Vibronic spectra of Rb2NaTmF6 elpasolite single crystal

Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 5, pp. 94–104, September–October, 1995.     

Excitation spectra of ferromagnets with crystal fields

We have investigated the ferromagnetic phase transition and excitation spectrum of systems, such as the rare earths, where the crystalline fields are significant in determining the magnetic properties. Using the full level scheme appropriate to a system ofJ-4 ions in a crystal field of cubic symmetry and assuming a Heisenberg interaction, we have calculated the full temperature- andq-dependence of the dynamic susceptibility within the RPA, both in the paramagnetic and ordered regimes. Variations in behavior, both with changes in crystal field parameter and with changes in magnetic interaction strength are discussed, and emphasis is placed on the limiting case which corresponds to current experiments in the light rare earths.     

Vibronic spectra of matrix-isolated lead sulfide

Vibronic spectra are reported for lead sulfide in argon, krypton and SF₆ matrices at low temperatures. Emission stimulated by laser line irradiation of PbS is observed from the v′ = 0 level of three electronic states lying at about 14 500, 18 500 and 21 500 cm^?1 above the ground state. Emission is also observed from an excited state of Pb₂S₂ at about 17 000 cm^?1. In addition, the laser radiation gives rise to the vibrational Raman spectrum of PbS in argon at 423.2 cm^?1 and to a very weak Raman band at 297 ± 2 cm^?1 which we attribute to Pb₂S₂.The effects of temperature on the matrix spectra, of matrix material on the band origins, and of matrix concentration on the vibrational relaxation process, and the apparent degrees of coupling among the electronic states have all been examined. The electronic absorption spectrum of PbS in Ar is reported and the matrix data are compared with available information on gaseous PbS.     

Crystal field of octahedral Yb3+ centers in a CsCaF3 crystal

The phenomenological crystal-field potentials of cubic and trigonal Yb³⁺ centers in a CsCaF₃ crystal have been determined from the experimental energy-level schemes. These potentials are compared with the potentials of the analogous centers in the isomorphic hosts KMgF₃ and KZnF₃. Information about the phonon spectrum of a CsCaF₃:Yb crystal was obtained from the electronic-vibrational structure of the luminescence spectra. Fiz. Tverd. Tela (St. Petersburg) 39, 1030–1034 (June 1997)     

Vibronic Frenkel exciton in a soft-mode crystal

The pair electron-hole Jahn-Teller effect, which is realized on degenerate states of a vibronic Frenkel exciton (VFE) in soft-mode crystals, is considered. It is shown that the vibronic effect in a VFE can be significantly enhanced in crystals having soft lattice modes. The occurrence of strong local order-disorder fluctuations in this situation is predicted. The manifestations of VFEs localized at impurities in soft matrices (Cr³⁺ in SrTiO₃, Fe⁵⁺ in KTaO₃, and Mn⁵⁺ in TbVO₄ and TbPO₄) are considered. The possibility of fluctuation effects related to VFEs in nominally pure soft-mode crystals (SrTiO₃ and BaTiO₃) is discussed.     

Intense-field alignment of molecules confined in octahedral fields

The combined effect of static octahedral potential and anisotropic interactions with intense linearly polarized light on the rotational motion of linear molecules is investigated. Avoided crossings of quantized energy levels corresponding to pendular states with different degrees of alignment are found by varying the strength parameters for the light and static fields. High alignment is achieved for both cooperative and competitive choices of the relative directionality of the two fields, thus presenting means for controlling the dynamics of impurity centers with respect to the surrounding media.     

光致发光光谱研究金刚石光学中心的振动结构

金刚石中不同的缺陷中心具有不同的振动结构. 间隙原子相关中心在离开零声子线165 meV之外存在强且尖锐的局部振动模; 空位相关中心具有很强的振动耦合, 在其零声子线之后出现很强且宽的声子边带, 而在165 meV之外却观察不到局部振动模, 且对于仅涉及一个空位的缺陷来说, 其振动都与一个能量约为42 meV的声子或一个能量约为67 meV的声子或两声子有关.     

Vibronic transitions in the absorption spectrum of a U3+-doped elpasolite single crystal

Conclusions We have presented the absorption bands associated with f−f and f−d transitions. The investigated ion was placed in the center of symmetry. For that reason pure electric dipole f−f transitions are forbidden, but thet are allowed for f−d transitions. Nevertheless, pronounced vibronic transitions were obseved not only in the f−f lines but also for f−d bands. An assignment of the observed lines supported by previously reported Raman and IR spectra is proposed. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 4, pp. 58–62, July–August, 1995.     

Theoretical explanation of optical absorption spectra and covalent effect of Ni2+ ions in octahedral sites of Ca3Sc2Ge3O12 crystal

The optical absorption spectra (d-d transition bands) and covalent effect of Ni²⁺ ions in octahedral sites of Ca₃Sc₂Ge₃O₁₂ crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is R_i?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni²⁺ center in Ca₃Sc₂Ge₃O₁₂ crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni²⁺ ion in the octahedral site of Ga₃Sc₂Ge₃O₁₂ is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d⁸ ions in octahedral lattices.     

Vibronic spectra of aluminium monochloride relevant to circumstellar molecule

The A^1Π→ X^1Σ^+ transition system of aluminium monochloride is determined by using ab initio quantum chemistry.Based on the multi-reference configuration interaction method in conjugate to the Davidson correction(MRCI + Q), the potential energy curves(PECs) of the three electronic states are obtained. Transition dipole moments(TDMs) and the vibrational energy levels are studied by employing the aug-cc-pwCV5Z-DK basis set with 4220-active space. The rovibrational constants are first determined from the analytic potential by solving the rovibrational Schr ¨odinger equation, and then the spectroscopic constants are determined by fitting the vibrational levels, and these values are well consistent with the experimental data. The effect of spin–orbit coupling(SOC) on the spectra and vibrational properties are evaluated.The results show that the SOC effect has almost no influence on the spectroscopic constants of AlCl molecules. For the A^1Π→ X^1Σ^+transition, the highly diagonalized Frank–Condon factor(FCF) is f(00)=0.9988. Additionally, Einstein coefficients and radiative lifetimes are studied, where the vibrational bands include ν'= 0–19→ν'=0–9. The ro-vibrational intensity is calculated at a temperature of 296 K, which can have certain astrophysical applications. At present, there is no report on the calculation of Al Cl ro-vibrational intensity, so we hope that our results will be useful in analyzing the interstellar Al Cl based on the absorption from A^1Π→ X^1Σ^+.     

Optical spectra of octahedral cubic and trigonal Yb3+ impurity centers in KMgF3 and KZnF3 crystals

Groups of lines corresponding to octahedral cubic and trigonal impurity centers have been isolated in complex many-center luminescence and excitation spectra of Yb³⁺-doped KMgF₃ and KZnF₃ crystals. The crystal-field potentials derived from the spectra are in good agreement with those of similar centers in CsCaF₃:Yb³⁺ crystal studied earlier. Fiz. Tverd. Tela (St. Petersburg) 40, 2029–2034 (November 1998)