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Now showing items 17 - 32 of 6688

  • Near infrared luminescence of bismuth-doped MO-B2O3(M=Ca, Sr, Ba) glasses

    Liu, Junfang   Zhu, Jiqian   Yu, Haohai  

    Bi-doped MO-B2O3 (M=Ca, Sr, Ba) glasses were prepared by melting method. Excitation spectra, visible and infrared luminescence spectra were measured. Near infrared (NIR) emissions located at about 1190 nm with FWHM only 40 nm and at 1300 nm with FWHM about 200 nm can be observed in different samples when excited by 808 nm LD excitation. The two emission bands have different excitation bands. Red emission centered at 660 nm related to Bi2+ can be observed in some samples. The NIR emission at 1300 nm band disappears with the increase of optical basicity, while that of the NIR emission at 1190 nm band shows a contrary tendency. We proposed that the NIR emissions located at 1190 nm and 1300 nm originated from different bismuth centers. The infrared emission peak at about 1300 nm derives from low valence Bi ions according to the Duffy’s theory of optical basicity.
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  • Luminescence properties of M3(VO4)2:Eu3+(M?=?Ca, Sr, Ba) phosphors

    Mi, Xiaoyun   Shi, Hui   Wang, Zan   Xie, Lingjie   Zhou, Hongyan   Su, Jiangang   Lin, Jun  

    In this paper, M3(VO4)2:Eu3+(M = Ca, Sr, Ba) phosphors have been synthesized by high-temperature solid-state method. The phase composition and luminescence properties of the synthesized phosphors were characterized by X-ray powder diffraction and photoluminescence (PL) spectra, respectively. The influences of fluxing agent and doped concentration of rare-earth ions on PL properties of the phosphor were investigated. The results indicated that the energy transfers between VO4 3− and Eu3+ in the host occurred mainly via a dipole–dipole interaction mechanism. The increase in cation radius (from Ca2+ to Ba2+) in the host causes the emission peak originated from 5D0 → 7F2 transition of Eu3+ shifting from 615 to 621 nm, as well as decreasing the fluorescence lifetimes of Eu3+ from 0.77 to 0.19 ms and changing the CIE chromaticity coordinates from the orange-red region to the white region. Moreover, the emission colors of Ba3−x (VO4)2:xEu3+ can be firstly adjusted from cyan region to white light region via controlling the concentration of Eu3+. Temperature-dependent luminescence spectra proved the good thermal stability of the as-prepared phosphor. This work shows the potential application of europium-doped samples in UV converted pc-WLEDs.
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  • The Periodate-Based Double Perovskites M2NaIO6 (M = Ca, Sr, and Ba)

    Kubel, Frank   Wandl, Nicole   Pantazi, Mariana   D'Anna, Vincenza   Hagemann, Hans  

    The crystal structures of the M2NaIO6 series (M = Ca, Sr, Ba), prepared at 650 degrees C by ceramic methods, were determined from conventional laboratory X-ray powder diffraction data. Synthesis and crystal growth were made by oxidizing I with O2(air) to I7+ followed by crystal growth in the presence of NaF as mineralizator, or by the reaction of the alkali-metal periodate with the alkaline-earth metal hydroxide. All three compounds are insoluble and stable in water. The barium compound crystallizes in the cubic space group Fm3m (no. 225) with lattice parameters of a = 8.3384(1) angstrom, whereas the strontium and calcium compounds crystallize in the monoclinic space group P21/c (no. 14) with a = 5.7600(1) angstrom, b = 5.7759(1) angstrom, c = 9.9742(1) angstrom, = 125.362(1)degrees and a = 5.5376(1) angstrom, b = 5.7911(1) angstrom, c = 9.6055(1) angstrom, = 124.300(1)degrees, respectively. The crystal structure consists of either symmetric (for Ba) or distorted (for Sr and Ca) perovskite superstructures. Ba2NaIO6 contains the first perfectly octahedral [IO6]5 unit reported. The compounds of the ortho-periodates are stable up to 800 degrees C. Spectroscopic measurements as well as DFT calculations show a reasonable agreement between calculated and observed IR- and Raman-active vibrations.
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  • Proton transport properties of La0.9M0.1YbO3-delta (M = Ba, Sr, Ca, Mg)

    Okuyama, Yuji   Kozai, Takeshi   Sakai, Takaaki   Matsuka, Maki   Matsumoto, Hiroshige  

    The proton transport properties of La0.9M0.1YbO3-delta (M = Ba, Sr, Ca, Mg) were studied by the electrical conductivity measurement technique in the temperature range of 673-1173 K. The proton concentration was estimated by the weight changes due to the hydration reaction. The electrical conductivity and proton concentration of La0.9Ba0.1YbO3-delta were the highest in La0.9M0.1YbO3-delta. The electromotive force of a hydrogen gas concentration cell using La0.9Ba0.1YbO3-delta as the electrolyte was observed at 673-1073 K, and was in a good agreement with the theoretical values assuming that the proton transport number was unity. (c) 2013 Elsevier Ltd. All rights reserved.
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  • The Periodate-Based Double Perovskites M2NaIO6 (M = Ca, Sr, and Ba)

    Frank Kubel   Nicole Wandl   Mariana Pantazi   Vincenza D'Anna and Hans Hagemann  

    The crystal structures of the M2NaIO6 series (M = Ca, Sr, Ba), prepared at 650 °C by ceramic methods, were determined from conventional laboratory X-ray powder diffraction data. Synthesis and crystal growth were made by oxidizing I– with O2(air) to I7+ followed by crystal growth in the presence of NaF as mineralizator, or by the reaction of the alkali-metal periodate with the alkaline-earth metal hydroxide. All three compounds are insoluble and stable in water. The barium compound crystallizes in the cubic space group Fm3m (no. 225) with lattice parameters of a = 8.3384(1) Å, whereas the strontium and calcium compounds crystallize in the monoclinic space group P21/c (no. 14) with a = 5.7600(1) Å, b = 5.7759(1) Å, c = 9.9742(1) Å, β = 125.362(1)° and a = 5.5376(1) Å, b = 5.7911(1) Å, c = 9.6055(1) Å, β = 124.300(1)°, respectively. The crystal structure consists of either symmetric (for Ba) or distorted (for Sr and Ca) perovskite superstructures. Ba2NaIO6 contains the first perfectly octahedral [IO6]5– unit reported. The compounds of the ortho-periodates are stable up to 800 °C. Spectroscopic measurements as well as DFT calculations show a reasonable agreement between calculated and observed IR- and Raman-active vibrations.
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  • Magnetic Anomaly of La1-xMxFeO3 (M = Ca, Sr, and Ba) around 100K

    Nakamae, Yuki   Ishida, Shu   Takemura, Wataru   Ohno, Masatoshi   Okada, Akimasa   Mitsui, Toshihiro   Kobayashi, Yoshihiko   Nakamura, Jin   Asai, Kichizo  

    A magnetic anomaly has been found around 100K in La1-xMxFeO3 (M = Ca, Sr, and Ba) and Pr1-xSrxFeO3 with 0.05 <= x <= 0.4; the spontaneous magnetization of the weak ferromagnet increases below about 100K after cooling in a magnetic field. We propose a model in which Fe4+ ions populated by doped holes preferentially occupy one magnetic sublattice of the antiferromagnetic structure in LaFeO3 and PrFeO3 as a result of charge ordering, which induces an inequality between the sublattice magnetizations and modifies the system from the antiferromagnet to a ferrimagnet. The magnetization below the magnetic anomaly temperature is explained as that of a weak ferromagnet with the canted sublattice magnetizations of the ferrimagnet.
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  • Mass spectrometric decomposition of [MNO3](+) cations,where M =3D Ca,Sr,Ba

    Franski, Rafal  

    ESI-CID-MS/MS spectra of [MNO3](+) ions (M stands for Ca, Sr, Ba), the simplest ionic species composed of a metal and a nitrate group, are discussed in detail. These ions decompose through the loss of an NO molecule (with the formation of the MO2+ fragment ion) and/or the loss of an NO2 molecule (with the formation of the MO+ fragment ion). The efficiencies of these processes strongly depend on the electrostatic attraction between the metal and the oxygen atoms of the nitrate group. For the [CaNO3](+) ion the loss of an NO molecule is the only decomposition observed, for the [SrNO3](+) ion both processes are observed and their efficiencies depend on the collision energy, and for [BaNO3](+) ion the loss of an NO2 molecule is the dominant process. Alkali earth metal cations are not prone to reduction (M-II -> M-I), thus the formation of the M+ ion is a minor process. (C) 2015 Elsevier Ltd. All rights reserved.
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  • High ionic conductivity of Li3-2xMxPS4 (M =3D Ca or Mg) at high temperature

    Nguyen Huu Huy Phuc   Kazuhiro, Hikima   Hiroyuki, Muto   Atsunori, Matsuda  

    Li3-2xMxPS4 (M =3D Ca or Mg) solid electrolytes were prepared by planetary ball-milling. Solid electrolytes that were amorphous in XRD were obtained with 0 <=3D x <=3D 0.115. A new crystalline phase was detected in samples with x >=3D 0.391. The addition of Ca2+ to the Li3PS4 matrix (x <=3D 0.115) resulted in reduction of the total conductivity at room temperature but conductivity enhancement was obtained at temperatures of 50 degrees C or higher. The sample Li2.88Ca0.06PS4 exhibited conductivity of about 9 mS cm(-1) at 90 degrees C, which was much improved compared with the conductivity of intrinsic Li3PS4 (2 mS cm(-1)).
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  • Luminescent properties of Eu3+ in MWO4 (M=Ca, Sr, Ba) matrix

    Feng-wen Kang   Yi-hua Hu   Li Chen   Xiao-juan Wang   Hao-yi Wu   Zhong-fei Mu  

    The Eu3+ doped MWO4 (M=Ca, Sr, Ba) phosphors were synthesized via high temperature solid state reaction. The crystal phases of these phosphors were identified by X-ray diffraction. Shifts of the peaks in the structure were observed when Ca2+ sites in the host were completely occupied by the Sr2+ ions or Ba2+ ions. As a result of this replacement, the charge-transfer (CT) band exhibited a blue shift from CaWO4: Eu3+ to SrWO4: Eu3+ and BaWO4: Eu3+. This blue shift could be interpreted with the decreases of the bond covalence between the ligands (L) and the central ion (M) in matrix. In this work, red afterglow originated from the 5D0-7FJ (J=0,1,2,3,4) transitions of Eu3+ could clearly be observed after samples were excited at 254 nm. The thermoluminescence (TL) spectra showed that there were five traps levels in CaWO4: Eu3+ sample and two traps levels in CaWO4: Eu3+ and CaWO4: Eu3+ samples, respectively. The possible explanation of this afterglow phenomenon was also discussed in detail.
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  • Luminescent properties of Eu3+ in MWO4 (M=Ca, Sr, Ba) matrix

    Kang, Feng-wen   Hu, Yi-hua   Chen, Li   Wang, Xiao-juan   Wu, Hao-yi   Mu, Zhong-fei  

    The Eu3+ doped MWO4 (M=Ca, Sr, Ba) phosphors were synthesized via high temperature solid state reaction. The crystal phases of these phosphors were identified by X-ray diffraction. Shifts of the peaks in the structure were observed when Ca2+ sites in the host were completely occupied by the Sr2+ ions or Ba2+ ions. As a result of this replacement, the charge-transfer (CT) band exhibited a blue shift from CaWO4: Eu3+ to SrWO4: Eu3+ and BaWO4: Eu3+. This blue shift could be interpreted with the decreases of the bond covalence between the ligands (L) and the central ion (M) in matrix. In this work, red afterglow originated from the 5D0-7FJ (J=0,1,2,3,4) transitions of Eu3+ could clearly be observed after samples were excited at 254 nm. The thermoluminescence (TL) spectra showed that there were five traps levels in CaWO4: Eu3+ sample and two traps levels in CaWO4: Eu3+ and CaWO4: Eu3+ samples, respectively. The possible explanation of this afterglow phenomenon was also discussed in detail.
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  • Green-emitting (La,M,Tb)OCl (M = Mg, Ca, and Sr) phosphors

    Sun Woog Kim   Kazuya Jyoko   Toshiyuki Masui   Nobuhito Imanaka  

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  • First principle study of MF2 (M=Mg, Ca, Sr, Ba, Ra) compounds

    Jibran, M.   Murtaza, G.   Khan, M.A.   Khenata, R.   Muhmmad, S.   Ali, Roshan  

    Dialkali halides have been widely studied because of their large transparency range. The structural, elastic, electronic and optical properties of MF 2 (M = Mg, Ca, Sr, Ba, Ra) compounds in fluorite structure have been studied by using self consistent full potential linearized augmented plane wave (FLAPW) method with Wu-Cohen generalized gradient approximation (WC-GGA) and the modified Becke-Johnson potentials. Lattice constant varies inversely to bulk modulus by changing the cation from Mg to Ra in MF 2. All the compounds are found to have wide indirect band gap. Refractive index, reflectivity and optical conductivity are calculated to explain the optical nature of these compounds. [All rights reserved Elsevier].
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  • The monoclinic superstructure of the M2Pt6Al15 series (M=Ca, Sc, Y, La, Lu)

    Radzieowski, Mathis; Stegemann, Frank; Hoffmann, Rolf-Dieter; Janka, Oliver  

    The five ternary intermetallic compounds M2Pt6Al15 (M =3D Ca, Sc, Y, La, Lu) were prepared from the elements by arc-melting. The crystal structure was determined via single crystal X-ray diffraction. The title compounds crystallize in a superstructure of the RE0.67Pt2Al5 type structure (P6(3)/mmc) in the monoclinic crystal system with space group P12(1)/m1 (Sc2Pt6Al15 : a=3D 734.19(2), b =3D 1628.96(10), c =3D 734.19(2) pm, beta =3D 119.999(3)degrees; wR =3D 0.0356, 3034 F-2 values, 68 variables). The superstructure can be derived by the superspace formalism using (3 + 2)D or (3 + 1)D interpretations of the diffraction data. The structural relation to the subcell structure is discussed on the basis of a group-subgroup scheme. In the crystal structure strongly bonded [Pt2Al4](delta-) slabs are alternatingly stacked with ordered layers containing M atoms and Al-3 triangles.
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  • Optical and Electromagnetic Properties of LaCoO3:Li+;M2+(M = Ca, Sr, Ba)

    Fesich, I. V.; Trachevsky, V. V.; Dziazko, A. G.; Nedilko, S. A.; Melnik, A. K.  

    Lanthanum cobaltates modified by alkaline-earth-metal (0.10 mol%) and lithium (0.05 mol%) ions were synthesized. The samples had an orthorhombic distorted perovskite-like structure according to x-ray diffraction phase analysis. Addition of Li+ and M2+ (M = Ca, Sr, Ba) to the LaCoO3 matrix was shown to increase the unit-cell parameters, the optical band width (E-g), and the average Co oxidation state (Con+). Pure and doped LaCoO3 were characterized by the presence of paramagnetic centers as isolated structural and surface Co2+ ions and adsorption complexes [Co3 + a <-aEuro parts per thousand O (2) (-) ](center dot) on the surface of the oxide matrix at a concentration that increased in the order Ba > Sr > Ca. The cobaltates were found to possess Mott hopping conduction in the temperature range 77-298 K.
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  • Optical and Electromagnetic Properties of LaCoO3:Li+;M2+(M = Ca, Sr, Ba)

    Fesich, I. V.   Trachevsky, V. V.   Dziazko, A. G.   Nedilko, S. A.   Melnik, A. K.  

    Lanthanum cobaltates modified by alkaline-earth-metal (0.10 mol%) and lithium (0.05 mol%) ions were synthesized. The samples had an orthorhombic distorted perovskite-like structure according to x-ray diffraction phase analysis. Addition of Li+ and M2+ (M = Ca, Sr, Ba) to the LaCoO3 matrix was shown to increase the unit-cell parameters, the optical band width (E-g), and the average Co oxidation state (Con+). Pure and doped LaCoO3 were characterized by the presence of paramagnetic centers as isolated structural and surface Co2+ ions and adsorption complexes [Co3 + a <-aEuro parts per thousand O (2) (-) ](center dot) on the surface of the oxide matrix at a concentration that increased in the order Ba > Sr > Ca. The cobaltates were found to possess Mott hopping conduction in the temperature range 77-298 K.
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  • Proton transport properties of La0.9M0.1YbO3?δ (M=Ba, Sr, Ca, Mg)

    Okuyama, Yuji   Kozai, Takeshi   Sakai, Takaaki   Matsuka, Maki   Matsumoto, Hiroshige  

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