Luminescence of nematic lanthanide-containing mixtures

The possibility of obtaining eutectic binary nematic liquid crystal systems containing lanthanide mesogens was studied. As lanthanide mesogens, we used lanthanide(III) tris-(β-diketonate) adducts exhibiting nematic mesomorphism. The luminescence of the compositions containing Eu(III) adducts was investigated.     

Phase equilibria and isomorphism in the LiVWO<Subscript>6</Subscript>-NaVWO<Subscript>6</Subscript> system

Compounds of composition Li _x Na_{1 − x} VWO₆ (0 ≤ x ≤ 1), which are synthetic analogues of brannerite-type minerals, were produced for the first time by solid-state synthesis at high temperatures. The structure of the compounds and their unlimited miscibility in the solid phase in the LiVWO₆-NaVWO₆ binary system were determined by X-ray diffraction. The phase equilibrium diagram was studied by differential thermal analysis together with thermodynamic modeling. It was found that the system under investigation is described by the regular solid solutions model.     

Crystal structure and magnetic anisotropy of ludwigite Co<Subscript>2</Subscript>FeO<Subscript>2</Subscript>BO<Subscript>3</Subscript>

Co₃O₂BO₃ and Co₂FeO₂BO₃ single crystals with a ludwigite structure are fabricated, and their crystal structure and magnetic properties are studied in detail. Substituted ludwigite Co₂FeO₂BO₃ undergoes two-stage magnetic ordering at the temperatures characteristic of Fe₃O₂BO₃ (T _N1 ≈ 110 K, T _N2 ≈ 70 K) rather than Co₃O₂BO₃ (T _N = 42 K). This effect is explained in terms of preferred occupation of nonequivalent crystallographic positions by iron, which was detected by X-ray diffraction. Both materials exhibit a pronounced uniaxial magnetic anisotropy. Crystallographic direction b is an easy magnetization axis. Upon iron substitution, the cobalt ludwigite acquires a very high magnetic hardness.     

Intramolecular energy transfer in mesogenic europium (III) adduct

The absorption and emission spectra of a liquid-crystalline melt prepared on the basis of a synthesized mesogenic europium (III) adduct are studied in the temperature range from 77 to 348 K. The main channels and rate constants of intramolecular energy transfer from ligands to Eu (III) ions are determined from the absorption and luminescence spectra and luminescence kinetics of the sample under study. It is shown that the liquid-crystalline melt of the europium (III) adduct has a high photostability and an intense luminescence in the temperature range from 77 to 300 K, which allows one to consider it as a promising material for optoelectronic devices. Above room temperature, the relaxation time of the ⁵ D ₀ level of Eu (III) ions sharply shortens. An analysis of the kinetics of the luminescence corresponding to the ⁵ D ₀ → ⁷ F ₂ transition shows that the relaxation of the ⁵ D ₀ level in the temperature range from 300 to 348 K occurs through a charge-transfer state.