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1.
《Journal of magnetism and magnetic materials》2002,238(2-3):200-206
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. 相似文献
2.
The formulas of the crystal-field theory have been adapted to a system with the symmetry group C
3v. A simple method has been proposed for including the polarization of the local environment of the Cr3+ impurity ion in LiNbO3. A model dependent on one parameter has been proposed for a distortion of the niobium octahedron due to the incorporation
of the trivalent chromium ion. This parameter has been determined from experimental data. The parameters of the intraionic
and interionic interactions have been obtained for the Cr3+ ion in the lithium and niobium positions of the crystal lattice of lithium niobate. 相似文献
3.
Local structure distortion and spin Hamiltonian parameters for Cr3+-Vzn tetragonal defect centre in Cr3+ doped KZnF3 crystal
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The quantitative relationship between the spin Hamiltonian parameters (D, g‖, Δg) and the crystal structure parameters for the Cr3+—VZn 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+—VZn tetragonal defect centre in the KZnF_3 crystal are systematically investigated using the complete diagonalization method. It is found that the VZn 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. 相似文献
4.
Ai-Jie Mao 《Molecular physics》2013,111(8):1033-1038
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. 相似文献
5.
By analyzing the EPR parameters a, D and F of Cr2+ ion located at tetrahedral site in ZnS, the local structure around Cr2+ in the crystal has been investigated on the basis of the complete energy matrix for a d4 configuration in a tetragonal ligand-field within a strong-field-representation. It is shown that there exists an expansion distortion in the local lattice structure. From EPR calculation, the distortion parameters ΔR=0.13 Å and Δθ=1.417° are determined. 相似文献
6.
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. 相似文献
7.
The formulas of crystal field theory are derived for a particular case of the C
3v
symmetry group. Convenient and numerically simple methods are proposed to take into account the polarization of the local
environment of the Cr3+ impurity ion in LiNbO3. The parameters of intraion interactions for Cr3+ in lithium and niobium positions in the lithium niobate lattice and the distortion of the niobium octahedron in lithium niobate,
which is caused by the incorporation of trivalent chromium ion, are determined. 相似文献
8.
Yang Zi-Yuan 《Physica B: Condensed Matter》2011,406(20):3975-3979
The local structure distortion and the spin Hamiltonian (SH) parameters, including the zero-field splitting (ZFS) parameter D and the Zeeman g-factors g‖ and g⊥, are theoretically investigated by means of complete diagonalization method (CDM) and the microscopic spin Hamiltonian theory for tetragonal charge compensation CrF5O defect center in Cr3+:KMgF3 crystals. The superposition model (SPM) calculations are carried out to provide the crystal field (CF) parameters. This investigation reveals that the replacement of O2− for F− and its induced lattice relaxation Δ1(O2−) combined with an inward relaxation of the nearest five fluorine Δ2(F−) give rise to a strong tetragonal crystal field, which in turn results in the large ZFS and large anisotropic g-factor Δg. The experimental SH parameters D and Δg can be reproduced well by assuming that O2− moves towards the central ion Cr3+ by Δ1(O2−)=0.172R0 and the five F− ions towards the central ion Cr3+ by Δ2(F−)=0.022R0. Our approach takes into account the spin-orbit (SO) interaction as well as the spin-spin (SS), spin-other-orbit (SOO), and orbit-orbit (OO) interactions omitted in previous studies. This shows that although the SO interaction is the most important one, the contributions to the SH parameters from other three magnetic interactions are appreciable and should not be omitted, especially for the ZFS parameter D. 相似文献
9.
The complete diagonalisation (of energy matrix) method is applied in this paper to calculate together the optical and electron paramagnetic resonance (EPR) spectral data for Cr3+ ion at the trigonal Ga3+ site of Y3Ga5O12 crystal. The method is founded on the two-spin-orbit-parameter model where in addition to the contributions from the spin-orbit parameter of central dn ion (i.e., one-spin-orbit-parameter model) in the traditional crystal field theory, those from the spin-orbit parameter of ligand ion via covalence effect is also considered. The calculated results propose that by using only four adjustable parameters, the 12 observed spectral data (nine optical band positions and three EPR parameters g//, g⊥ and D) in Y3Ga5O12: Cr3+ are reasonably explained. The impurity-induced local lattice distortion of Cr3+ in Y3Ga5O12 crystal is also estimated through the calculations. The results are discussed. 相似文献
10.
E. A. Vinogradov B. N. Mavrin N. N. Novikova V. A. Yakovlev D. M. Popova 《Laser Physics》2009,19(2):162-170
Recently ultrabroadband infrared solid state lasers based on a new vibronic material Cr2+:ZnSe x S1–x were demonstrated [1–3]. Cr2+ ion substitutes the metal ion (tetrahedral sites), the crystal field of the solid solution is responsible for large inhomogeneous broadening of Cr2+ electron states. The crystal field can be reconstructed by investigation of lattice dynamics — optical phonon parameters and dielectric function in IR. We paid special attention to investigation of vibrational and infrared spectroscopic properties of ZnSe x S1 ? x crystals. A very interesting and somewhat unexpected result of these studies was the existence in the crystals of effective S-Se dipoles, which generate an additional deep dynamically charged level in the forbidden gap of the semiconductors. The results of the first-principles calculations of both the phonon structure and the electron localization in ZnSe x S1–x crystals as well as acceptor levels in Cr2+: ZnSe crystal are discussed. 相似文献
11.
On the basis of the 120×120 complete energy matrices for a d3 configuration ion in a trigonal ligand field, for Cr3+ ions doped in MgTiO3 and LiTaO3, the local structures and EPR g factors of the octahedral (CrO6)9− clusters have been studied, respectively. By simulating the calculated optical spectra and the EPR spectra data to the experimental results, local structure parameters are obtained. The calculated results show that although the local lattice structures around the M (M=Mg2+, Ta5+) ions are obviously different, after Cr3+ replacing the M, the local lattice structures around the Cr3+ ions are quite similar and close to those of the Cr2O3. This may be ascribed to the fact that the octahedral Cr3+ center in MgTiO3:Cr3+ and LiTaO3:Cr3+ systems and that in Cr2O3 exhibit similar octahedral (CrO6)9− clusters. Moreover, the corresponding theoretical values of the optical spectra have been reported. It is also found that the orbital reduction factor k is very important to understand the EPR g factors for Cr3+ ions doped in MgTiO3 and LiTaO3. 相似文献
12.
A single-crystal TlGaSe2 doped by paramagnetic Fe ions has been studied at room temperature by electron paramagnetic resonance (EPR) technique. The fine structure of EPR spectra of paramagnetic Fe3+ ions was observed. The spectra were interpreted to correspond to the transitions among spin multiplet (S=5/2, L=0) of Fe3+ ion, which are splitted by the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe3+ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe3+ site and CF parameters were determined. Experimental results indicate that the Fe ions substitute Ga at the center of GaSe4 tetrahedrons, and the rhombic distortion of the CF is caused by the Tl ions located in the trigonal cavities between the tetrahedral complexes. 相似文献
13.
14.
Cheng-Gang Li Mei-Ling Duan Ya-Ru Zhao 《Journal of Physics and Chemistry of Solids》2010,71(11):1599-1602
The local lattice structure and EPR parameters (D, g‖, g⊥) have been studied systematically on the basis of the complete energy matrix for a d3 configuration ion in a trigonal ligand field. By simulating the calculated optical and EPR spectra data to the experimental results, the local distortion parameters (ΔR, Δθ) are determined for V2+ ions in CdCl2 and CsMgCl3 crystals, respectively. The results show that the local lattice structure of CdCl2:V2+ system exhibits a compression distortion (ΔR=−0.0868 Å) while that of CsMgCl3:V2+ system exists an elongation distortion (ΔR=0.0165 Å). The different distortion may be ascribed to the fact that the radius of V2+ ion is smaller than that of Cd2+ ion or larger than that of Mg2+ ion. Moreover, the relationships between EPR parameter D and local structure parameters (R, θ) as well as the orbital reduction factor k and g‐factors (g‖, g⊥) are discussed. 相似文献
15.
By analyzing the EPR spectra of Fe3+ ion in the fluorinde glasses, the local lattice structures around impurity Fe3+ ion in MF3:Fe3+ (M=Al, Ga) systems have been studied by means of diagonalizing the complete energy matrices of the electron-electron repulsion, the ligand-field and the spin-orbit coupling for a d5 configuration ion in a trigonal ligand-field. Both the second-order and fourth-order EPR parameters D and (a−F) are taken simultaneously in the structural investigation. The results indicate that the local lattice structure around octahedral Fe3+ center has an expansion distortion for Fe3+ in MF3:Fe3+ (M=Al, Ga). The expansion distortion may be ascribed to the fact that the radius of Fe3+ ion is larger than that of Al3+ ion and Ga3+ ion, and the Fe3+ ion will push the fluoride ligands upwards and downwards, respectively. The local lattice structure parameters R=1.927 A, θ=55.538° for Fe3+ in AlF3:Fe3+ and R=1.931 A, θ=56.09° for Fe3+ in GaF3:Fe3+ are determined, respectively, and the EPR spectra of the MF3:Fe3+ (M=Al, Ga) systems are satisfactorily explained. 相似文献
16.
17.
应用晶体场理论和不可约张量算符方法构造了3d2/3d8态离子在C3v对称晶场中包含自旋-轨道相互作用、自旋-自旋相互作用、自旋-其它轨道相互作用和其它轨道-其它轨道相互作用四种微观磁效应的45阶可完全对角化的能量哈密顿矩阵.利用该矩阵,计算了V3+∶α-Al2O3和Ni2+∶α-Al2O3晶体的光谱精细结构、晶体局域结构和零场分裂参量,研究了掺入两种互补态离子Ni2+和V3+对同种晶体的光谱精细结构、晶体局域结构和零场分裂参量的影响,理论计算值和实验值相符.研究发现:掺杂没有改变晶体的光谱精细结构和能级分裂条数,但改变了能级间距|掺杂也没有改变晶体的对称性,但使晶体局域结构发生了一定程度的畸变| Ni2+∶α-Al2O3晶体局域结构的伸长畸变量大于V3+∶α-Al2O3晶体,键角的变化量小于V3+∶α-Al2O3晶体. 相似文献
18.
The presence of Fe3+ centers with trigonal symmetry in chlorinated SrCl2 crystal is an interesting phenomenon. By diagonalizing the complete energy matrices for a d5 configuration ion in a trigonal ligand-field and simulating the EPR low-symmetry parameters D and (a−F) simultaneously, the local lattice structure around trigonal Fe3+ center in SrCl2:Fe3+ system has been studied. It is shown that Nistor et al.'s viewpoint about replacement is right, but the Cl− ion along 〈111〉 axis around the Fe3+ center is replaced not by an O2− ion but by some negative ion with effective charge to be less than that of Cl− ion. Our results indicate that when the ratio of the effective charge of the negative ion to that of Cl− ion is 0.8 as well as the distortion angle of the upper triangle is Δθ=−4.682°, the EPR parameters D and (a−F) can be explained satisfactorily. 相似文献
19.
Z. -Y. Yang 《Applied magnetic resonance》2000,18(4):455-461
In this paper, the electron paramagnetic resonance (EPR) parameters in RbCdF3:Cr3+ have been studied by means of energy matrices and the Newman superposition model, the theoretical results are in excellent agreement with the experimental ones. The existence of Rb+ vacancy and the lattice distortion have been verified. The EPR parameters arising from the Rb+ vacancy itself and the crystal lattice distortion are analyzed and calculated. We obtain that the six ligand F− ions move to the central Cr3+ ion by Δ = 0.0013 nm, and the front three F− ions rotate 2.98° away from the [111] axis while the back three F− ions rotate 1.016° toward it. 相似文献
20.
E. Cavalli 《Journal of Physics and Chemistry of Solids》2008,69(1):29-34
Single crystals of MWO4 (M=Mg, Zn, Cd) and MgMoO4 doped with Cr3+ have been grown by the flux growth method. Their optical spectra have been systematically measured and assigned on the basis of the classical Ligand Field Theory. The exchange charge model of the crystal field has then been applied to calculate the crystal field parameters (CFPs) and the energy levels of the Cr3+ ion in all studied crystals. These are in reasonable agreement with the experimental data. Systematic trends in the CFPs values, crystal field splittings and Racah parameters have been evidenced and their relation with sizes and symmetry properties of the host cavities occupied by Cr3+ has been pointed out. 相似文献