9 results on '"Vladimir G. Zubkov"'
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2. Structural and spectroscopic characterization of a new series of Ba2RE2Ge4O13(RE = Pr, Nd, Gd, and Dy) and Ba2Gd2−xEuxGe4O13tetragermanates
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Vladimir G. Zubkov, Yana V. Baklanova, Leonid Yu. Mironov, Olga A. Lipina, Alexander P. Tyutyunnik, Anastasia V. Chvanova, Ksenia G. Belova, Ludmila L. Surat, Andrey N. Enyashin, and Alexander Yu. Chufarov more...
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Materials science ,Phosphor ,02 engineering and technology ,Crystal structure ,Nitride ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Crystallography ,Quantum efficiency ,Chemical stability ,0210 nano-technology ,Powder diffraction ,Monoclinic crystal system ,Solid solution - Abstract
A new series of Ba2RE2Ge4O13 (RE = Pr, Nd, Gd, Dy) germanates and Ba2Gd2−xEuxGe4O13 (x = 0.1–0.8) solid solutions have been synthesized using the solid-state reaction technique and characterized by X-ray powder diffraction. All compounds crystallize in the monoclinic system, space group C2/c, Z = 4. The crystal lattice consists of RE2O12 dimers, zigzag C2-symmetric [Ge4O13]10− tetramers, and ten-coordinated Ba atoms located in voids between polyhedra. The density-functional theory (DFT) calculations performed on a rich set of Ba2RE2Ge4O13 compounds have confirmed the high thermodynamic stability of monoclinic modification. Under ultraviolet (UV) light excitation Ba2Gd2−xEuxGe4O13 phosphors exhibit an orange-red emission corresponding to the characteristic f–f transitions in Eu3+ ions. The highest intensity of lines at 580 nm (5D0 → 7F0), 582–602 nm (5D0 → 7F1), 602–640 nm (5D0 → 7F2), 648–660 nm (5D0 → 7F3), and 680–715 nm (5D0 → 7F4) is observed for the samples with x = 0.4–0.6. The possibility of their application has been assessed by studying their color characteristics, quantum efficiency, and thermal stability. The obtained data indicate that Ba2Gd2−xEuxGe4O13 solids can be considered as promising materials for UV-excited phosphor-converted light-emitting diodes (LEDs) if an aluminum nitride substrate (λex = 255 nm) is used as a semiconductor chip. more...
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- 2021
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Catalog
3. On the energy transfer in LiMgPO4 doped with rare-earth elements
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D. A. Akulov, Vladimir G. Zubkov, M. V. Kuznetsov, A. I. Surdo, M. O. Kalinkin, R. M. Abashev, Dina G. Kellerman, and N. I. Medvedeva
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Photoluminescence ,Materials science ,Ab initio quantum chemistry methods ,Solid-state reaction route ,Doping ,Materials Chemistry ,Physical chemistry ,Orthorhombic crystal system ,General Chemistry ,Radioluminescence ,Thermoluminescence ,Spectral line - Abstract
The phosphates LiMgPO4:RE (RE – Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm) with an olivine-type orthorhombic structure were synthesized by the conventional solid state reaction route and their optical properties were examined by the experimental and theoretical methods. In this work, we showed that the radioluminescence and thermoluminescence spectra of irradiated LiMgPO4:RE (RE = Sm, Gd, Tb, Dy, Tm) consist of lines reflecting 4f–4f transitions in the rare-earth element. For LiMgPO4:RE (RE = Nd, Ho, Er), they coincide with the spectrum of the phosphate matrix with two broad bands at 360 nm and 650 nm but are much more intense. A model of energy transfer is proposed to explain this phenomenon. It is shown that the model is confirmed by the features of photoluminescence in doped LiMgPO4 and by the results of ab initio calculations. more...
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- 2021
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4. Crystal structure, luminescence properties and thermal stability of BaY2−xEuxGe3O10 phosphors with high colour purity for blue-excited pc-LEDs
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Leonid Yu. Mironov, Alexander Yu. Chufarov, Ludmila L. Surat, Alexander P. Tyutyunnik, Yana V. Baklanova, Andrey N. Enyashin, Olga A. Lipina, and Vladimir G. Zubkov
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Analytical chemistry ,chemistry.chemical_element ,Phosphor ,General Chemistry ,Crystal structure ,Catalysis ,chemistry ,Excited state ,Materials Chemistry ,Thermal stability ,Quantum efficiency ,Luminescence ,Europium ,Monoclinic crystal system - Abstract
A new series of BaY2−xEuxGe3O10 (x = 0.1–0.8) trigermanates has been synthesized using the solid-state reaction method. A powder XRD study has revealed that the compounds crystallize in the monoclinic system, space group P21/m, Z = 2. The crystal lattice consists of distorted Y/EuO6 octahedra, trigermanate [Ge3O10]8− groups and Ba atoms located in eight-fold coordinated irregular sites. Under UV and 465 nm light excitation, the samples exhibit reddish-orange emission corresponding to the characteristic 5D0 → 7FJ transitions in Eu3+ ions. Concentration dependence study has shown that the powders with europium content x = 0.4–0.6 possess the highest luminescence intensity under 393 nm and 465 nm excitation. It has also been revealed that the predominant mechanism causing concentration quenching in the BaY2−xEuxGe3O10 series is due to multipolar interactions. The investigations on colour characteristics, quantum efficiency and thermal stability performance of BaY2−xEuxGe3O10 phosphors were carried out for the feasibility study of their practical application. The results indicate that BaY2−xEuxGe3O10 can be considered as a promising material for blue-excited phosphor-converted LEDs. more...
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- 2020
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5. Structural, electronic, and optical studies of BaRE2Ge3O10 (RE = Y, Sc, Gd–Lu) germanates with a special focus on the [Ge3O10]8− geometry
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Alexander Yu. Chufarov, Yana V. Baklanova, Ksenia G. Belova, Alexander P. Tyutyunnik, Olga A. Lipina, Inna V. Baklanova, Vladimir G. Zubkov, Andrey N. Enyashin, and Ludmila L. Surat
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Lanthanide ,Materials science ,Photoluminescence ,Infrared spectroscopy ,Geometry ,02 engineering and technology ,General Chemistry ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Ion ,Octahedron ,General Materials Science ,Diffuse reflection ,0210 nano-technology ,Monoclinic crystal system - Abstract
A new series of BaRE2Ge3O10 (RE = Y, Sc, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) trigermanates has been prepared using a solid-state reaction. Powder XRD study has revealed that the compounds crystallize in the monoclinic system, space group P21/m, Z = 2. The crystal lattice consists of edge-sharing REO6 octahedra, bowed trigermanate [Ge3O10]8− groups, and Ba atoms located in eight-fold coordinated irregular sites. The geometry of [Ge3O10]8− anions persisting within different trigermanates has been examined with a special focus on the values of Ge–Ge–Ge angles and the types of conformation between the central and terminal GeO4 tetrahedra. The arrangement of [Ge3O10]8− anions in BaRE2Ge3O10 (RE = Y, Sc, Gd–Lu) crystal lattices is found to be unique. DFT calculations of different polymorphs for BaY2Ge3O10 and BaLa2Ge3O10 compounds have confirmed that our fabrication protocol yields all the products in their most thermodynamically stable forms. According to the results of vibrational spectroscopy studies, diffuse reflectance and photoluminescence measurements, the BaRE2Ge3O10 trigermanates are promising compounds for the preparation of efficient lanthanide ion activated phosphors. more...
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- 2019
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6. Synthesis, crystal structure and optical properties of Me(OH)(HCOO)2 (Me = Al, Ga)
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I. F. Berger, Vladimir N. Krasil’nikov, Andrei N. Enyashin, Alexander P. Tyutyunnik, Vladimir G. Zubkov, and Inna V. Baklanova
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Materials science ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Crystallography ,chemistry.chemical_compound ,chemistry ,Aluminium ,Hydroxide ,General Materials Science ,Emission spectrum ,Gallium ,0210 nano-technology ,Luminescence ,Excitation ,Monoclinic crystal system - Abstract
The formation conditions, crystal structure and luminescence properties of aluminum and gallium hydroxide diformates, Me(OH)(HCOO)2, have been established. Both compounds crystallize in a monoclinic lattice (space group C2, #5 and Z = 8) with parameters: a = 8.8629(2) A, b = 9.9890(2) A, c = 10.2411(1) A, β = 106.223(1)°, and V = 870.56(3) A3 (Al) and a = 8.8746(1) A, b = 10.3291(1) A, c = 10.27870(9) A, β = 105.7565(6)°, and V = 906.81(2) A3 (Ga). The emission spectra of Me(OH)(HCOO)2 under UV excitation with wavelength λ = 285 nm exhibit maxima in the range of 440–470 nm. The emission accompanied by light-blue luminescence is greatly enhanced when going from the aluminum to the gallium compound. The origin of intrinsic emission centers responsible for the luminescence properties of Me(OH)(HCOO)2 is suggested and the higher emission of the gallium hydroxide diformate is substantiated by means of density-functional theory calculations. more...
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- 2018
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7. Nd3+,Ho3+-Codoped apatite-related NaLa9(GeO4)6O2 phosphors for the near- and middle-infrared region
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A. Dominic Fortes, Nadezda V. Tarakina, Alexander P. Tyutyunnik, Olga A. Lipina, Andrey N. Enyashin, Ludmila L. Surat, Alexander Yu. Chufarov, Vladimir G. Zubkov, Evgeny V. Gorbatov, and Yana V. Baklanova more...
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010302 applied physics ,Materials science ,Rietveld refinement ,Analytical chemistry ,chemistry.chemical_element ,Phosphor ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Neodymium ,Photon upconversion ,Inorganic Chemistry ,chemistry ,Excited state ,0103 physical sciences ,Germanate ,0210 nano-technology ,Luminescence ,Holmium - Abstract
The apatite-like NaLa9(GeO4)6O2:Nd3+,Ho3+ phosphor is prepared using the solid-state method. Rietveld refinement of high-resolution time-of-flight neutron powder diffraction measurements indicate that this compound crystallizes in the hexagonal system with space group P63/m, Z = 1 and unit cell parameters a = 9.88903(6) A, c = 7.25602(5) A, V = 614.521(7) A3 at room temperature. The 4f sites are statistically occupied by La, Nd and Na, while 6h sites are occupied by La and Nd. Luminescence in the near- and middle-IR range caused by the transitions in neodymium and holmium ions is excited under 808 nm laser diode radiation. The highest emission intensity in NaLa9-x-yNdxHoy(GeO4)6O2 is attained at trace amounts of holmium, and it decreases sharply when y increases to 0.01. The IR phosphors have a good thermal stability and exhibit a very weak upconversion emission in the red spectral range upon 808 nm excitation. A scheme of excitation and emission pathways involving ground/excited state absorption, energy transfer, cross-relaxation, nonradiative multiphonon relaxation processes in Nd3+ and Ho3+ ions has been proposed. The data analysis indicates that Nd3+ ions serve as sensitizers for Ho3+ ions in these compounds, stimulating intense 2.1 μm and 2.7 μm emissions. These apatite-related germanate phosphors are promising materials for near- and middle-infrared solid-state lighting applications. more...
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- 2018
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8. Structure, magnetic and optical properties of Sr3RE2(Ge3O9)2 cyclogermanates (RE = La–Gd)
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Olga A. Lipina, Alexander P. Tyutyunnik, Dina G. Kellerman, Yana V. Baklanova, Alexander Yu. Chufarov, Vladimir G. Zubkov, M. A. Melkozerova, Andrey N. Enyashin, and Ludmila L. Surat
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Phase transition ,Materials science ,Photoluminescence ,Band gap ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Magnetic susceptibility ,0104 chemical sciences ,Ion ,Crystallography ,Lattice (order) ,General Materials Science ,Density functional theory ,0210 nano-technology ,Monoclinic crystal system - Abstract
A new series of Sr3RE2(Ge3O9)2 (RE = La, Pr, Nd, Sm, Eu, Gd) cyclogermanates has been prepared using an ethylenediaminetetraacetic acid assisted route. The powder XRD study reveals that the compounds crystallize in the monoclinic space group C2/c, Z = 4. A decrease in the crystal radius of RE3+ ions in Sr3RE2(Ge3O9)2 (RE = La–Gd) causes a morphotropic phase transition followed by a step-like change of the lattice parameters. The transition is accompanied by internal reorganization, including the redistribution of rare earth and strontium ions among three symmetry independent Sr/RE sites, a conformation change of [Ge3O9]6− rings and a variation of Sr/RE(2) atom coordination from seven-fold to nine-fold. Density functional theory calculations reveal that Sr3RE2(Ge3O9)2 compounds are indirect bandgap materials with a band gap around 3.0 eV. The magnetic property measurements indicate that Sr3RE2(Ge3O9)2 (RE = Pr, Sm, Gd) are Curie–Weiss paramagnets up to 2 K. For Sr3Eu2(Ge3O9)2 an anomaly of magnetic susceptibility is found at about 60 K. A photoluminescence study of the Sr3Sm2(Ge3O9)2 and Sr3Eu2(Ge3O9)2 samples reveals an emission in the visible spectral range, corresponding to the characteristic 4f–4f transitions in rare earth ions. more...
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- 2018
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9. Synthesis and structural study of a new group of trigermanates, CaRE2Ge3O10(RE = La–Yb)
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E. G. Vovkotrub, Vladimir G. Zubkov, Olga A. Lipina, Ludmila L. Surat, Alexander P. Tyutyunnik, and Ivan I. Leonidov
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Diffraction ,Chemistry ,Rietveld refinement ,Rare earth ,General Chemistry ,Condensed Matter Physics ,Metal ,Crystallography ,Group (periodic table) ,visual_art ,Site occupancy ,visual_art.visual_art_medium ,General Materials Science ,Monoclinic crystal system - Abstract
A new series of germanates CaRE2Ge3O10 (RE = Y, La–Yb) has been prepared using an EDTA-assisted route. Rietveld refinement of room temperature powder X-ray diffraction patterns shows that these compounds crystallize in the monoclinic system (S.G. P21/c, Z = 4) and have two morphotropic transitions. The calcium and rare earth atoms are distributed among three nonequivalent sites and form layers along the [0 0 1] direction connected into the framework through [Ge3O10]. The morphotropic transitions are accompanied by changes in the site occupancy factors of metal cations and by variation in the first and second coordination spheres of Ca2+/RE3+. more...
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- 2015
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