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1.
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   

2.
The parameters of the crystal field of the tetragonal oxygen center associated with a Yb3+ ion in the KMgF3 crystal found previously in a study of optical and ESR spectra are applied to analyze lattice distortions in the vicinity of the impurity ion and the O2? ion compensating for the excess positive charge. Within the superposition model, it was ascertained that the Yb3+ ion and the neighboring ions of fluorine and oxygen on the axis of the center shift significantly along the direction from the O2? ion to the Yb3+ ion during the formation of the tetragonal oxygen center. As this takes place, the distances of both (fluorine and oxygen) ions from the impurity ion increase. The four F? ions of the nearest octahedral neighborhood of Yb3+ that are arranged symmetrically in the plane perpendicular to the axis of the center slightly recede from the axis.  相似文献   

3.
The crystal field parameters determined from interpretation of optical spectra are used to analyze distortions of a crystal lattice in the vicinity of an impurity ion and vacancy at a Cs+ site compensating the excess positive charge in the trigonal centers of Yb3+ ions in CsCaF3 crystal. Interactions of the impurity ion with the nearest neighbors (an octahedron of F? ions) and the next nearest neighbors (a cube of Cs+ ions) are considered within the superposition model. It is established that, at formation of the trigonal center, three F? ions of the nearest octahedron, placed symmetrically along the threefold axis on the side of the vacancy, move away from the impurity ion a little and significantly deviate from this axis. The second triangle of F? ions, on the contrary, comes nearer to the impurity ion and nestles on the axis of the center a little. The three Cs+ ions, the second neighbors on the side of the vacancy, slightly come nearer to Yb3+ ion and considerably nestle on the center axis. The second triangle of Cs+ ions, from the opposite side of vacancy, also comes nearer to the paramagnetic ion and also nestles on the center axis a little. The Cs+ ion, lying on the center axis, comes considerably nearer to the impurity ion.  相似文献   

4.
An empirical relationship describing the radial dependence of the nondipole part of the anisotropic constant for the ligand hyperfine interaction in alkaline-earth fluorides is proposed. This relationship is used for calculating the distances between the magnetic ion and the fluorine ions involved in its nearest environment. The results of the calculations are in good agreement with the values obtained by other methods for both cubic and tetragonal fluorine centers in these crystals. The distances from the magnetic ion to different groups of nonequivalent fluorine ions of the nearest environment in Yb3+ trigonal centers of SrF2 and BaF2 are determined. It is found that the Yb3+ ion is slightly displaced along the trigonal axis away from the compensating fluorine ion.  相似文献   

5.
Expressions for calculating the matrix elements of the Coulomb interaction of f electrons of the isolated ion with an infinite crystal lattice have been obtained. The contribution of this interaction to the parameters of the crystal field in impurity centers Yb3+: KZnF3, CsCaF3, and Sm3+: CaF2 has been calculated.  相似文献   

6.
CaF2 crystals doped with Yb3+ ions have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy. EPR spectra of paramagnetic centers (PCs) for cubic (Tc) and tetragonal (Ttet) symmetries were identified. Empirical energy level diagrams were established and crystal field parameters were determined. Information on the CaF2∶Yb3+ phonon spectra was obtained from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyze the crystal lattice distortions in the vicinity of the Yb3+ ion. Within the framework of a superposition model, it is established that four F ions located symmetrically with respect to the fourfold axis from the side of the ion-compensator approach the impurity ion and deviate from the PC axis. The second set of four fluorine ions also approaches the Yb3+ ion and the PC axis. The ion-compensator F also approaches considerably the impurity ion.  相似文献   

7.
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   

8.
The six optical band positions and six spin-Hamiltonian parameters [g factors g, g and hyperfine structure constants A(171Yb3+), A(171Yb3+), A(173Yb3+), A(173Yb3+)] for Yb3+ ion at the tetragonal Y3+ site of KY3F10 crystal are calculated from a diagonalization (of energy matrix) method. In the method, the Hamiltonian of energy matrix contains the free-ion, crystal-field interaction, Zeeman (or magnetic) interaction and hyperfine interaction terms and so a 14×14 complete energy matrix for 4f13 ion in tetragonal crystal-field and under an external magnetic field is constructed. Diagonalizing the energy matrix, these optical and EPR spectral data are calculated together and the calculated results are in reasonable agreement with the experimental values. The signs of hyperfine structure constants A, A for the isotopes 171Yb3+ and 173Yb3+ in KY3F10 are suggested. The results are discussed.  相似文献   

9.
Electron paramagnetic resonance (EPR) spectra of doped paramagnetic crystals LiLuF4:U3+ and LiYF4:Yb3+ have been investigated at a frequency of about 9.42 GHz in the temperature range of 10–20 K. The U3+ ion spectrum is characterized by g-factors g = 1.228 and g = 2.516, and contains the hyperfine structure due to the 235U isotope with nuclear spin I = 7/2 and natural abundance of 0.71%. The observed hyperfine interaction constants are A = 81 G and A = 83.8 G. Moreover, the spectrum reveals the well-resolved superhyperfine structure (SHFS) due to two groups of four fluorine ions forming the nearest surrounding of the U3+ ion. This SHFS contains up to nine components with the spacing between components being about 12.7 G. The SHFS is observed also in the EPR spectrum of the LiYF4:Yb3+ crystal; up to 17 components with spacing of about 3.7 G may be traced. Some parameters of the effective Hamiltonian of the SHF interaction are estimated, the contribution of covalent bonding of f-electrons with ligands into these parameters is discussed. Authors' address: Igor N. Kurkin, Kazan State University, Kremlevskaya ulitsa 18, Kazan 420008, Russian Federation  相似文献   

10.
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   

11.
The pattern of lattice distortions occurring in the vicinity of Yb3+ ions during the transition of the Rb2NaYF6: Yb3+ crystal from the cubic to tetragonal phase has been revealed using all the parameters of the empirically found crystal fields for paramagnetic centers of the Yb3+ ions with cubic and tetragonal symmetry. It has been shown that the YbF6 octahedra are rotated about the fourfold axis through an angle approximately equal to 1.2°. Moreover, the octahedra themselves are deformed so that the F? ions symmetrically located in the plane perpendicular to the axis of rotation come close to the impurity ion at a distance of 0.0004 nm. The fluoride ions located on the axis of rotation, conversely, move away from the Yb3+ ion at a distance of 0.0005 nm. Based on the obtained results, it has been concluded that the total condensate of order parameters of the studied phase transition involves not only the critical rotations of octahedral groups but also the noncritical displacements of atoms in the rotated octahedra.  相似文献   

12.
Complex EPR spectra of paramagnetic centers Pb3+ formed in LiBaF3:Pb2+ crystals under X-ray irradiation are studied in the temperature range of 10–150 K. It is shown that lead ions substitute Ba2+ ions in the LiBaF3 crystal and are in the cubic-octahedral 12-fold environment of the fluorine ions. The hyperfine structure constants describing the observed spectrum are determined and parameters of superhyperfine interaction with the nearest fluorine ions are estimated.  相似文献   

13.
The electron paramagnetic resonance (EPR) spectra of impurity Ho3+ ions in monocrystals LiYF4∶Ho3+ (0.1 and 1%) with the natural abundance of6Li (7.42%) and7Li (92.58%) isotopes, and in the sample7LiYF4∶Ho3+ (0.1%) isotopically pure in7Li were taken at the temperature 4.2 K in the frequency range of 165–285 GHz. Resonance transitions between crystal field sublevels (the ground non-Kramers doublet and the nearest excited singlet) of the5I8 term were detected. The refined set of crystal field parameters and the effective constant of the magnetic hyperfine interaction were determined from the detailed analysis of the recorded spectra at frequencies varied by 0.05 GHz. The fine structure of EPR lines with intervals of about 300 MHz observed in the sample LiYF4∶Ho3+ (0.1%) can be interpreted as a result of the isotopic disorder in the Li sublattices. Direct information about energy gaps at the anticrossing points of the electron-nuclear sublevels of the ground doublet was obtained. These gaps are induced by the hyperfine interaction that mixes doublet and singlet states and by random crystal fields. Weak EPR signals from distorted single ion and pair centers of impurity Ho3+ ions were resolved. From a comparison of the measured and simulated spectra, estimates of spectral parameters of the dimer centers have been obtained.  相似文献   

14.
The magnetic properties of Yb3+ in Yb2BaCuO5 have been examined using170Yb Mössbauer spectroscopy. The quadrupole and magnetic hyperfine parameters of the Yb3+ ground doublet at each of the two sites have been obtained. The Yb3+ magnetic polarization is due uniquely to couplings with the ordered Cu2+ moments.  相似文献   

15.
The operator, which determines the contribution of processes including the polarization of central ion core to the ligand hyperfine interaction (LHFI), has been obtained in the second quantization representation in the basis of partially nonorthogonal orbitals. The contributions of the impurity Yb3+ ion to the LHFI parameters have been also calculated in Cs2NaYF6 and CsCaF3 crystals, which are determined by the mechanisms studied earlier. The single-particle orbital basis has been extended as compared to the previous work. There is a sufficiently good agreement with the experiment.  相似文献   

16.
The EPR parameters (g factors and hyperfine structure constants A) for the tetragonal Ti3+ center in cubic phase and the rhombic Ti3+ center in tetragonal phase in the neutron-irradiated SrTiO3 crystals are calculated from the third-order perturbation formulas of EPR parameters for d1 ions. These low-symmetry Ti3+ centers in both phases of SrTiO3 are due to the Ti3+ ion at “off center” on the Sr2+ site. From the calculation, the defect models (including the direction and magnitude of the Ti3+ off-center displacement) of the two Ti3+ centers in SrTiO3 are estimated and the EPR parameters of both Ti3+ centers are reasonably explained on the basis of the defect models. The results are discussed.  相似文献   

17.
The crystal field (CF) energies of the electronic ground state of Ho3+ ions in a LaCl3 host have been calculated with the set of CF parameters of Crosswhite et al. The magnetic anisotropy and the average susceptibility have been studied from room temperature down to liquid helium temperature. The g-values and the hyperfine structure parameters have been computed and compared with the experimental values. The Schottky and hyperfine heat capacities have also been determined and some interesting anomalies are predicted. All available observed properties are explained fairly well on the basis of the interaction of the ion with the CF proposed by Crosswhite et al.  相似文献   

18.
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   

19.
Exchange charge model of crystal field [B.Z. Malkin, in: A.A. Kaplyanskii, B.M. Macfarlane (Eds.), Spectroscopy of Solids Containing Rare-earth Ions, North-Holland, Amsterdam, 1987, pp. 33-50.] was used to analyze the energy level schemes of Ni2+ ion at both possible positions (octahedral and tetrahedral) in Ca3Sc2Ge3O12. The crystal field parameters were calculated from the crystal structure data; the crystal field Hamiltonian was diagonalised in the complete basis consisting of 25 wave functions of all LS terms of the Ni2+ ion. Results of calculations are in a good agreement with experimental data. From the experimental spectra available in the literature, the Huang-Rhys parameter S=3.5 and effective phonon energy were evaluated for the octahedral Ni2+ ion.  相似文献   

20.
This paper reports on the results of ligand electron-nuclear double resonance (ENDOR) investigations of T1 trigonal 157Gd3+ centers in the CaF2 compound. It is experimentally found that the nearest environment of an impurity center contains only one 19F ion. Anions in the other coordination shells are identical to those in the pure CaF2 crystal. However, 19F ions in these shells are displaced from their ideal positions in the lattice. The parameters of the ligand hyperfine interaction (LHFI) for 19F nuclei and their coordinates and displacements with respect to the positions in the lattice of the pure CaF2 crystal are determined. It is demonstrated that the unusual isotropic LHFI constant A s >0 for Gd3+ ions in the lattice with a mixed oxygen-fluorine nearest environment can be associated with the strong polarization of impurity centers in accordance with the empirical model proposed in [1], provided the structural model of the nearest environment of impurities in the T1 centers [2] is correct. This structural model is confirmed by the analysis of the isotropic hyperfine constant A(s) for 157Gd3+ centers.  相似文献   

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