2离子自旋哈密顿参量的微观起源.研究发现,自旋三重态对自旋哈密顿参量的贡献是主要的,微小磁相互作用对自旋哈密顿参量的贡献只与自旋三重态有关.     

晶体CsMgCl3:Ni2+的局部结构、光谱和EPR谱的理论研究

本文采用半自洽场(semi-SCF) 自由Ni2+的3d轨道波函数、点电荷-偶极子模型和Ni2+-6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgCl3:Ni2+晶体的局部结构参数,统一解释了CsMgCl3:Ni2+晶体的吸收光谱和EPR 谱.此外,还讨论了高阶微扰方法、参量拟合方法等问题.理论计算结果与实验值符合得很好.     

Effect on the EPR and local lattice structure distortion of V3+ ion doping corundum crystal: three models studied

This paper reports on the application of conventional models (the displacement model and the elongation model) and the four-parameter model in detecting the local molecular structure of a coordination complex. By diagonalizing the complete energy matrices, the EPR parameters and optical spectra as well as the local distortion structure for V³⁺ ion in the Al₂O₃ : V³⁺ system have been studied using the three models. The four-parameter model is shown to provide a significant improvement over the conventional models. Based on these calculations, it was found that when V³⁺ is doped in Al₂O₃, the distance between upper and lower ligand oxygen plane increases by 0.16097 Å and the shifts of O^2? ions in the upper and lower ligand oxygen planes expand by 0.07076 Å and 0.004066 Å, respectively. To understand the detailed physical and chemical properties of the doped Al₂O₃, the contributions of the spin-orbit coupling to the zero-field splitting for V³⁺ ion are investigated.     

Covalent bonding and J–J mixing effects on the EPR parameters of Er~(3+) ions in GaN crystal

The EPR parameters of trivalent Er~(3+) ions doped in hexagonal Ga N crystal have been studied by diagonalizing the 364×364 complete energy matrices. The results indicate that the resonance ground states may be derived from the Kramers doublet Γ_6. The EPR g-factors may be ascribed to the stronger covalent bonding and nephelauxetic effects compared with other rare-earth doped complexes, as a result of the mismatch of ionic radii of the impurity Er~(3+)ion and the replaced Ga~(3+) ion apart from the intrinsic covalency of host Ga N. Furthermore, the J–J mixing effects on the EPR parameters from the high-lying manifolds have been evaluated. It is found that the dominant J–J mixing contribution is from the manifold ~2K_(15/2), which accounts for about 2.5%. The next important J–J contribution arises from the crystal–field mixture between the ground state ~4I_(15/2) and the first excited state~4I_(13/2), and is usually less than 0.2%. The contributions from the rest states may be ignored.     

Local structure distortion and spin Hamiltonian parameters for Cr3＋-Vzn tetragonal defect centre in Cr3＋ doped KZnF3 crystal

The quantitative relationship between the spin Hamiltonian parameters (D, g_‖, Δg) and the crystal structure parameters for the Cr³⁺—V_Zn tetragonal defect centre in a Cr³⁺:KZnF₃ crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr³⁺—V_Zn tetragonal defect centre in the KZnF_3 crystal are systematically investigated using the complete diagonalization method. It is found that the V_Zn vacancy and the differences in mass, radius and charge between the Cr³⁺ and the Zn²⁺ ions induce the local lattice distortion of the Cr³⁺ centre ions in the KZnF₃ crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Δg. We find that the ligand F^- ion along [001] and the other five F^- ions move towards the central Cr³⁺ by distances of Δ₁ = 0.0121 nm and Δ₂ = 0.0026 nm, respectively. Our approach takes into account the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It is found that for the Cr³⁺ ions in the Cr³⁺:KZnF₃ crystal, although the spin—orbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D.     

三角对称晶场中6 S(3d5)态离子零场分裂参量的微观起源

基于完全对角化方法(complete diagonalization method, CDM), 研究了⁶ S(3d⁵)态离子在三角晶场(包括C_3v,D₃,D_3d点群对称晶场)中零场分裂(zero-field splitting, ZFS)参量D和(a-F)的微观起源.研究中除了考虑研究者通常考虑的SO(spin-orbit)磁相互作用外,同 关键词： 6 S(3d⁵)态离子')" href="#">⁶ S(3d⁵)态离子 零场分裂参量 磁相互作用 完全对角化方法     

Local structure of the trigonal defect center for Cr3+ ions in KMgF3 crystals

Abstract

The zero-field splitting D, the anisotropic g-factors g _∥, Δg(=g _∥ ? g _⊥) and the first excited state splitting Δ(² E) for the trigonal Cr³⁺–V_K center in KMgF₃: Cr³⁺ crystals have been studied from Macfarlane's high-order perturbation formulas. From the studies, the local structure of the trigonal center is obtained. The local lattice distortions (i.e., the displacement directions of the ions in the center) are consistent with the expectation based on the electrostatic interaction.     

Theoretical studies on the EPR parameters of the interstitial V4+ in rutile

The electron paramagnetic resonance (EPR) parameters g-factors g _i (i=x, y, z) and the hyperfine structure constants A _i for the interstitial V⁴⁺ in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d¹ ion in rhombically distorted octahedra. On the basis of the studies, the local axial distortion angle Δα′ in the impurity center is found to be about 2° smaller than the host value, characterized as stretching and contraction of the parallel and perpendicular bonding lengths by about 0.28 and 0.14 Å,respectively. This results in the less compressed ligand octahedron because of the Jahn–Teller effect and space effect arising from occupation of the impurity V⁴⁺ at the interstitial site. The theoretical EPR parameters based on the above local structural parameters of this work are in better agreement with the experimental data than those of the previous studies in the absence of the local angular distortion and the ligand orbital contributions. The two experimental optical absorption bands are also reasonably analyzed.