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1
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Polymer-Oxide Composites: Toward New Optical Materials

100%
Nedilko S.
Acta Physica Polonica A
|
2018
|
vol. 133
|
issue 4
829-837
EN
Brief summary concerning properties of the polymer matrix incorporated with inorganic, e.g. oxide particles, micro/nanocomposites and opportunity to use these composites as optical materials for modern optics and optoelectronic devices is presented in the work. Structure and morphology of the several sets of the new polymer micro/nanocomposites based on the microcrystalline cellulose incorporated with micro/nanoparticle of various oxides (NaNO₂, La_{1-x}Sm_{x}VO₄, La_{1-x}Eu_{x}VO₄ and K₂Eu(PO₄)(MoO₄)), were prepared by "dry" and "wet" cool pressing procedure. Morphology of these composites was described as ensemble of cellulose plates and located gains of the oxide particles. Temperature dependences of complex dielectric permittivity and luminescence properties of the composites were studied. Temperature and electromagnetic field frequency dependences of the dielectric permittivity revealed influence of oxide particles on the characteristics of the microcrystalline cellulose. Both wide band (matrix emission) and narrow lines (RE ions emission) of visible luminescence (350-750 nm range) of the composites is excited in the range 250-550 nm. The luminescence characteristics displayed effect of cellulose on the electronic system of the Sm³⁺ and Eu³⁺ ions and effect of oxide particles on the cellulose matrix was shown, too. Spectral characteristics and high intensity of luminescence showed perspectives of studied composites to be used as light converters in LED and elsewhere as optics luminescent materials.
2
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Luminescent Spectroscopy of the Yb³⁺ Ions in the PbWO₄ Crystal

63%
Chukova O., Nedilko S.
Acta Physica Polonica A
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2018
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vol. 133
|
issue 4
918-922
EN
Luminescent properties of the PbWO₄ crystals undoped and doped with the Yb³⁺ ions were studied. Emission spectra of the crystals consist of broadband matrix emission in 350-750 nm spectral range and narrow spectral lines caused by inner electron transitions in the impurity Yb³⁺ ions in 920-1040 nm spectral range. Analysis of the linear spectra has shown that Yb³⁺ ions form two types of emission centres. Structures of these centers are discussed taking into account possibility of the impurity ions incorporation in different positions (Pb and W sites) in the crystal lattice. Effects of the Yb³⁺ impurities on matrix emission were studied. Transfer of excitation energy from matrix to the Yb³⁺ decreases intensity of the red band of matrix emission. The Yb³⁺ impurities also increase intensity of the blue band by formation of additional Yb³⁺-induced channel of excitation of this band. The described effects of Yb³⁺ doping on properties of matrix emission are caused by the Yb³⁺ ions arranged in Pb positions.
3
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Ionic Conductivity in Multiphase Li₂O-7GeO₂ Compounds

39%
Nesterov O., Trubitsyn M., Nedilko S., Volnianskii M., Plyaka S., Rybak Y.
Acta Physica Polonica A
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2018
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vol. 133
|
issue 4
892-896
EN
Crystallization of Li₂O-7GeO₂ glass was carried out on heating, simultaneously differential scanning calorimetry and electric properties were studied. Morphology of the phase states obtained at glass devitrification was examined by atomic force microscopy. It was shown that amorphous phase of Li₂O-7GeO₂ was crystallized in stages through the intermediate state with increased conductivity σ . In the intermediate state the sample volume was occupied by nanometer-sized nuclei with ordered structure surrounded by internuclear amorphous medium. Complete glass crystallization occurred through transformation of nanometer-sized nuclei into micrometer-sized crystallites and was accompanied by a sharp and irreversible decrease of conductivity. Atomic force microscopy of the samples heat-treated in different ways showed that Li₂O-7GeO₂ glass crystallization was suppressed near the surface and mainly proceeded within the sample bulk. Charge transfer in amorphous, nanocrystalline intermediate and polycrystalline phases of Li₂O-7GeO₂ was associated with motion of the weakly bound Li ions.
4
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Structure and Transport Properties of La_{0.75-x}RE_xCa_{0.25}MnO_3 (RE = Gd, Dy, Ho; 0≤ x≤0.75) Manganites

39%
Drozd V., Pękała M., Kovac J., Skorvanek I., Szymański M., Nedilko S.
Acta Physica Polonica A
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2004
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vol. 106
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issue 5
751-758
EN
Structure and transport properties have been studied for a series of La_{0.75-x}RE_xCa_{0.25}MnO_3 manganites with heavy rare earth ions of Gd, Dy, Ho substituting La with x=0, 0.10, 0.25, 0.50, and 0.75. Polycrystalline samples were prepared by the carbonate precipitation route. The oxygen content was determined by the iodometric titration. The X-ray investigations carried out by the powder method show that the unit cell volume gradually decreases and orthorhombic distortion of the lattice increases with rising RE content. Below the room temperature the electrical resistivity is of the semiconducting type for all the samples studied. Electrical resistivity vs. temperature dependences were analyzed within different models: simple thermal activation, Mott's variable range hopping, adiabatic, nonadiabatic, and bipolaron. The Curie temperatures of Gd, Dy, and Ho substituted manganites determined from magnetization measurements show that at 280 K all the samples are in the paramagnetic phase. The increasing RE fraction reduces magnetization at 4 K as compared to La_{0.75}Ca_{0.25}MnO_3.
5
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Synthesis and Luminescence Properties of Pr³⁺-Doped BiPO₄ Polycrystals

39%
Chornii V., Nedilko S., Bychkov K., Terebilenko K., Slobodyanik M., Boyko V.
Acta Physica Polonica A
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2018
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vol. 133
|
issue 4
843-846
EN
The results of synthesis, crystal structure characterization and luminescence properties study of the Pr³⁺-doped bismuth orthophosphate, BiPO₄, polycrystals are reported. It was found that doping of bismuth orthophosphate with praseodymium of concentration more than 1% leads to phase transition of BiPO₄ from so-called "high-temperature monoclinic" to "low-temperature monoclinic" structure. At room temperature studied samples revealed intensive red luminescence caused by radiation electronic transitions in the Pr³⁺ ions under their intrinsic f → f excitation at ³H₄→ ³P₁+¹I₆ absorption transition. Influence of phase transformation as well as multi-phonon and cross-relaxation processes on the luminescence of the Pr³⁺-doped BiPO₄ compounds were discussed.
6
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Structure and Properties of Microcrystalline Cellulose "Ceramics-Like" Composites Incorporated with LaVO₄:Sm Oxide Compound

33%
Nedielko M., Alekseev O., Chornii V., Kovalov K., Lazarenko M., Nedilko S., Scherbatskyi V., Boyko V., Sheludko V.
Acta Physica Polonica A
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2018
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vol. 133
|
issue 4
838-842
EN
Composite samples based on microcrystalline cellulose matrix incorporated with micro/nanoparticles of La_{0.7}Sm_{0.3}VO₄ complex oxide were made by cool pressing procedure. Morphology, crystallinity and characteristic luminescence and dielectric properties of the composites were studied. Their morphology can be described as "ceramics-like" type, as it consists of cellulose plates and embedded oxide particles. Luminescence spectra of the composites covers the range of the whole visible light, 350-750 nm, and comprises both wide band and narrow lines, related with host and oxide luminescence, respectively. Temperature dependences of the dielectric permittivity of composites showed the impact of the oxide particles on the characteristics of the microcrystalline cellulose. An assumption was made that this influence can be affected via water molecules, hydroxyl groups or molecules of the ambient gases. Studied composites can be perspective luminescent materials for transformation of ultraviolet and violet radiation into green-red light.
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