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Enhanced Photonic Band Gaps of Periodic Dielectric Structures Composed of Double Cylindrical Rods

100%
Woźniak T., Krawczyk M., Puszkarski H.
Acta Physica Polonica A
|
2001
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vol. 99
|
issue 5
611-625
EN
On the basis of Maradudin and McGurn's model we investigate the spectral properties of a two-dimensional photonic crystal, consisting of cylindrical rods disposed periodically throughout a dielectric matrix (the crystal is limited by two surfaces perpendicular to the axes of the rods). The model is supplemented by a new structural element in the form of dielectric rods (also cylindrical in shape) disposed coaxially within the original rods. The centers of both kinds of rods overlap forming a two-dimensional rectangular lattice in the plane parallel to the surface. Thus, the object of our study is a Maradudin-McGurn's model in which the individual rods are replaced by coaxial double rods. For this modified model we search for the optimal set of structural parameter values for which the forbidden energy gaps become greatest, giving especial attention to the role played by the additional inner rods in the emergence of gaps. We arrive at the conclusion that the condition for the opening of absolutely forbidden gaps become more favourable in a photonic crystal with double rods compared with those required in a crystal with simple rods.
2
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Polymer-Oxide Composites: Toward New Optical Materials

100%
Nedilko S.
Acta Physica Polonica A
|
2018
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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.
3
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Structure and Properties of Microcrystalline Cellulose "Ceramics-Like" Composites Incorporated with LaVO₄:Sm Oxide Compound

100%
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.
4
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Production of Barite and Boroncarbide Doped Radiation Shielding Polymer Composite Panels

88%
Evcın O., Evcın A., Bezır N., Akkurt İ., Günoğlu K., Ersoy B.
Acta Physica Polonica A
|
2017
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vol. 132
|
issue 3
1145-1148
EN
Developments in nuclear technology in the last century have lead to the use of radiation in different areas of human activity. These are not just the energetics but also food, agriculture, medicine, industry and science. Thus, radiation has become an inevitable phenomenon in our lives. Since we cannot isolate radiation from our life, the radiation protection methods should be available. As alternatives to conventional radiation prevention methods, such as lead and heavy concrete shielding, more functional materials need to become the focus of research. The development of the least harmful to the environment, easily applicable, flexible radiation shields has become very important. In this study, silicon matrix composite panels, doped with different ratios of barite and boron carbide, were produced and characterized by optical and scanning electron microscopy (SEM). Gamma and neutron radiation shielding properties of these materials were investigated. The results have been compared with the lead as the standard shielding material.
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