Парамагнитные центры в легированном хромом монокристалле Na-=SUB=-5-=/SUB=-AlF-=SUB=-2-=/SUB=-(PO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=-

The paramagnetic resonance of Na5AlF2(PO4)2 single crystals with chromium impurity was studied. The Cr3+ centers have been found to replace the triclinic Al3+ positions. In the local coordinate system, the spectra of these centers were described by the spin Hamiltonian of rhombic symmetry. In addition, vanadium centers and unidentified triclinic symmetry centers have been observed.

Laws of reflection and refraction of TE and TM polarization waves on the border of rhombic crystals

The article analytically solves the problem of reflection and refraction of electromagnetic plane waves of different polarization at the boundary of anisotropic half-spaces of rhombic symmetry. Based on the matrix method, the angles of refraction of electromagnetic waves of different polarization, the amplitudes of the reflected and refracted waves, the angles that determine the direction of the group velocities and vectors of the flow of electromagnetic energy, the magnitudes of the flows of electromagnetic energy and their components depending on the direction of the wave vector of the incident wave are determined. The determination of the angles of total internal reflection and the refractive index of electromagnetic waves of different polarization is considered. A significantly different dependence of the kinematic and energy characteristics of electromagnetic waves of different polarization on the anisotropy of the magnetic and dielectric tensors is shown. For electromagnetic waves, the polarization of which is determined by the component of the electric tension vector perpendicular to the wave propagation plane (TE wave), the characteristics of the reflected and refracted waves, the velocity indicatrix, the propagation angles, etc. determined primarily by the components of the magnetic permeability tensor. In the case of electromagnetic waves, when the polarization is determined by the component of the magnetic field (TM wave), perpendicular to the plane of wave propagation, all characteristics depend mainly on the components of the dielectric constant. The validity of the Fresnel formulas for determining the coefficients of reflected and refracted waves at the boundary of anisotropic media of rhombic symmetry is shown. However, in this case, the components of the wave vectors included in the Fresnel formulas are determined by their indicatrices. In addition, it is necessary to take into account the dependence of these components on the angle of refraction in the second medium

Role of aluminum on the physical and spectroscopic properties of chromium-doped strontium alumino borate glasses

The glass samples were prepared in accordance with the formula: (30-x)SrO–xAl2O3–69.8B2O3–0.2Cr2O3 (0 [Formula: see text]x [Formula: see text] 15 mol %) by melt quenching method. The absence of Bragg’s peaks confirmed the amorphous nature of the prepared glass samples. It was observed that the molar volume was increasing while the density is decreasing with increasing of Al2O3 content. Optical absorption study was performed to evaluate the optical bandgap, oxygen packing density, ionic packing density and Urbach energies. The Racah parameters (B and C) and D[Formula: see text]/B ratio have been calculated. Fourier transform infrared (FTIR) spectra recorded in the region from 400–1600 cm[Formula: see text] at room-temperature (RT) confirmed the formation of BO3, BO4 and AlO4 groups upon the addition of strontium oxide as modifier. The Raman spectra of all the glasses recorded over continuous spectral range 200–1600 cm[Formula: see text] exhibited different spectral bands. The EPR spectra recorded at 9.7 GHz (X-band frequency) have four resonance signals. The signal at g [Formula: see text] 5.33 is due to Cr[Formula: see text] ion sites of rhombic symmetry and signal at g [Formula: see text] 1.97 is due to contribution from Cr[Formula: see text] and Cr[Formula: see text] ion pairs.

EPR spectra of a new radiation-induced paramagnetic centre in kaolins

The EPR spectrum of a previously unreported paramagnetic centre formed in kaolin minerals by exposure to γ radiation is described. This centre, which is referred to here as the ‘C-centre’, was seen initially during an investigation of the radiation dose response of the EPR signal in the natural Lampang kaolin from northern Thailand, and its EPR properties are now presented for a purified sample from this material. They suggest a paramagnetic centre with rhombic symmetry based on O− associated with a single 27Al atom. Computer simulations suggest spin Hamiltonian parameters of g1 = 1.976, g3 = 2.0417 and A(27Al) = 2.10 mT, with g2 ≈ 2.01. This C-centre was also seen as a minor radiationinduced component in both crude and purified Ranong kaolin samples, along with a stronger signal from the B-centre radical. It seems to be associated with the kaolinite component, but was lost on annealing to 300°C after which only the signal from the A-centre was visible.

A Theoretical Study on the Spin-Hamiltonian Parameters for Samarium(III) Ion in Potassium Yttrium Tungstate Crystal

The nine spin-Hamiltonian (SH) parameters (g-factors gi and hyperfine structure constants 147Ai and 149Ai for 147Sm3+ and 149Sm3+ isotopes, where i = x, y, z) for the Samarium(III) ion in monoclinic potassium yttrium tungstate [KY(WO4)2] crystal are calculated within the rhombic symmetry approximation from a diagonalization of energy matrix method. Differing from the conventional diagonalization method used in the calculation of crystal-field levels, in the present method, we attach the Zeeman (or magnetic) and hyperfine interaction terms to the conventional Hamiltonian and construct the 66×66 energy matrix for 4f5 ions in rhombic crystal field and under an external magnetic field by considering all the ground-term multiplets 4HJ. The calculated results are in reasonable agreement with the experimental values

Studies on the EPR Parameters for the Rhombic Co2+ Center in Magnesium Acetate

The electron paramagnetic resonance (EPR) g factors gi (i = x,y, z) and the hyperfine structure constants Ai for the rhombic Co2+ center in magnesium acetate are theoretically studied from the perturbation formulas of these parameters for a 3d7 ion under rhombic symmetry. In these formulas, the contributions from the admixture among different states, covalency effect and rhombic crystal-fields are taken into account. The related crystal-field parameters are determined from the superposition model and the local geometrical relationship of the impurity center. The calculated results show reasonable agreement with the observed values. In addition, the nuclear quadrupole interaction constant Q is analyzed, and its negative sign is verified theoretically.

Modulation of cytochrome c spin states by lipid acyl chains: a continuous-wave electron paramagnetic resonance (CW-EPR) study of haem iron

This work is a systematic study, showing a clear correlation between the nature of the lipid acyl chain and the spin states of cytochrome c interacting with different types of lipid membranes. According to the lipid acyl chain type, and the head group charge present in the bilayer, three spin states of cytochrome c were observed in different proportions: the native cytochrome c low spin state with rhombic symmetry (spin 1/2, g//=3.07 and g⊥=2.23), a low spin state with less rhombic symmetry (spin 1/2, g1 = 2.902, g2 = 2.225, and g3 = 1.510) and the high spin state (spin 5/2, g// = 6.0 and g⊥ = 2.0). The proportion of the spin states of cytochrome c bound to bilayers was also dependent on the lipid/protein ratio, suggesting the existence of two or more protein sites interacting with the lipids. The lipid-induced alterations in the symmetry and spin states of cytochrome c exhibited partial reversibility when the ionic strength was increased, which reinforces the crucial role played by the electrostatic interaction with the lipid bilayer. Different cytochrome c spin states exhibited corresponding modifications in the haemprotein UV/visible spectra, particularly in the Q-band associated with loss of the 695nm band and appearance of a band in the region of 600—650nm. The observed reactivity of cytochrome c with oxidized forms of unsaturated lipids reinforces the possibility of the acyl chain insertion in the haemprotein structure.