Solvothermal synthesis of well-dispersed MF2 (M = Ca, Sr, Ba) nanocrystals and their optical properties

MF2 (M = Ca, Sr, Ba) nanocrystals (NCs) were synthesized via a solvothermal process in the presence of oleic acid and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, UV/vis absorption spectra, photoluminescence (PL) excitation and emission spectra, and lifetimes, respectively. In the synthetic process, oleic acid as a surfactant played a crucial role in confining the growth and solubility of the MF2 NCs. The as-prepared CaF2, SrF2 and BaF2 NCs present morphologies of truncated octahedron, cube and sheet in a narrow distribution, respectively.

Chemical bond characteristics, thermal expansion property and compressibility of AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths)

Theoretical researches were performed on the CaFe2O4-type binary rare earth oxides AR(2)O(4) (A = Ca, Sr, Ba; R = rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations revealed that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the rare earths. In the cases of Sc and Y, both the LTEC and bulk modulus values are larger than the lanthanide series. We attribute this to the difference in the electronic configuration between Sc (Y) and lanthanide series. For SrY2O4 and BaY2O4 crystals, the theoretical values of LTEC and bulk modulus agree well with experimental ones.

Reduction of Eu3+ to Eu2+ in MAl2Si2O8 (M = Ca, Sr, Ba) in air condition

In general, the reduction of Eu3+ to Eu2+ in solids needs an annealing Process in a reducing atmosphere. in this paper, it is of great interest and importance to find that the reduction of Eu3+ to Eu2+ can be realized in a series of alkaline-earth metal aluminum silicates MAl2Si2O8 (M = Ca, Sr, Ba) just in air condition. The Eu2+-doped MAl2Si2O8 (M = Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong hand emissions of 4f(6)5d(1)-4f(7) from Eu2+ were observed at 417, 404 and 373 nm in air-annealed CaAl2Si2O8, SrAl2Si2O8 and BaAl2Si2O8, respectively, under ultraviolet excitation although the Eu3+ precursors were employed. In addition, under low-voltage electron beam excitation, Eu2+-doped MAl2Si2O8 also shows strong blue or ultraviolet emission corresponding to 4f(6)5d(1)-4f(7) transition.

Preparation and luminescent properties of rare earth ions in M2B5O9Cl : Re(M = Ca, Sr, Ba; Re=Eu, Tb)

M2B5O9X: Re(M = Ca, Sr, Ba; X = Cl, Br; Re = Eu, Th) phosphors were synthesized via solid state method. The products were characterized with X-ray powder diffraction and luminescence spectrometer. The luminescent properties as well. as the influences of the matrix composition and other doping ions on the luminescence of the rare earth ions of the co-doped phosphors were investigated. The coexistence of Eu3+, Eu2+ and Th3+ were observed in these matrices. The phenomenon may be explained by the electron transfer theory. The sensitization of Ce3+ ion improves the intensity of emission of Eu2+, and Tb3+. The competition between electron transfer among conjugate rare earth ions and energy migration might be the reasons for the observation. We predict a novel trichromatic phosphor co-doped with Eu3+ Tb3+ in M2B5O9X.

A self-consistent field theory study on the morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers

By using a combinatorial screening method based on the self-consistent field theory, we investigate the equilibrium morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers in two dimensions. The triangle phase diagrams of both block copolymers are constructed by systematically varying the volume fractions of blocks A, B, and C. In this study, the interaction energies between species A, B, and C are set to be equal. Four different equilibrium morphologies are identified, i.e., the lamellar phase (LAM), the hexagonal lattice phase (HEX), the core-shell hexagonal lattice phase (CSH), and the two interpenetrating tetragonal lattice phase (TET2). For the linear ABCBA block copolymer, the reflection symmetry is observed in the phase diagram except for some special grid points, and most of grid points are occupied by LAM morphology. However, for the H-shaped (AB)(2)C(BA)(2) block copolymer, most of the grid points in the triangle phase diagram are occupied by CSH morphology, which is ascribed to the different chain architectures of the two block copolymers. These results may help in the design of block copolymers with different microstructures.

Synthesis of nanocrystalline Ba(CoxZn1-x)(2)Fe16O27 by sol-gel auto-combustion method

The synthesis of nanocrystalline W-type hexaferrites Ba(CoxZn1-x)(2)Fe16O27 powders by sol-gel auto-combustion method has been investigated. The thermal decomposition process of dried gel was studied by thermogravimetry (TG), differential thermal analysis (DTA) and infrared spectra (IR). The structural and magnetic properties of resultant particles were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). The results reveal that the dried gel exhibits auto-combustion behavior. After combustion, pure nanocrystalline W-type hexaferrite phase starts to appear at the calcination temperature of 800 degrees C. The crystallinity and the grain size increase at higher temperature. The saturation magnetization and coercivity clearly depend on calcination temperature and Co content X.

Chemical bond properties and Mossbauer spectroscopy in (La1-xMx)(2)CuO4(M=Ba, Sr)

By using the average band-gap model, the chemical bond properties of (La1-x, M-x)(2)CuO4(M=Ba, Sr) were calculated. The calculated covalencies for Cu-O and La-O bond in the compounds are 0.3 and 0.03 respectively. Mossbauer isomer shifts of Fe-57 doped in La2CuO4 and Sn-119 doped in La2CuO4 were calculated by using the chemical surrounding factor defined by covalency and electronic polarizability. Four valence state tin and three valence iron sites were identified in Fe-57 and Sn-119 doped La2CuO4.

M_2CeO_4(M=Ca,Sr,Ba)的结构与发光特性

Sr_2CeO_4是一种新型的一维结构发光材料,其特殊的结构对其发光特性有决定性的作用。Sr2CeO4体系中可以顺利地进行能量传递,产生较强电荷迁移发光。合成了M2CeO4（M=Ca,Sr,Ba）,发现与Sr2CeO4具有类似结构的Ba2CeO4也可以发光,而结构完全发生了变化的Ca2CeO4则不发光。

ABF_3:Eu,Gd(A:K,Li;B:Ba,Mg)中Gd~(3+)→Eu~(2+)的能量传递

通过高温固相反应法,在高纯N_2气氛中合成了BaLiF_3,KMgF_3中单掺和双掺Eu,Gd的ABF_3型复合氟化物。研究了各类掺杂体系的光谱特性,观察到了Gd~(3+)→Eu~(2+)的能量传递,分析了能量传递过程,探讨了能量传递机理,并讨论了Gd~(3+)和Eu~(2+)的取代格位。

Eu~(2+):MAl_2O_4(M=Ba~(2+),Sr~(2+))的发光与晶体化学键相关性的研究

本文应用复杂晶体化学键理论对Eu~(2+):MAl_2O_4(M=Ba~(2+),Sr~(2+))晶体的化学键参数进行了计算,讨论了晶体中Eu~(2+)的发光性与其所取代离子格位的化学键性质间的关系。

M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)的真空紫外光谱特性的研究

采用高温固相反应法合成了M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)中荧光体,测量了荧光体的真空紫外激发光谱,研究了M_2B_5O_9Cl:Eu(M=Ca,Sr,Ba)的真空紫外光谱特性,观察到基质吸收带位于120～200 nm区域,Eu~(2+)离子的5d能级劈裂随着M~(2+)的半径的增加而减小,同时也观察到基质与稀土离子之间存在的能量传递。

Layered La-Ba-Cu mixed oxides with perovskite structure as catalyst for NO reduction by CO

The mixed oxides, including LaBa2Cu3O7, LaBaCu2O5, La4BaCu5O12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, H-2-TPR. It was found that their structures were layered ABO(3) perovskite structure and they were the active catalysts for the NO reduction by CO. The existence of Cu3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

Studies on the elimination of NO over the La-Ba-Cu mixed oxide catalysts with perovskite structure

The mixed oxides, including YBa2Cu3O7, LaBa2Cu3O7, LaBaCu2O5, La2BaCu3O7, La4BaCu5O12 with perovskite structure, were prepared. The catalysts were characterized by means of chemical analysis, XRD, TPD and TPR method. It was found that they were the active catalysts for the NO decomposition and NO reduction by CO. The existance of Cu3+ is an important factor to give the catalysts a high activity for the NO reduction by CO.

La-Ba-Cu复合氧化物在催化消除NO反应中催化性能的研究

合成了具有钙钛石结构的复合氧化物ＹＢａ２Ｃｕ３Ｏ７、ＬａＢａ２Ｃｕ３Ｏ７、ＬａＢａＣｕ２Ｏ５、Ｌａ２ＢａＣｕ３Ｏ７和Ｌａ４ＢａＣｕ５Ｏ１２．考察了它们对ＮＯ分解和ＮＯ＋ＣＯ反应的催化性能．结合化学分析、ＸＲＤ、ＴＰＤ和ＴＰＲ对催化剂的表征结果，探讨了该系列复合氧化物对ＮＯ分解和ＮＯ＋ＣＯ反应的催化机理.

Me_2CeO_4(M=Ca,Sr,Ba)的结构与发光特性

1998年Science上报导了一种新的一维结构发光体—Sr_2CeO_4,引起人们的关注。美国已制备出满足场发射显示器(FED)用 Sr_2CeO_4蓝色荧光粉,而且确信其用于场发射显示器具有很大的潜力。本文中合成了M_2CeO_4(M=Ca,Sr, Ba),讨论了其发光与结构的相关性。Me_2CeO_4(M=Ca,Sr, Ba)均采