In this paper we review the spectroscopic properties of three transition metal ions - Mn4+, Cr3+ and Ni2+ - in crystals and establish a relationship between the energies of the lowest in energy spin-forbidden transitions and covalence of the “metal –ligand” chemical bonds. A new parameter β1=(BB0)2+(CC0)2 (where (B, C (B0, C0) are the Racah parameters of the ions in a crystal (free state), respectively) is shown to determine the energy of the above-mentioned transitions. The considered ions can be used as reliable probes of the covalent effects in various hosts. Several practical recommendations on how to tune the spin-forbidden transitions energy to meet specific needs are suggested.

A feeding trial was conducted to evaluate the effect of aflatoxin (AF)-contaminated diets on growth and hematological and immunological parameters. Low doses of aflatoxins (140 and 280 ppb) were included in a corn-soybean diet provided for ad libitum consumption to 36 weanling piglets for a period of 4 wk. A "dose-related" decrease in weight gain was observed in treated animals. This effect was significant (P < 0.05) in the 280 ppb-treated group compared to the control group. Ingestion of AF-contaminated feed at either level had no effect on total red blood cell numbers or on their relative number of lymphocytes, monocytes, neutrophils, basophils, and eosinophils in blood. Likewise, AF did not alter globulin, albumins, or total protein concentrations in serum, nor did AF alter the expression of regulatory cytokines produced by either Th1 (IL-2) or Th2 (IL-4) lymphocyte subsets in phytohemagglutinin-stimulated blood samples. By contrast, AF had a biphasic effect on total white blood cell number; the low dose of AF (140 ppb) decreased the total number of white blood cells, whereas the high dose (280 ppb) had the opposite effect. Consumption of AF also increased the concentration of gamma-globulin in the serum. A reduced immune response induced by Mycoplasma agalactiae in the 280-ppb-treated group was also observed. Cytokine mRNA expression in phytohemagglutinin-stimulated blood cells indicated that AF decreased proinflammatory (IL-1beta, TNF-alpha) and increased anti-inflammatory (IL-10) cytokine mRNA expression. These results demonstrate that low doses of AF depress growth and alter many aspects of humoral and cellular immunity in pigs.

An analysis of the energy level structure of Cr 3+ ions in Cs 2 NaAlF 6 crystal is performed using the exchange charge model (ECM) together with the crystal field analysis/microscopic spin Hamiltonian (CFA/MSH) computer package. Utilizing the crystal structure data, our approach enables modelling of the crystal field parameters (CFPs) and thus the energy level structure for Cr 3+ ions at the two crystallographically inequivalent sites in Cs 2 NaAlF 6 . Using the ECM initial adjustment procedure, the CFPs are calculated in the crystallographic axis system centred at the Cr 3+ ion at each site. Additionally the CFPs are also calculated using the superposition model (SPM). The ECM and SPM predicted CFP values match very well. Consideration of the symmetry aspects for the soobtained CFP datasets reveals that the latter axis system matches the symmetryadapted axis system related directly to the six Cr-F bonds well. Using the ECM predicted CFPs as an input for the CFA/MSH package, the complete energy level schemes are calculated for Cr 3+ ions at the two sites. Comparison of the theoretical results with the experimental spectroscopic data yields satisfactory agreement. Our results confirm that the actual symmetry at both impurity sites I and II in the Cs 2 NaAlF 6 :Cr 3+ system is trigonal D 3d . The ECM predicted CFPs may be used as the initial (starting) parameters for simulations and fittings of the energy levels for Cr 3+ ions in structurally similar hosts.

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ABSTRACT:The aim of this study is to establish a new representation for the dynamic algebra of the Morse oscillator and to establish the raising and lowering operators based on the properties of the confluent hypergeometric functions.Using the representation we have obtained a recurrent analytic method for the calculus of the Franck᎐Condon factors.

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A detailed microscopic study of the crystal field strength 10Dq for different interionic distances in cubic SrTiO(3) doped with three isoelectronic ions (Cr(3+), Mn(4+) and Fe(5+)) was performed. The exchange charge model of the crystal field was used to calculate the 10Dq values at different distances between impurity ions and ligands. The obtained results were represented by the power laws 1/R(n), with n = 4.9050, 5.7990 and 6.5497 for Cr(3+), Mn(4+) and Fe(5+), respectively. For the first time the role of two different contributions (the point charge and exchange charge) into the total crystal field strength was studied separately. With the obtained 10Dq(R) dependences, a number of important physical quantities describing the optical and dynamical properties of impurity centers (such as the constants of the electron-vibrational interaction, Huang-Rhys parameters, Stokes' shifts, Jahn-Teller stabilization energies, changes of the chemical bond lengths due to the combined effect of the local vibrational normal modes, bulk modulus and Grüneisen constants for the a(1g) normal mode) were calculated. The obtained results are in good agreement with available experimental data and can be readily applied for analysis of the optical spectra, electron-vibrational interaction and pressure effects for these and other similar systems.