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Yongrong Shen Kevin L. Bray Marek Grinberg Justyna Barzowska Irena Sókolska 《高压研究》2013,33(1-6):125-130
Abstract The effect of pressure on the luminescence spectrum of the weak field system Cr3+ : LiTaO3 is presented. By using pressure to induce a low to high crystal field strength transition, we demonstrate the ability of pressure to identify distinct dopant bonding environments in luminescent materials. 相似文献
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Fluorescence spectra of LiYF4:Pr3+ have been measured between 12,000 and 22,000 cm−1 under pressures up to 10 GPa. In total, 25 crystal field energy levels were obtained and used for the determination of free-ion and crystal field parameters under pressure. According to the nephelauxetic effect, the free-ion parameters decrease with increasing pressure. The relative decrease is larger for the Slater than for the spin-orbit coupling parameter. This behavior is consistent with former studies on Pr3+ in different crystals and can be explained by a special covalency model. According to an effective D2d symmetry, five crystal field parameters B02(f,f), B04(f,f), B44(f,f), B06(f,f), and B46(f,f) are non-zero. The pressure-induced changes of these parameters have been determined up to the maximum pressure of 10 GPa. In order to improve the calculation of the crystal field levels, the configuration interactions with the 4f16p1 configuration have been taken into account. The effect of these interactions are also analyzed under pressure and distinct improvements of the energy level calculations have been obtained. 相似文献
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Abstract Fluorescence from Nd3+ in LaCl3 is measured at 100 K under pressures up to about 10 GPa. The observed variations of the energy levels are used for the evaluation of crystal field parameters. The pressure-dependence of these parameters is compared with the previous results on Pr3+ in LaCl3. 相似文献
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A. A. Kornienko E. B. Dunina A. A. Kaminskii 《Journal of Experimental and Theoretical Physics》1999,89(6):1130-1137
A theory of the crystal field for Ln3+ ions is proposed which takes account of the difference in the effect of excited configurations on high-lying and low-lying
multiplets. The effective-operator method in third-order perturbation theory is used to obtain the Hamiltonian of the crystal
field, which in addition to the usual terms contains energy-dependent operators. Their role is discussed in detail. For the
new operators we have obtained convenient expressions which make it possible for the first time to determine the parameters
of an odd crystal field on the basis of an analysis of the structure of the energy spectrum. Theory is compared with experiment
for the laser crystals Y3Al5O12:Tm3+ and LiYF4:Pr3+. Taking the new terms of the crystal-field Hamiltonian into account produces an additional shift of individual levels within
the limits from −40 cm−1 to 40 cm−1 and makes it possible in a number of cases not only to substantially reduce the value of the standard deviation, but also
to obtain the correct arrangement of levels.
Zh. éksp. Teor. Fiz. 116, 2087–2102 (December 1999) 相似文献
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Abstract The luminescence spectrum of Cs2NaScCl6:Pr3+ (0.1 at.%) has been recorded at temperatures down to 10 K and assigned between 20,800 and 9900 cm?1. Twenty‐three energy levels of the 4f2 configuration Pr3+ ion were located and then fitted by the conventional 4f2 crystal field calculation, as well as by a configuration interaction assisted crystal field (CIACF) calculation. The latter gave a much better fit. A comparison of the fit for Cs2NaScCl6:Pr3+ with fits upon the same set of energy levels in Cs2NaYCl6:Pr3+ and Cs2NaPrCl6, where the fifth nearest neighbor of Pr3+ is changed and the lattice parameter increases along this series, shows a decrease in the magnitudes of the crystal field parameters, which were also semiquantitatively simulated. Several facets of the emission spectra are interesting, including the observation of weak progressions in the totally symmetric Pr–Cl stretching vibration and the occurrences of the resonance of electronic and vibronic states. The spectra of Cs2NaScCl6:Pr3+ (1 at.%) differ considerably from those of the more dilute system and show that other species are formed rather than a complete substitution of the Sc3+ sites by Pr3+. 相似文献
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An investigation on the magneto-optic properties of terbium gallium garnet under high magnetic field 下载免费PDF全文
The superexchange interaction on a magnetic ion may be represented by an effective field Hm = $\lambda$M in some paramagnetic materials, here λ is the coefficient of effective field and M = $\chi$He with $\chi$ being the magnetic susceptibility and He being the applied field. The variation of the equivalent $\lambda_{\chi}$with the dynamic applied field is given and the crystal field-splitting levels of the excited configuration 4f75d1 of the Tb3+ ion are calculated in the Tb3Ga5O12. By means of the effective field Hm and the applied field He, the Faraday rotation of Tb3Ga5O12 at 6 K and 41 K, under the high magnetic field and at 0.63 μm wavelength, are presented. Our calculated results are in agreement with the experimental data. 相似文献
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In this paper we demonstrate that two independent methods of calculations (DFT based ab initio and semi-empirical crystal field theory) can be used to form a complementary picture of the optical and electronic properties of the doped host and impurity ion. The crystals considered in the present paper are: (i) YAlO3:Ce3+ and (ii) two dominant phases of TiO2—rutile and anatase. As an example, detailed calculations of the band structure and crystal field energy level scheme of YAlO3:Ce3+ are reported. From the analysis of the band structure and density of states, the character of the YAlO3 energetic bands and positions of the Ce impurity energy levels were established. It was also shown how the ab initio methods can be used for calculations of the structural properties of solids under elevated pressure. Taking the two dominant phases of TiO2 as an example, it was demonstrated how the elastic properties can be extracted from the calculated unit cell’s volume at different pressures. Particular attention was paid to the microscopic effects of crystal field, which were evidenced by the pressure-induced changes of the structure and shape of distribution of the Ti 3d electrons density of states. It was demonstrated how the difference in crystal structure of the anatase and rutile phases leads to remarkable difference in microscopic crystal field effects, which was explained by different Ti-O distances in both phases. In addition, the pressure dependence of the band gaps for anatase and rutile was investigated. It was shown that the hydrostatic pressure leads to the band gap narrowing in anatase and band gap widening in rutile, with pressure coefficients +0.00681 eV/GPa for rutile and −0.0088 eV/GPa for anatase. 相似文献
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Noritaka Kuroda Yasuo Oeda Giyw Kido Masayasu Takeda Yuichiro Nishina Yasuaki Nakagawa 《高压研究》2013,33(1):65-66
Abstract The magneto-optical spectra of the R1 and R2 lines of Cr3+ ions in alexandrite have been measured under hydrostatic pressures and magnetic fields up to 6 GPa and 15 T, respectively. The spins of the excited states, 2E, have the Heisenberg-type characters at atmospheric pressure, though the g-values are anisotropic with the values between 1.3 and 2.0. The g-values for the direction parallel to the α-axis remain unchanged with increasing pressure, while for the directions normal to the α-axis they are reduced appreciably. The fine structure parameters of spins in the ground state, 4A2, exhibit quite a similar behavior. The R1-R2 splitting is reduced also by pressure. These properties are the evidences that the spins of the 2E states become of the king-type under pressures above about 15 GPa. The mechanism of such the change of spin character is discussed quantitatively on the basis of a crystal field model. 相似文献
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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
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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
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Summary Chromium doped single crystals of Forsterite where investigated directly under the influence of uniaxial pressure in situ by ESR. The two Cr3+ centres M1 and M2 exhibit distinct response to the action of pressure on the crystal as a whole. The pressure effects are manifested in remarkable changes of the line width of the fine structure transitions. Uniaxial pressure in the MPa range induces nearly symmetrical distribution of distortions of the coordination polyhedra of the Cr3+ centres accompanied by reorientation effects. 相似文献
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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
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This work investigates the pressure-induced variation of the local structure around Cu2+ as well as the crystal structure in Rb2CuCl4(H2O)2 through XAS and XRD techniques. The application of pressure induces a structural change in the Jahn-Teller (JT) [Formula: See Text] complex from axially elongated to compressed. This change leads to the closing of the 2D JT distortion related to the four in-plane Cl? ligands, which are responsible for the antiferrodistortive structure displayed by the crystal. It is shown that the presence of water ligands enhances a JT release. Their associated axial ligand-field favours the occurrence of such a local structural transition below the metallization pressure. The results are compared with recent pressure experiments on A2CuCl4 systems. 相似文献
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V. P. Glazkov B. N. Savenko V. A. Somenkov D. V. Sheptyakov S. Sh. Shilstein 《高压研究》2013,33(3-6):201-207
Abstract The crystal structure of Nd2CuO4 has been studied by neutron diffraction at pressure up to 5 Gpa. The volume compressibility value was determined as 5·6·10?3/Gpa. The decrease of positional parameter of neodymium at high pressure has been observed. This structural change is explained by pressure induced neodymium ions charge increase. 相似文献
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Abstract The kinetics of crystallization of eutectic alloys Al100-xSix (χ=12, 18, 26 at.%) was investigated under pressures p=0.5, 2.5, 4.5 GPa. The values of supercooling and average grain size of silicon crystals were determined for alloys quenched from melt under different pressures with the cooling rate 103 K/s. The data obtained were used to evaluate quantitatively the pressure dependences of surface tension (between melt and crystal) and activation energy of crystal growth which, in turn, have made it possible to determine the relative change of nucleation frequency and of the rate of crystal growth with pressure. The possibility is shown, based on the investigation of mechanical properties of the samples obtained under high pressure, for improving the strength and the plasticity of A1-Si alloys by means of high pressure-high temperature treatment. 相似文献
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I. O. B. Ewa 《光谱学快报》2013,46(5):701-708
Abstract The basic principles of Electron Spin Resonance (ESR) as applicable in crystal field characterization of paramagnetic species has been outlined. Fundamental concepts of the precessional motion of electrons and their magnetic moments at resonance were developed. The theory of ESR based on the response of unpaired electron(s) as they undergo spin-spin or spin-lattice relaxation when subjected to strong external magnetic fields was examined. Ions of the O? 2 group adsorbed on TiO2 were studied using a Varian Spectrometer. The resulting spectral diagrams obtained were used in calculating the g-factors which gave results for orthorhombic crystal symmetry for O? 2 ions in TiO2. 相似文献