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1.
M.G. Brik 《Journal of Physics and Chemistry of Solids》2006,67(7):1599-1604
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. 相似文献
2.
Absorption and emission spectra of dysprosiumaluminumgarnet (pure and diluted with yttrium) and of dysprosiumgalliumgarnet (pure and diluted with yttrium) have been observed in the infrared and visible spectral region. The crystal field levels of the6H and the6F multiplets have been deduced in both garnet systems. For the crystal field levels of the gallium-garnet a crystal field calculation is performed in a pseudocubic approximation. 相似文献
3.
4.
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. 相似文献
5.
A detailed analysis of the energy level structure of the six-fold coordinated Cr3+ ion in the chromium oxide Cr2O3 is performed using the exchange charge model of the crystal field theory. Parameters of the crystal field acting on the Cr3+ optical electrons are calculated from the crystal structure data for the [CrO6]9− impurity center. The energy levels obtained are compared with the experimental absorption spectra for the considered crystal; a good agreement with experimental data is demonstrated. One possible explanation for the ultraviolet p1 absorption band is proposed based on the results of crystal field calculations. 相似文献
6.
The effective operators of the spin correlated crystal field have been formed by coupling the exchange with the crystal field. The exchange field is a scalar in spin space so the effective operators will still have the same rank as that of the crystal field but will give non-zero matrix elements between the states 2S+1LJ of the half filled shells, contrary to the zero value obtained for a pure crystal field tensor. 相似文献
7.
P. Dorenbos 《Journal of luminescence》2002,99(3):283-299
Information on the energy of 5d-levels of Ce3+ ions in aluminates and “simple” oxides has been collected. The crystal field splitting of the 5d-levels is interpreted in terms of the type and size of anion polyhedron coordinating the Ce3+ ion. The centroid (barycenter) shift of the 5d-configuration is analyzed by a ligand polarization model providing values for the spectroscopic polarizability αsp of the anion ligands. The data provide evidence that the centroid shift behaves independently from the crystal field splitting. By combining centroid shift and crystal field splitting, the “spectroscopic” redshift of the first electric dipole-allowed fd transition of Ce3+-doped in the compounds will be interpreted. The large crystal field splitting in garnet compounds and the small splitting in perovskite compounds will be discussed. 相似文献
8.
H. Kubota K. Matsuta Y. Nojiri T. Minamisono N. Itoh T. Kawabata S. Koike 《Hyperfine Interactions》1987,35(1-4):605-608
Nuclear quadrupole effects in the NMR spectra of12N implanted in GaN crystal was studied. Broad quadrupole spectra were observed almost independent of the crystal orientation
relative to the external magnetic field. Homogeneously oriented field gradients distributed in the range 0<⋎eqQ/h⋎<400 kHz
were consistent with in vacancies and/or 0 impurities of densities 1019/cc in the GaN crystal. 相似文献
9.
M. L. Falin K. I. Gerasimov V. A. Latypov A. M. Leushin A. Hoefstaetter 《Applied magnetic resonance》2011,40(1):65-73
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. 相似文献
10.
Radenka M. Krsmanovi? ?eljka Anti? Miodrag Mitri? Miroslav D. Drami?anin Mikhail G. Brik 《Applied Physics A: Materials Science & Processing》2011,104(1):483-492
In this paper we presented structural and spectroscopic study of zinc silicate powder samples doped with divalent nickel and cobalt ions. Results of the Rietveld structural refinement, combined with optical spectroscopic study and theoretical crystal field calculations, are presented and discussed. X-ray diffraction studies were performed to establish reliable structure of the doped samples; in this way the interionic distances and chemical bond angles in Zn2SiO4:Co2+ and Zn2SiO4:Ni2+ were calculated and are reported for the first time. The room temperature reflection spectra of the prepared samples were measured in a spectral region from 4000 to 50000 cm?1. The exchange charge model of crystal field has been applied to analyze the experimental spectra and assign all observed details in the spectra to the corresponding electronic transitions between the Co2+ and Ni2+ crystal field energy levels. The only input information for the model calculation was the experimentally obtained structural data, which were used for the calculations of the crystal field parameters with subsequent diagonalization of the crystal field Hamiltonian for both ions. Agreement between the calculated and experimentally detected energy levels of impurity ions was good. On the basis of the crystallographic and crystal field studies it was established that there exists a systematic trend of preferential occupation of one out of two possible crystallographic sites (namely, Zn2) for both impurity ions. 相似文献
11.
Mikhail G. Brik Nicolae M. Avram Calin N. Avram 《Central European Journal of Physics》2005,3(4):508-524
The exchange charge model of crystal field theory has been used to analyze the ground and excited state absorption of tetrahedrally coordinated Cr4+ ion in lithium aluminum oxide LiAlO2 (γ-phase) and lithium dioxogallate LiGaO2. The parameters of the crystal field acting on the Cr4+ ion are calculated from the crystal structure data, taking into account the crystal lattice ions located at distances up to 12.744 Å in LiGaO2 and 13. 180 Å in LiAlO2. The obtained energy level schemes were compared with experimental ground and excited state absorption spectra and literature data on the application of other crystal field models (the angular overlap model and Racah theory) to the considered crystals; a good agreement with experimental data is demonstrated. 相似文献
12.
Zero-field splitting and g-anisotropy of the ground multiplet of HfS2(V2+) have been measured by electron paramagnetic resonance. The unusually large g-anisotropy and its relationship to the zero-field splitting alow a comparison between various crystal field theories. We find that the experimental results are in disagreement with the simple crystal field theory of Van Vleck for the ground multiplet of d3 ions in trigonally distroted octahedral environments, but in reasonable agreement with the more elaborate but straightforward crystal field theory of Macfarlane. We thus conclude that it is unnecessary to resort to an anisotropic spin-orbit coupling as suggested by Sugano and Tanabe or to odd-parity crystal field terms as suggested by Artman and Murphy. 相似文献
13.
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 相似文献
14.
Method for fitting crystal field parameters and the energy level fitting for Yb3+ in crystal Sc2O3 下载免费PDF全文
<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. 相似文献
15.
Forbidden ESR transitions were investigated at 9 GHz in zinc oxide doped with Fe3+ and Mn2+. The crystal field parameters were determined by means of a computer program. Furtheron, the splittings of the lines for general orientations of the crystal axes relative to the magnetic field were calculated. 相似文献
16.
R.A.B. Devine 《Solid State Communications》1973,13(7):935-938
A recent interpretation of the crystal field ground state of Dy3+ in Pd is discussed in terms of a model where isotropic conduction electron/ion exchange is included. The new results suggest the ratio of fourth and sixth order crystal field parameters to be 292±4. The magnitude of the crystal field parameters cannot be determined. A resonance originating possibly from Dy ions in non-cubic sites is identified. 相似文献
17.
Influence of impurity Ni2+ ions on optical absorption spectra of layered CdI2 single crystals has been considered for localized level of doping. Optical properties of CdI2:Ni2+ crystals were modeled using two independent approaches: (i) DFT-based ab initio calculations and (ii) semi-empirical crystal field theory. The former method allowed for locating the Ni2+ 3d states with respect to the host’s band structure, providing a link between the properties of impurity and host itself. The latter method allowed for calculations of crystal field splitting of the Ni2+ LS terms, giving an opportunity to assign the main bands in the absorption spectrum of the doped crystal. To increase accuracy in calculating the point charge contribution to the crystal field parameters (CFP), contributions of all crystal lattice ions located at a distance of up to 72.999 Å from the Ni ion were included into the crystal lattice sums. The crystal field Hamiltonian was diagonalized in the space of 25 wave functions of the spin-triplet terms 3F, 3P and the spin-singlet terms 1S, 1D, 1G of the 3d8 electron configuration of Ni2+ ion. Additional calculations of the band structure and optical functions were performed to reveal the structure of the energy bands, their role in the formation of optical properties of this system in the overlapping impurity-ligand effects. Electron density distribution in the space between atoms before and after doping was compared; hybridization of the Ni 3d states with iodine 5p states was demonstrated. The role of the crystal anisotropy in the observed effects is discussed. 相似文献
18.
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. 相似文献
19.
R. Chamard-Bois J. Rossat-Mignod K. Knorr W. Drexel 《Solid State Communications》1973,13(10):1549-1553
Inelastic neutron time of flight measurements have been carried out on the intermetallic compound HoRh at different temperatures. Well resolved transitions between crystal field levels were observed at 4.0 and 9.7 meV. The complete crystal field level scheme was deduced and the crystal field parameters were found to be A40 〈r4〉 = ?10.98 meV and A60 〈r6〉 = ?1.59 meV. These values deviate considerably from point charge estimates. 相似文献