Zinātniskie raksti (CFI) / Scientific articles

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Browsing Zinātniskie raksti (CFI) / Scientific articles by Author "Akilbekov, Abdirash T."

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    Ab initio calculations of pure and Co+2-doped MgF2 crystals
    (Elsevier B.V., 2020) Usseinov, Abay; Gryaznov, Denis; Popov, Anatoli; Kotomin, Eugene A.; Seitov, D. D.; Abuova, Fatima; Nekrasov, Kirill A.; Akilbekov, Abdirash T.
    Ab initio calculations of the atomic, electronic and vibrational structure of a pure and Co+2 doped MgF2 crystals were performed and discussed. We demonstrate that Co+2 (3d7) ions substituting for Mg is in the high spin state. In particular, the role of exact non-local exchange is emphasized for a proper reproduction of not only the band gap but also other MgF2 bulk properties. It allows us for reliable estimate of the dopant energy levels position in the band gap, and its comparison with the experimental data. Thus, the present ab initio calculations and experiment data demonstrate that the Co+2 ground state level lies at ≈2 eV above the valence band top.
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    Depth profiles of aggregate centers and nanodefects in LiF crystals irradiated with 34 MeV 84Kr, 56 MeV 40Ar and 12 MeV 12C ions
    (Elsevier B.V., 2018) Dauletbekova, Alma K.; Skuratov, Vladimir Alexeevich; Kirilkin, N. S.; Manika, Ilze P.; Maniks, Janis J.; Zabels, Roberts; Akilbekov, Abdirash T.; Volkov, Alexander E.; Baizhumanov, Muratbek K.; Zdorovets., Maxim V; Seitbayev, Aibek
    Depth profiles of nanohardness and photoluminescence of F2 and F3 + centers in LiF crystals irradiated with 12 MeV 12C, 56 MeV 40Ar and 34 MeV 84Kr ions at fluences 1010–1015 ions/cm2 have been studied using laser scanning confocal microscopy, dislocation etching and nanoindentation techniques. The room temperature irradiation experiments were performed at DC-60 cyclotron (Astana, Kazakhstan). It was found that the luminescence intensity profiles of aggregate color centers at low ion fluences correlate with electronic stopping profiles. The maximum intensity of aggregate center luminescence is observed at fluence around 1013 ions/cm2 and rapidly decreases with further increase of fluence. At the highest ion fluences, the luminescence signal is registered in the end-of-range area only. The depth profiles of nanohardness and chemical etching have shown remarkable ion-induced formation of dislocations and increase of hardness which in the major part of the ion range correlate with the depth profile of electronic energy loss. An exception is the end-of-range region where strong contribution of nuclear energy loss to hardening at high fluences is observed.
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    Ion track template technique for fabrication of ZnSe2O5 nanocrystals
    (Elsevier B.V., 2020) Akilbekov, Abdirash T.; Akylbekova, Aiman; Usseinov, Abay; Kozlovskiy, A. L.; Baymukhanov, Z.; Giniyatova, Sh G.; Popov, Anatoli I.; Dauletbekova, Alma
    ZnSe2O5 nanocrystals with an orthorhombic structure were synthesized by electrochemical deposition into a-SiO2/n-Si ion track template formed by 200 MeV Xe ion irradiation with the fluence of 107 ions/cm2. The lattice parameters determined by the X-ray diffraction and calculated by the CRYSTAL computer program package are very close to each other. It was shown that ZnSe2O5 has a direct band gap of 2.8 eV at the Γ-point. In addition, the calculated charge distribution and chemical bonds show that the crystal has an ion-covalent nature. The photoluminescence excited by photons at 300 nm has a low intensity arising mainly due to zinc and oxygen vacancies.
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    Ion-Track Template Synthesis and Characterization of ZnSeO3 Nanocrystals
    (MDPI, 2022) Dauletbekova, Alma; Akylbekova, Aiman; Sarsekhan, Gulnaz; Usseinov, Abay; Baimukhanov, Zein; Kozlovskiy, Artem; Vlasukova, Liudmila A.; Komarov, Fadey F.; Popov, Anatoli i.; Akilbekov, Abdirash T.
    ZnSeO3 nanocrystals with an orthorhombic structure were synthesized by electrochemical and chemical deposition into SiO2/Si ion-track template formed by 200 MeV Xe ion irradiation with the fluence of 107 ions/cm2 . The lattice parameters determined by the X-ray diffraction and calculated by the CRYSTAL computer program package are very close to each other. It was found that ZnSeO3 has a direct band gap of 3.8 eV at the Γ-point. The photoluminescence excited by photons at 300 nm has a low intensity, arising mainly due to zinc and oxygen vacancies. Photoluminescence excited by photons with a wavelength of 300 nm has a very low intensity, presumably due to electronic transitions of zinc and oxygen vacancies. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
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    Paramagnetic Defects and Thermoluminescence in Irradiated Nanostructured Monoclinic Zirconium Dioxide
    (MDPI, 2022) Ananchenko, Daria V.; Nikiforov, Sergey V.; Sobyanin, Konstantin V.; Konev, Sergey F.; Dauletbekova, Alma K.; Akhmetova-Abdik, Gulzhanat; Akilbekov, Abdirash T.; Popov, Anatoli I.
    The ESR spectra of nanostructured samples of monoclinic ZrO2 irradiated by electrons with energies of 130 keV, 10 MeV, and by a beam of Xe ions (220 MeV) have been studied. It has been established that irradiation of samples with electrons (10 MeV) and ions leads to the formation of radiation-induced F+ centers in them. Thermal destruction of these centers is observed in the temperature range of 375–550 K for electron-irradiated and 500–700 K for ion-irradiated samples. It is shown that the decrease in the concentration of F+ centers is associated with the emptying of traps responsible for thermoluminescence (TL) peaks in the specified temperature range. In the samples irradiated with an ion beam, previously unidentified paramagnetic centers with g = 1.963 and 1.986 were found, the formation of which is likely to involve Zr3+ ions and oxygen vacancies. Thermal destruction of these centers occurs in the temperature range from 500 to 873 K. © 2022 by the authors. --//-- This is an open access article Ananchenko D.V., Nikiforov S.V., Sobyanin K.V., Konev S.F., Dauletbekova A.K., Akhmetova-Abdik G., Akilbekov A.T., Popov A.I., "Paramagnetic Defects and Thermoluminescence in Irradiated Nanostructured Monoclinic Zirconium Dioxide", (2022) Materials, 15 (23), art. no. 8624, DOI: 10.3390/ma15238624 published under the CC BY 4.0 licence.