共查询到20条相似文献,搜索用时 31 毫秒
1.
Souha Kammoun Hajer Souissi Ramzi Maalej Mohamed Dammak Mohamed Kamoun 《Journal of luminescence》2009,129(5):411-415
The experimental studies have provided evidence of the occurrence of transitions from the 3T1g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3P) and 3A2g(3F) for the V3+ centres in Al2O3 crystal; and from the 3A2g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3F) and 3T1g(3P) for the Ni2+ centres in LiNbO3 crystal (levels are assigned to irreps of the Oh point symmetry group). Using the experimental spectroscopic data, theoretical calculations of the crystal-field levels of V3+:Al2O3 and Ni2+:LiNbO3 are carried out based on the Racah theory. The observed crystalline-field splittings of the V3+ and Ni2+ terms were accounted for using a C3 symmetry Hamiltonian. The spin-orbit interaction was taken into account in this work. The Racah, crystal-field and spin-orbit parameters, which fit experimental and theoretical energy levels, have been reliably obtained. A good agreement between the theoretical and experimental results for the energy levels of V3+:Al2O3 and Ni2+:LiNbO3 has been obtained. 相似文献
2.
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
3.
The local structure and the g factor (gx, gy, and gz) of the Ni+ center in KTaO3 are theoretically studied using the perturbation formulas of the g factors for a 3d9 ion in orthorhombically elongated octahedra. The orthorhombic field parameters are determined from the superposition model and the local geometry of the system. In view of the covalency, the contributions from the ligand orbital and spin–orbit coupling interactions are taken into account from the cluster approach. In the calculations, the orthorhombic center is attributed to Ni+ occupying the host Ta5+ site, associated with the nearest-neighboring oxygen vacancy VO along the c-axis. Furthermore, the planar Ni+–O2− bonds are found to experience the relative variation ΔR (≈0.076 Å) along the a- and b-axis, respectively, due to the Jahn–Teller effect and the size mismatching substitution of Ta5+ by Ni+. Meanwhile, the effectively positive VO can make the central Ni+ displace away from VO along the c-axis by about 0.20 Å. The calculated g factors based on the above local distortions show good agreement with the experimental data. 相似文献
4.
The optical absorption spectrum, zero-field splitting (ZFS) and EPR g factor of LiNbO3:Ni2+ are explained uniformly on the basis of complete energy matrix diagonalization procedure (CDP) and Zhao's self-consistent field (SCF) d-orbit of free Ni2+ ions. The agreement between the calculated results and the experimental data shows quantitatively that impurities Ni2+ replace the Nb5+ rather than Li+ sites in LiNbO3:Ni2+. 相似文献
5.
The electron paramagnetic resonance g factors and the local structure for Ni3+ in LaAl0.9Ni0.1O3 (LAN), La0.75Y0.25Al0.99Ni0.01O3 (LYAN) and YAl0.9Ni0.1O3 (YAN) are theoretically studied from the perturbation formulas of the g factors for a 3d7 ion of low spin (S = 1/2) in tetragonally elongated octahedra. In these formulas, the contributions to the g factors from the tetragonal distortion, characterized by the tetragonal field parameters Ds and Dt are taken into account. According to the calculations, the ligand octahedra around Ni3+ are suggested to suffer 2% relative elongation along the [001] (or C4) axis due to the Jahn-Teller effect. 相似文献
6.
By analyzing the EPR spectrum of transition-metal ion Fe3+ in Al2O3:Fe3+ system, the local lattice structure around impurity Fe3+ ion in the crystal has been studied by means of the diagonalization of the 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 two three-edge-pyramids elongated obviously along C3 axis. The two distortion angles Δθ1=−1.1±0.1°,Δθ2=−1.8° as well as the two Fe-O bond lengths R1=2.016 A, R2=1.907 A are determined, respectively. 相似文献
7.
An analysis of the relationship between the EPR trigonal-field parameters and the local crystal structure of KZnF3:Fe3+system is presented by diagonalizing the complete energy matrices for a d5 configuration ion in a trigonal crystal field. We propose a two-layer-ligand model, in which the ligands consist of six nearest-neighbor F− ions in the first layer and eight next nearest-neighbor K+ ions in the second layer. The calculation indicates that the local structure distortion of KZnF3:Fe3+system is due to the displacement of a K+ ion along C3 axis towards the Fe3+ ion, which leads to the shift of the F− ions away from C3 axis. By simulating the EPR low-symmetry parameters D and (a−F), the distorted angles between the Fe3+-F− bonds and C3 axis are determined, Δθ1=2.58°, Δθ2=−1.4° at room temperature (300 K) and Δθ1=2.84°, Δθ2=−1.4° at low temperature (77 K). Those results are in good agreement with the experimental findings Δθ1=2.8±0.3°and Δθ2=−1.1±0.3°. 相似文献
8.
W.L. Feng X.M. Li W.C. Zheng Y.G. YangW.Q. Yang 《Journal of magnetism and magnetic materials》2011,323(5):528-531
The EPR g factors, g|| and g⊥, for the isoelectronic 3d9 ions Ni+ and Cu2+ at the tetragonal Cu+ site of the CuGaSe2 crystal are calculated from the high-order perturbation formulas based on a two-spin-orbit-parameter model. In the model, both the contributions to g factors from the spin-orbit parameter of central 3d9 ion and that of ligand ion are contained. The calculated results appear to be consistent with the experimental values. The tetragonal distortions (characterized by θ−θ0, where θ is the angle between the metal-ligand bond and C4 axis, and θ0≈54.74° is the same angle in cubic symmetry) of Ni+ and Cu2+ centers, which are different from the corresponding angle in the host CuGaSe2 crystal and from impurity to impurity, are obtained from the calculations. The difference of the sign of g||−g⊥ between the isoelectronic Ni+ and Cu2+ centers is found to be due to the different tetragonal distortions of both centers in the CuGaSe2 crystal. 相似文献
9.
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
10.
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
11.
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
12.
V. G. Babajanyan R. B. Kostanyan P. H. Muzhikyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2012,47(1):17-22
The results of investigations of luminescent radiations’ kinetic characteristics for LiNbO3:Yb3+-Er3+, LiNbO3:Er3+, and LiNbO3:Yb3+ crystals under optical excitations at 532 nm and 1064 nm wavelengths are presented. The shapes and times of rise and damping
of luminescent signals at 550 nm, 980 nm and 1555 nm wavelengths under selective excitations in the impurity subsystem of
the investigated materials are determined. Comparison of the temporal characteristics of luminescent responses of LiNbO3 crystals doped separately with Yb3+ and Er3+ ions with those of the LiNbO3:Yb3+-Er3+ crystal allows identifying the contributions from different energy transfer processes of optical excitation taking place
in the impurity subsystem of the material. 相似文献
13.
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
14.
Czeslaw Rudowicz Zi-Yuan Yang Jian Qin 《Journal of Physics and Chemistry of Solids》2003,64(8):1419-1428
A new module has been developed within the CFA/MSH computer package, which is applicable for d2 and d8 ions at sites of trigonal symmetry type I (C3v,D3,D3d) and type II (C3,C3i), including the ‘imaginary’ CF term. For the first time the spin-spin (SS) and spin-other-orbit (SOO) interactions have also been included in the Hamiltonian. This module enables to study the contributions to the energy levels and the spin Hamiltonian parameters, i.e. zero-field splitting D and g-factors: g∥ and g⊥. The contributions arising from the spin-orbit (SO), SS, and SOO interaction as well as those due to the low symmetry CF effects induced by the distortion angle ?, which describes the difference between C3 and C3v symmetry, can be studied. As an application of the new module, calculations have been carried out for V3+(3d2) ions in α-Al2O3 crystal, taking into account for the first time the SS and SOO interactions, and the low symmetry CF effects. The results show that (i) the contributions from the SS and SOO interactions to the energy levels are larger for free V3+ ions than those for V3+ ions in α-Al2O3 crystal, (ii) both the contributions to the SH parameters and the energy levels arising from the SOO interaction are larger than those arising from the SS interaction, (iii) the contributions due to the low symmetry CF effects induced by the distortion angle ? are in general significant, (iv) D and g⊥ are sensitive to the distortion angle ?, whereas g∥ is insensitive to ?, and (v) the influence of the lattice distortions on the spectroscopic properties of V3+ ion in α-Al2O3 is pronounced. It appears important for similar ion-crystal cases to consider the lattice distortions in detailed calculations, which take into account the relevant contributions from the SO, SS and SOO interactions. A good agreement between the theoretical and experimental results has been obtained. 相似文献
15.
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 O2? 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. 相似文献
16.
Chengkang Chang Wen Li Xiaojun Huang Zhiyu Wang Xi Chen Xi Qian Rui Guo Yuelei Ding Dali Mao 《Journal of luminescence》2010,130(3):347-350
This paper reports the photoluminescence and afterglow behavior of Eu2+ and Eu3+ in Sr3Al2O6 matrix co-doped with Dy3+. The samples containing Eu2+ and Eu3+ were prepared via solid-state reaction. X-ray diffraction (XRD), photo luminescent spectroscope (PLS) and thermal luminescent spectroscope (TLS) were employed to characterize the phosphors. The comparison between the emission spectra revealed that Sr3Al2O6 phosphors doped with Eu2+, Dy3+ and Eu3+, Dy3+ showed different photoluminescence. The phosphor doped with Eu3+, Dy3+ showed an intrinsic f-f transition generated from Eu3+, with two significant emissions at 591 and 610 nm. However, the phosphor doped with Eu2+, Dy3+ revealed a broad d-f emission centering around 512 nm. After the UV source was turned off, Eu2+, Dy3+ activated Sr3Al2O6 phosphor showed excellent afterglow while Eu3+, Dy3+ activated phosphor almost showed no afterglow. Thermal simulated luminescence study indicated that the persistent afterglow of Sr3Al2O6: Eu2+, Dy3+ phosphor was generated by suitable electron traps formed by the co-doped rare-earth ions (Dy3+) within the host. 相似文献
17.
Antiferromagnetic phase transition in two vanadium garnets AgCa2Co2V3O12 and AgCa2Ni2V3O12 has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature TN=6.39 K for AgCa2Co2V3O12 and 7.21 K for AgCa2Ni2V3O12, respectively. The magnetic susceptibilities exhibit broad maximum, and these TN correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χmax). The magnetic entropy changes from zero to 20 K per mol Co2+ and Ni2+ ions are 5.31 J K−1 mol-Co2+-ion−1 and 6.85 J K−1 mol-Ni2+-ion−1, indicating S=1/2 for Co2+ ion and S=1 for Ni2+ ion. The magnetic susceptibility of AgCa2Ni2V3O12 shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μeff=3.23 μB Ni2+-ion−1 and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa2Co2V3O12. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state 2E(t26e) and the first excited state is spin quartet state 4T1(t25e2) which locates extremely close to the ground state. The low spin state S=1/2 for Co2+ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity. 相似文献
18.
研究了通过有机金属化学气相沉积技术及单源分子前躯体方法制备的Ni/Al2O3纳米复合材料的氢吸附(存储). 在冷壁的有机金属化学气相沉积反应器中,通过降解Ni(acac)2粉末基底上的[H2Al(OtBu)]2制备的Ni/Al2O3纳米复合材料. 通过X射线粉末衍射、扫描电镜、透射电镜以及能量色散型X射线荧光光谱等技术表征该复合材料. 采用自制Sievert's设备研究该复合材料的氢吸附(存储),可以储存约2.9%(重量比)的氢. 相似文献
19.
A theoretical method for studying the inter-relation between electron and molecule structure is proposed on the basis of the complete energy matrices of the electron-electron repulsion, the ligand-field and the spin-orbit coupling for d5 configuration ion in a trigonal ligand-field. As an application, the local distortion structure of (FeCl6)3- coordination complex for Fe3+ ions doped into CdCl2 is investigated. Both the second-order zero-field splitting parameter and fourth-order zero-field splitting parameter are considered simultaneously in the structural investigation. By diagonalizing the complete energy matrices, the local structure distortion parameters ΔR=−0.24 Å, Δθ=2.137° at 26 K and ΔR=−0.203 Å, Δθ=2.515° at 225 K for Fe3+ ions in CdCl2 are determined. These results elucidate a microscopic origin of various ligand-field parameters which are usually used empirically for the interpretation of electron paramagnetic resonance results. It is found that the theoretical results are in good agreement with the experimental values. 相似文献
20.
By employing the perturbation formulae of the spin Hamiltonian parameters (SHPs) (g factors gxx, gyy, gzz, hyperfine structure constants Axx, Ayy, Azz and superhyperfine parameters Axx׳, Ayy׳, Azz׳) for a 3d1 ion in orthorhombically elongated octahedra and tetrahedra, the defect structures and the experimental EPR spectra are theoretically and systematically investigated for the two orthorhombic Ti3+ centers C1 and C2 in ZnWO4. Center C1 is ascribed to the impurity Ti3+ at host W6+ site associated with two nearest neighbor oxygen vacancies due to charge compensation. The resultant tetrahedral [TiO4]5– cluster is determined to undergo the local orthorhombic elongation distortion, characterized by the axial distortion angle Δθ (=θ–θ0≈–6.84°) of the local impurity-ligand bond angle θ related to θ0 (≈54.74°) and the perpendicular distortion angle Δε (=ε–ε0≈2.5°) related to ε0 (≈45°) of an ideal tetrahedron because of the Jahn–Teller effect. Center C2 is attributed to Ti3+ on Zn2+ site, and this octahedral [TiO6]9– cluster may experience the local axial elongation ΔZ (≈0.001 Ǻ) and the planar bond angle variation Δφ (≈9.1°) due to the Jahn–Teller effect, resulting in a more regular oxygen octahedron. All the calculated SHPs (i.e., g factors for both centers, the hyperfine structure constants for center C2 and superhyperfine parameters of next nearest neighbor ligand W for center C1) show good agreement with the observed values. However, the theoretical results based on the previous assignment of center C1 as Ti3+ on W6+ site with only one nearest planar oxygen vacancy (i.e., five-fold coordinated octahedral [TiO5]7– cluster) show much worse agreement with the experimental data. The defect structures and the SHPs (especially the g anisotropies) are discussed for both centers. The present studies on the superhyperfine parameters of ligand W6+ for center C1 would be helpful to further investigations on the superhyperfine interactions of cation ligands which were rather scarcely treated before. 相似文献