Himiâ vysokih ènergij

The luminescent chemosensory properties of polymer composites doped with Eu(III) carboxylated dibenzoylmethanates were studied. It was shown that the interaction of the composites with ammonia and amine vapors leads to an increase in the luminescence intensity of the complexes. The obtained chemosensory polymeric compositions with the effect of “switching on” luminescence when exposed to analytes are promising for environmental monitoring.

The spatial-structural models of clusters of rare-earth-doped aluminum-yttrium garnet−Nd/Sm/Eu/Gd:YAG−were optimized using the DFT/uB3PW91/SDD method to achieve minimum potential energy. The characteristic bond lengths, angles, charge values, as well as their changes upon substitution of one yttrium atom by Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺ ions were determined. The calculation of IR spectra and the correlation of absorption bands of calculated and recorded wave numbers for crystalline YAG and Nd/Sm/Eu/Gd: YAG nanoclusters were performed. The electronic spectrum for Nd/Sm/Eu:YAG models was calculated by the TD-SCF/gen/def2-SVP method. The energies of the levels were determined and the band gap was calculated.

Polymer luminescent compositions based on polystyrene and polycarbonate doped with symmetrical and asymmetrical curcuminoids of boron difluoride were obtained. The effect of substituents in dye molecules, polymer matrix and phosphor concentration on the spectral properties of polymer composites was studied. With an increase in the electron-donor effect of substituents, a bathochromic shift of the luminescence maxima of symmetric and asymmetric phosphors is observed. Positive solvatochromism for boron difluoride curcuminoids in polymers manifests itself for asymmetric curcuminoids. For films, a bathochromic shift of luminescence is observed with an increase in the phosphor concentration from 0.01 to 0.5%. In a PC film doped with a symmetric dye with a methoxy group, delayed fluorescence due to the formation of excimers was detected at room temperature.

The degradation of phenylalanine in an acidic aqueous solution (pH 3) with a concentration of 1.33 × 10^–3 mol/L under the action of UV radiation of a 253.7 nm mercury lamp, hydroxyl radicals generated by cold plasma of a corona electric discharge, and hydroperoxyl radicals formed in water under the action of pulsed radiation of a hot plasma was studied. The degradation product identified by the fluorescence method is tyrosine. The quantum yields of phenylalanine degradation and tyrosine formation in solutions saturated and depleted in atmospheric oxygen were determined. Possible reaction mechanisms were considered.

The paper proposes a mechanism for radiation-initiated polymerization (telomerization) of perfluoroethylene in a solution of perfluorinated compounds carbogal (C₈F₁₆) or freon 350 (C₇F₁₄), which are also reaction initiators. In order to determine the possible pathways of carbogal decomposition under the influence of radiation, all bonds in it were estimated in two ways: by using thermodynamic parameters (bond strengths) of various fluoroalkanes and using quantum-chemical calculations. It was shown that, first of all, in the carbogal molecule, the C─C bonds of trifluoromethyl substituents with the cycle are destroyed, as the weakest. The resulting radicals C^●F₃ and [cyclo-(C₇F₁₃)]^● participate in the initiation reaction and the chain termination reaction. The main product of the reaction is the telomer F₃C(C₂F₄)_nC₇F₁₃, the end links of which are fluorine-containing links of carbogal. Experimental and calculated by the quantum-chemical method IR spectra confirm the presence of a cycle in the telomer and the validity of the proposed telomerization mechanism.

The effect of holmium concentration on the luminescent properties of nanosized Ho_xY_1-xVO₄ powders (where x = 0, 0.05, 0.10, 0.15) synthesized by coprecipitation of yttrium vanadate under the influence of microwave radiation was established. The elemental and phase composition, average size of nanopowders (27 ± 2 nm) were determined, the incorporation of Ho³⁺ ions into the Y³⁺ ion position was confirmed. The maximum content of holmium ions (10%) was revealed, above which concentration quenching of luminescence was observed. For Ho_0.05Y_0.95VO₄, the luminescence intensity increased by 1.5 times compared to YVO₄, while a pronounced band was observed at 550 nm, corresponding to the transition ⁵F₄ /⁵S₂ → ⁵I₈.