Magneto-optical spectroscopy of Yb ions in huntite structure

We report the first measurements of magnetic circular dichroism (MCD) and magneto-optical activity (ratio of zero moments of MCD and absorption bands) of Yb³⁺ ion in the trigonal single crystals Yb_xTm_1−xAl₃(BO₃)₄ as a function of temperature in the range of 100-293 K. Magneto-optical activity follows the Curie-Weiss law with the Weiss constant θ=−55 K for Yb_0.1Tm_0.9Al₃(BO₃)₄ crystal. The value and origin of the magneto-optical activity is theoretically analyzed.     

Spectroscopic properties and structure of the ErFe3(BO3)4 single crystal

Single crystals of the ErFe₃(BO₃)₄ borate were synthesized and their structure was studied. Absorption spectra of the Er³⁺ ion in σ- and π-polarizations of f-f transitions ⁴ I _15/2 → ⁴ I _13/2, ⁴ I _11/2, ⁴ I _9/2, ⁴ F _9/2, ⁴ S _3/2, ² H _11/2, and ⁴ F _7/2 were measured. The refractive index and birefringence were measured as a function of the wavelength. The transition intensities were analyzed within the Judd-Ofelt theory, and the following parameters of the theory were obtained: Ω₂ = 7.056 × 10^?20 cm², Ω₄ = 1.886 × 10^?20 cm², and Ω₆ = 2.238 × 10^?20 cm². Using these parameters, the radiative transition probabilities, luminescence branching ratios, and radiative lifetimes of multiplets were calculated.     

QSPR approach to the calculation of rate constants of homolysis of nitro compounds in different states of aggregation

A method for the theoretical estimation and prediction of rate constants of homolysis of nitro compounds of different chemical classes in the gas phase is proposed on the basis of the QSPR approach.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1653–1656, September, 1995.The authors express gratitude to B. A. Lur'e (D. I. Mendelev Moscow Academy of Chemical Technology) for fruitful advice during discussion of the results.     

Magneto-optical properties of Dy<Superscript>3+</Superscript> in oxide glasses: The origin of the magneto-optical activity of <Emphasis Type="Italic">f-f</Emphasis> transitions and its anomalous temperature dependence

The temperature dependence of the absorption spectra and magnetic circular dichroism due to f-f transitions from the ⁶ H _15/2 to ⁶ F _5/2 and ⁶(F _7/2 + H _5/2) states in the Dy³⁺ ion in (Dy₂O₃-P₂O₅-SiO₂-GeO₂) and (Dy₂O₃-La₂O₃-Al₂O₃-B₂O₃-SiO₂-GeO₂) glasses and the temperature dependence of the Faraday effect were studied. The temperature dependence of the Faraday effect caused by f-d transitions was found to differ from that of the magnetic circular dichroism due to f-f transitions. It was shown that f-f transitions occur preferentially in Dy³⁺ ions associated into clusters. The origin of the paramagnetic magneto-optical activity of f-f transitions was analyzed. It was shown that the contributions to this activity can differ in value and sign and that the ratio between these contributions depends on the transition type. In some cases, this difference results in an anomalous temperature dependence of the magneto-optical activity.     

Spectroscopic manifestations of local crystal distortions in excited 4f states in crystals of huntite structure

Optical absorption spectra of YbAl₃(BO₃)₄, TmAl₃(BO₃)₄ and TbFe₃(BO₃)₄ trigonal crystals have been studied in temperature range 2–300 K. Temperature behavior of absorption lines parameters has shown, that during some f-f transitions the local environment of rare earth ions undergo distortions, which are absent in the ground state.     

Polarized absorption spectra and spectroscopic parameters of Tm3+ in the TmAl3(BO3)4 single crystal

High-optical-quality single crystals of the TmAl₃(BO₃)₄ compound were synthesized from a solution in the melt. The absorption spectra in the σ and π polarizations for the ³ H ₆ → ³ F ₄, ³ H ₆ → ³ H ₅, ³ H ₆ → ³ H ₄, ³ H ₆ → ³ F ₃, ³ H ₆ → ³ F ₂, ³ H ₆ → ¹ G ₄, and ³ H ₆ → ¹ D ₂ transitions in the Tm³⁺ ion were recorded at room temperature. The transition intensities were analyzed in the framework of the Judd-Ofelt theory generalized to the case of anisotropic crystals, and the following parameters of the theory were obtained: Ω₂ = 6.14 × 10^?20 cm², Ω₄ = 3.09 × 10^?20 cm², and Ω₆ = 2.04 × 10^?20 cm². The lifetimes and the branching ratios were determined for all possible transitions.     

Giant natural circular dichroism of vibronic transitions in HoAl3(BO3)4

The giant natural optical activity of vibronic replicas of the f–f ⁵ I ₈ → ⁵ F ₂ transition in HoAl₃(BO₃)₄ is observed. It exceeds the optical activity related to purely electronic transitions by two orders of magnitude and corresponds to the almost complete circular polarization of the transitions. This effect is explained by the local distortions of the crystal in the excited electronic state, which lead to the mixing of electron and vibrational wavefunctions and, as a consequence, to the delocalization of the vibronic wavefunction and the enhancement of spatial dispersion, which is responsible for the optical activity.     

Study of the Adsorption Activity of Skeletal Nickel with Respect to Reactive Hydrogen by Simultaneous Thermal Analysis Mass Spectrometry

A method for the determination of the total amounts and physical parameters of adsorbed individual hydrogen species on the surface and in the bulk of metal catalysts of liquid-phase hydrogenation reactions by simultaneous thermal analysis mass spectrometry was proposed. The adsorptions of reactive hydrogen on a skeletal nickel catalyst in an aqueous medium were estimated. The concentrations of metal-hydrogen complexes with different binding energies on the surface of the catalyst in the liquid phase were determined by a direct experimental method.

     

Comparison of the Absorption Spectra of Nd3+ Ions in the NdFe3(BO3)4, Nd0.5Gd0.5Fe3(BO3)4, and Ho0.75Nd0.25Fe3(BO3)4 Crystals

Physics of the Solid State - The polarized optical absorption spectra in the region of a series of the f–f &nbsp;transitions of Nd3+ ions in the Ho0.75Nd0.25Fe3(BO3)4,...     

Influence of magnetic ordering on electronic structure of Tb<Superscript>3+</Superscript> ion in TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal

Optical absorption spectra of trigonal crystal TbFe₃(BO₃)₄ have been studied in the region of ⁷F₆ → ⁵D₄ transition in Tb³⁺ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb³⁺ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice, have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be due to the abrupt change of equilibrium geometry of the local Tb³⁺ ion environment only in the excited state of the Tb³⁺ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb³⁺ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has been shown that the ground state (in D ₃ symmetry approximation) consists of two close singlet states of A ₁ and A ₂ type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of the excited electronic states relative to that of the ground state have been experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines has been observed in the vicinity of the TbFe₃(BO₃)₄ structural phase transition. The temperature interval of coexistence of the phases is about 3 K.