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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Chen M., Xia Z., Molokeev M. S., Wang T., Liu Q.
Заглавие : Tuning of photoluminescence and local structures of substituted cations in xSr2Ca(PO4)2-(1 - x)Ca10Li(PO4)7:Eu2+ phosphors
Место публикации : Chem. Mater.: American Chemical Society, 2017. - Vol. 29, Is. 3. - P.1430-1438. - ISSN 08974756 (ISSN), DOI 10.1021/acs.chemmater.7b00006
Примечания : Cited References: 37. - The present work was supported by the National Natural Science Foundation of China (Grants 91622125 and 51572023), Natural Science Foundations of Beijing (2172036), and Fundamental Research Funds for the Central Universities (FRF-TP-15-003A2).
Ключевые слова (''Своб.индексиров.''): calcium--energy transfer--europium--light emission--lithium--luminescence--phosphors--photoionization--photoluminescence--single crystals--composition ranges--crystal-field splitting--luminescence measurements--non-linear variation--photoionization process--polyhedra distortion--rare earth doped solids--temperature dependent--solid solutions
Аннотация: Local structure modification in solid solution is an essential part of photoluminescence tuning of rare earth doped solid state phosphors. Herein we report a new solid solution phosphor of Eu2+-doped xSr2Ca(PO4)2-(1 - x)Ca10Li(PO4)7 (0 ≤ x ≤ 1), which share the same β-Ca3(PO4)2 type structure in the full composition range. Depending on the x parameter variation in xSr2Ca(PO4)2-(1 - x)Ca10Li(PO4)7:Eu2+, the vacancies generated in the M(4) site enable the nonlinear variation of cell parameters and volume, and this increases the magnitude of M(4)O6 polyhedra distortion. The local structure modulation around the Eu2+ ions causes different luminescent behaviors of the two-peak emission and induces the photoluminescence tuning. The shift of the emission peaks in the solid solution phosphors with different compositions has been discussed. It remains invariable at x ≤ 0.5, but the red-shift is observed at x 0.5 which is attributed to combined effect of the crystal field splitting, Stokes shift, and energy transfer between Eu2+ ions. The temperature-dependent luminescence measurements are also performed, and it is shown that the photoionization process is responsible for the quenching effect.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Chen M., Xia Z., Molokeev M. S., Lin C. C., Su C., Chuang Y. -C., Liu Q.
Заглавие : Probing Eu2+ luminescence from different crystallographic sites in Ca10M(PO4)7:Eu2+ (M = Li, Na, and K) with β-Ca3(PO4)2-type structure
Место публикации : Chem. Mater.: American Chemical Society, 2017. - Vol. 29, Is. 17. - P.7563-7570. - ISSN 08974756 (ISSN), DOI 10.1021/acs.chemmater.7b02724
Примечания : Cited References: 34. - The present work was supported by the National Natural Science Foundation of China (Grants 51722202, 91622125, and 51572023), Natural Science Foundations of Beijing (2172036), and Fundamental Research Funds for the Central Universities (FRF-TP-16-002A3). C.C.L. and C.C.S. acknowledge the financial support from the Ministry of Science and Technology of Taiwan (Contract No. MOST 104-2113-M-027-007-MY3), and M. Molokeev acknowledges support of the Russian Foundation for Basic Research (17-52-53031).
Ключевые слова (''Своб.индексиров.''): calcium--doping (additives)--excited states--light emission--lithium--luminescence--phosphors--photoluminescence--positive ions--rietveld refinement--single crystals--color tuning--crystallographic sites--different distributions--emission bands--local environments--long wavelength bands--luminescent centers--power diffraction data--europium
Аннотация: Eu2+ local environments in various crystallographic sites enable the different distributions of the emission and excitation energies and then realize the photoluminescence tuning of the Eu2+ doped solid state phosphors. Herein we report the Eu2+-doped Ca10M(PO4)7 (M = Li, Na, and K) phosphors with β-Ca3(PO4)2-type structure, in which there are five cation crystallographic sites, and the phosphors show a color tuning from bluish-violet to blue and yellow with the variation of M ions. The difference in decay rate monitored at selected wavelengths is related to multiple luminescent centers in Ca10M(PO4)7:Eu2+, and the occupied rates of Eu2+ in Ca(1), Ca(2), Ca(3), Na(4), and Ca(5) sites from Rietveld refinements using synchrotron power diffraction data confirm that Eu2+ enters into four cation sites except for Ca(5). Since the average bond lengths d(Ca-O) remain invariable in the Ca10M(PO4)7:Eu2+, the drastic changes of bond lengths d(M-O) and Eu2+ emission depending on the variation from Li to Na and K can provide insight into the distribution of Eu2+ ions. It is found that the emission band at 410 nm is ascribed to the occupation of Eu2+ in the Ca(1), Ca(2), and Ca(3) sites with similar local environments, while the long-wavelength band (466 or 511 nm) is attributed to Eu2+ at the M(4) site (M = Na and K). We show that the crystal-site engineering approach discussed herein can be applied to probe the luminescence of the dopants and provide a new method for photoluminescence tuning.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Dubrovskii A. A., Shaikhutdinov K. A., Popkov S. I., Gokhfeld D. M., Gokhfeld Yu. S., Petrov M. I.
Заглавие : Mechanism of the hysteretic behavior of the magnetoresistance of granular HTSCs: The universal nature of the width of the magnetoresistance hysteresis loop
Коллективы : Quantum Macrophysics of the Russian Academy of Sciences [3.4]; Krasnoyarsk Regional Science Foundation [18G011]; Foundation for Supporting National Science Projects
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2009. - Vol. 108, Is. 2. - P241-248. - ISSN 1063-7761, DOI 10.1134/S106377610902006X
Примечания : Cited References: 32. - This study was carried out under the program "Quantum Macrophysics" of the Russian Academy of Sciences and complex integration project no. 3.4 of the Siberian Branch of the Russian Academy of Sciences, and was partly supported by the Krasnoyarsk Regional Science Foundation (grant no. 18G011). D. A. B. and A. A. D. are grateful to the Foundation for Supporting National Science Projects.
Предметные рубрики: CRITICAL-CURRENT-DENSITY
HIGH-TEMPERATURE SUPERCONDUCTOR
CURRENT-VOLTAGE CHARACTERISTICS
EXTERNAL MAGNETIC-FIELD
BA-CU-O
JOSEPHSON MEDIUM
CRITICAL-STATE
FLUX
COMPOSITES
YBA2CU3O7-DELTA
Ключевые слова (''Своб.индексиров.''): barium--calcium--damping--electric resistance--high temperature superconductors--magnetic field effects--magnetic materials--magnetoelectronics--magnetoresistance--stiffness--classical systems--critical densities--experimental datum--external conditions--flux trapping--hysteretic behaviors--josephson vortices--residual resistances--transport currents--universal behaviors--y-ba-cu-o--hysteresis
Аннотация: The hysteretic behavior of the magnetoresistance R(H) of granular high-temperature superconductors (HTSCs) of the Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, and La-Sr-Cu-O classical systems is investigated for transport current densities lower and higher than the critical density (at H = 0). All systems exhibit universal behavior of the width of the magnetoresistance hysteresis loop: independence of transport current under identical external conditions. This means that flux trapping in HTSC grains is the main mechanism controlling the hysteretic behavior of the magnetoresistance of granular HTSCs, while pinning of Josephson vortices in the intragranular medium makes no appreciable contribution to the formation of magnetoresistance hysteresis (when transport current flows through the sample). Experimental data on relaxation of residual resistance after the action of a magnetic field also confirm this conclusion.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhang M., Xia Z., Molokeev M. S., Shi L., Liu Q.
Заглавие : New insight into the crystal structure of Sr4Ca(PO4)2SiO4 and the photoluminescence tuning of Sr4Ca(PO4)2SiO4:Ce3+,Na+,Eu2+ phosphors
Место публикации : J. Mater. Chem. C: Royal Society of Chemistry, 2016. - Vol. 4, Is. 38. - P.9078-9084. - ISSN 20507534 (ISSN), DOI 10.1039/c6tc03373c
Примечания : Cited References: 31
Ключевые слова (''Своб.индексиров.''): calcium--energy transfer--europium--light emission--light emitting diodes--luminescence--phosphate minerals--phosphors--photoluminescence--positive ions--rietveld refinement--tuning--chemical compositions--energy transfer mechanisms--green component--hexagonal cells--luminescence properties--single phase--solid state method--white lightemitting diodes (wleds)--crystal structure
Аннотация: A new single phase based on the substitution of a Sr cation by a Ca cation in the apatite-type Sr5(PO4)2(SiO4) has been fabricated with the nominal chemical composition of Sr4Ca(PO4)2(SiO4), which appears as a definite compound rather than a solid solution between (Sr,Ca)3(PO4)2 and (Sr,Ca)2SiO4. The crystal structure of Sr4Ca(PO4)2(SiO4) has been firstly analysed by the difference electron map, and further resolved by the Rietveld refinement, and the final composition has been determined as Sr4Ca(PO4)(2+x)(SiO4)(1-x)(OH)x (x = 0.64) with a hexagonal cell (P63/m). The Ce3+/Eu2+ codoped Sr4Ca(PO4)2SiO4 phosphors have been designed and prepared by the solid state method, and the photoluminescence tuning from blue to green upon 365 nm ultraviolet (UV) radiation can be realized, which is ascribed to the energy transfer from Ce3+ to Eu2+ ions. The luminescence properties and the energy transfer mechanism in Ce3+/Eu2+ codoped Sr4Ca(PO4)2SiO4 phosphors have been discussed, which might act as potential candidates for blue-green components in UV-pumped white light emitting diodes (WLEDs). © 2016 The Royal Society of Chemistry.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Юмашев, Владимир Витальевич, Кирик, Надежда Павловна, Шишкина, Нина Николаевна, Князев, Юрий Владимирович, Жижаев, Анатолий Михайлович, Соловьев, Леонид Александрович
Заглавие : Состав, структура и реакционная способность при восстановлении водородом композиционных материалов системы α-Fe2O3–CaFe2O4
Место публикации : Журнал СФУ. Химия. - 2019. - Т. 12, Вып. 1. - С. 54-72. - ISSN 1998-2836, DOI 10.17516/1998-2836-0108; J. Sib. Fed. Univ. Chem. - ISSN 2313-6049(eISSN)
Примечания : Библиогр.: 37
Предметные рубрики: CHEMICAL LOOPING GASIFICATION
OXYGEN CARRIER
PARTIAL OXIDATION
Аннотация: В работе изучены композиционные материалы системы α-Fe2O3-CaFe2O4, полученные методом высокотемпературного твердофазного синтеза из оксидов Са и Fe(III) с вариацией мольного отношения СаО/Fe2O3 от 0.15 до 1.00. Материалы охарактеризованы методами рентгеновской дифракции (РФА), сканирующей электронной микроскопии с системой энергодисперсионного микроанализа (СЭМ-ЭДС) и синхронного термического анализа (СТА) в режиме термопрограммируемого восстановления водородом (H2-ТПВ). СЭМ-ЭДС - исследование образцов выявило формирование сложной микроструктуры материала по типу «ядро-оболочка» с фазой гематита в качестве «ядра». H2-ТПВ образцов позволило установить, что с увеличением содержания фазы CaFe2O4 (от 33.4 до 97.5 мас. %) наблюдается снижение вклада низкотемпературных форм решеточного кислорода в областях 350-510 °С (до 2.6 раза) и 510-650 °С (до 1.7 раза) и рост вклада высокотемпературной формы кислорода в интервале 650-900 °С (до 2 раз). На основе оценки подвижности решеточного кислорода высказано предположение о перспективности использования полученных композиционных материалов с содержанием фазы CaFe2O4 более 55.2 мас. % в качестве носителей кислорода в химических циклических процессах получения синтез-газа.In this paper, α-Fe2O3–CaFe2O4 composite materials obtained by high-temperature solid-phase synthesis from Ca and Fe (III) oxides with varying molar ratio CaO/Fe2O3 in the range 0.15-1.00 were investigated. The materials are characterized by Х-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDS) and simultaneous thermal analysis (STA) in the hydrogen temperature-programmed reduction mode (H2-TPR). SEM-EDS studies of the specimens were revealed a formation of the “core-shell” type complex microstructure of material with the hematite phase as the “core”. H2-TPR of the specimens allowed to establish a decrease of the contribution of low-temperature forms of lattice oxygen in areas of 350-510 °С (up to 2.6 times) and 510-650 °С (up to 1.7 times), and the growth of the contribution of the high-temperature oxygen form in the range of 650-900 °С (up to 2 times) with an increase in the content of the phase CaFe2O4 from 33.4 to 97.5 wt. %. Relying on the assessment of lattice oxygen mobility, it was suggested, that the samples with content of CaFe2O4 phase more than 55.4 wt. % are promising for use as oxygen carriers in chemical looping processes of syngas production.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Denisova L. T., Molokeev M. S., Galiakhmetova N. A., Denisov V. M., Belousova N. V.
Заглавие : Heat capacity and thermodynamic properties of germanates CaR2Ge3O10 (R = Pr, Nd) in the region of 320–1000 K
Место публикации : Russ. J. Phys. Chem. A. - 2022. - Vol. 96, Is. 5. - P.913-917. - ISSN 00360244 (ISSN), DOI 10.1134/S0036024422050077
Примечания : Cited References: 30. - The authors are grateful to the Krasnoyarsk Regional Shared Resource Center of the Krasnoyarsk Science Center. This work was performed as part of a State Task for Siberian Federal University, project no. FSRZ-2020-0013
Аннотация: Sequential annealing of stoichiometric mixtures of CaCO3, Pr6O11(Nd2O3), and GeO2 in air at 1423–1473 K yields germanates CaPr2Ge3O10 and CaNd2Ge3O10. Their crystal structure is refined via X-ray diffraction. The high-temperature heat capacity (320–1000 K) is measured by means of differential scanning calorimetry. The thermodynamic properties of germanates are calculated using experimental dependences Cp = f(T).
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Denisova L. T., Molokeev M. S., Kargin Y. F., Galiakhmetova N. A., Beletskii V. V., Denisov V. M.
Заглавие : High-temperature heat capacity and thermodynamic properties of the CaY2Ge3O10 and CaY2Ge4O12 germanates
Место публикации : Inorg. Mater. - 2022. - Vol. 58, Is. 4. - P.414-419. - ISSN 00201685 (ISSN), DOI 10.1134/S0020168522040033
Примечания : Cited References: 31. - This work was supported in part by the Russian Federation Ministry of Science and Higher Education as part of the state research target for the Siberian Federal University federal state autonomous educational institution of higher education, project no. FSRZ-2020-0013
Аннотация: The CaY2Ge3O10 and CaY2Ge4O12 germanates have been synthesized by a standard ceramic processing route using CaCO3, Y2O3, and GeO2 as starting materials, and their crystal structure has been refined by X-ray diffraction. The high-temperature (350–1000 K) experimental heat capacity data obtained for the germanates by differential scanning calorimetry have been used to calculate their principal thermodynamic functions.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shtarev D. S., Ryabchuk V. K., Rudakova A. V., Shtareva A. V., Molokeev M. S., Kirichenko E. A., Serpone N.
Заглавие : Phenomenological rule from correlations of conduction/valence band energies and bandgap energies in semiconductor photocatalysts: calcium bismuthates versus strontium bismuthates
Коллективы : Russian Science FoundationRussian Science Foundation (RSF) [19-73-10013]; Saint-Petersburg State University [39054581]
Место публикации : ChemCatChem. - 2020. - Vol. 12, Is. 6. - P.1551-1555. - ISSN 1867-3880, DOI 10.1002/cctc.201902236. - ISSN 1867-3899(eISSN)
Примечания : Cited References: 13. - The research was supported from a grant from the Russian Science Foundation (project No. 19-73-10013). We are very grateful to the staff of the Khabarovsk Innovation and Analytical Center of the Yu. A. Kosygin Institute of Tectonics and Geophysics FEB RAS, and of the Research Center on Nanophotonics and the Center for Physical Methods of Surface Investigation (to Dr. Alexandra Koroleva) of the Research Park at Saint-Petersburg State University for their valuable assistance in carrying out the research and in providing the needed equipment. VKR and AVR acknowledge financial support from a grant by the Saint-Petersburg State University (Pure ID 39054581). One of us (NS) thanks Prof. A. Albini and the staff of the PhotoGreen Laboratory of the University of Pavia for their continued hospitality
Предметные рубрики: STRUCTURAL-PROPERTIES
Аннотация: A number of calcium bismuthates were synthesized (25 to 50 mol% in Ca) and characterized by XRD, SEM, EDX, XPS and DRS techniques; the latter provided an estimate of the bandgap energies (Ebg=2.41 to 3.29 eV) via Tauc plots for indirect transitions, whereas XPS established the potentials (vs NHE) of their respective valence bands (and thus the conduction bands). Linear correlations existed between EVB/ECB and Ebg that when compared with those of strontium bismuthates (reported earlier) showed that differences in energies at Ebg=0 eV are related to the difference in the absolute electronegativities of Ca and Sr, from which the following empirical phenomenological rule is postulated: replacing one alkaline earth metal in bismuthates by another causes the points of intersection of the linear correlations ECB(Ebg) and EVB(Ebg) to be displaced by an amount equal to twice the difference in absolute electronegativities of these metals.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Novikova, Galina, V, Tsyplenkova, Darya, I, Kuzubov A. A., Kolenchukova, Oksana A., Samoilo, Alexander S., Vorobyev, Sergey A.
Заглавие : Complex of Ca(II) with ceftriaxone: Synthesis, structure, spectral and antibacterial properties
Коллективы : RFBR, Krasnoyarsk Territory; Krasnoyarsk Regional Fund of Science [20-43-240007]
Место публикации : J. Sib. Fed. Univ. Chem. - 2021. - Vol. 14, Is. 3. - P.290-301. - ISSN 1998-2836, DOI 10.17516/1998-2836-0238; Журн. СФУ. Химия. - ISSN 2313-6049(eISSN)
Примечания : Cited References: 39. - The research was funded by RFBR, Krasnoyarsk Territory and Krasnoyarsk Regional Fund of Science, project number 20-43-240007
Предметные рубрики: BASIS-SETS
ALGORITHM
1ST-ROW
CALCIUM
Аннотация: The calcium complex of ceftriaxone was synthesized and characterized by elemental, atomic-emission analysis, TGA, IR spectroscopy and density functional theory calculations. The luminescence and antibacterial properties of the ceftriaxone disodium and calcium complex wcrc investigated. Ca(II) complex was obtained in a crystalline form, cell parameters of the compound were determined. Ceftriaxone was coordinated to the calcium ion by the oxygen of the triazine cycle in the 6th position, the nitrogen of the amine group of the thiazole ring, and the oxygens of the lactam carbonyl and carboxylate groups. The complex of Ca(II) with ceftriaxone was screened for antibacterial activity against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, and the results were compared with the activity of ceftriaxone disodium salt.Кальциевый комплекс цефтриаксона был синтезирован и охарактеризован с помощью элементного, атомно-эмиссионного анализа, ТГА, ИК‑спектроскопии и расчетов теории функционала плотности. Исследованы люминесцентные и антибактериальные свойства динатриевой соли цефтриаксона и комплекса цефтриаксона с кальцием. Комплекс Ca(II) получен в кристаллическом виде, определены параметры кристаллической решетки соединения. Цефтриаксон координировался к иону кальция через атом кислорода триазинового цикла в 6-м положении, атом азота аминогруппы тиазольного кольца и атомами кислорода карбонильной и карбоксилатной групп. Комплекс Са(II) с цефтриаксоном обладает антибактериальной активностью против Staphylococcus aureus, Escherichia coli и Pseudomonas aeruginosa, полученные результаты сравнивали с активностью динатриевой соли цефтриаксона.
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10.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Golovnev N. N., Molokeev M. S., Vereschagin S. N., Atuchin V. V.
Заглавие : 2-Thiobarbiturate complexes of Ca(II): synthesis, crystal structure and thermal properties
Коллективы : International Conference on the Advancement of Materials and Nanotechnology (3; 2013 ; Nov. ; 19-22; Penang, Malaysia)
Место публикации : 3 Int. Conf. on the Advancement of Mater. and Nanotechn. (ICAMN 2013): Programme and abstracts book. - 2013. - P.157
Ключевые слова (''Своб.индексиров.''): calcium--2-thiobarbituric acid--crystal structure--thermal decomposition--ir spectroscopy
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