外延生长Re-Ba-Cu-O(Re=Y,Er,Ho,Gd,Sm)超导薄膜的结构研究

利用平面靶直流磁控溅射装置成功地制备了外延生长 ReBa_2Cu_3O_(7-x)(Re=Y,Er,Ho,Gd,Sm)超导薄膜,其中 YBa_2Cu_3O_(7-x)薄膜的临界电流密度(77.3K)达到了1.4×10~6A/cm^2.利用 X 射线衍射和小角掠入射高能电子衍射技术分析了外延薄膜的晶体结构、晶格参数及外延取向.在(100)和(110)SrTiO_3衬底上外延生长的 ReBa_2Cu_3O_(7-x) 薄膜,由于衬底取向、衬底温度和氧分压的不同,显示出有四种不同外延取向的趋势.文中还讨论了影响薄膜外延生长的因素.     

(Y,Gd)Al3(BO3)4:Tb的真空紫外光谱特性

(Y,Gd)Al3(BO3)4属于三角晶系,具有R32的空间群,掺入Ce3 ,Tb3 杂质后,其晶格结构没有变化。(Y,Gd)Al3(BO3)4:Tb随着Gd3 摩尔浓度增大,基质吸收带红移。Gd3 和Tb3 之间存在着很有效的能量传递。Gd3 摩尔浓度在一定范围内(0~0·75mol)增大时,样品在120~300nm光谱范围内的激发强度均是增强的;但是,Gd3 浓度过高造成Gd3 的发射增强,GdAl3(BO3)4:Tb在120~240nm光谱范围内激发强度很明显下降。(Y,Gd)Al3(BO3)4:Ce,Tb在真空紫外激发下,发现Tb3 的发光明显的被Ce3 猝灭。     

Preparation,characterization, and conductivity of YLnTiZrO7 (Ln = La,Nd, Sm,and Eu)

The pyrochlore oxide of composition YLnTiZrO₇ (Ln?=?La, Nd, Sm, and Eu) was prepared by sol–gel method. All the samples were characterized by powder X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy, and impedance spectroscopy. The powder XRD and Raman studies reveal that these samples were crystallized in cubic lattice with pyrochlore structure. The Rietveld analysis of the samples was carried out to obtain the unit cell parameters and reliability factors. The broad Raman bands observed for all the samples are due to cation/anion disorder in the lattice and nanosize. The XPS analysis of the samples shows the characteristic peaks belonging to Y³⁺, Ln³⁺ (Ln?=?La, Nd, Sm, and Eu), Ti⁴⁺, and Zr⁴⁺. Electrical conductivity of YLaTiZrO₇ (YLTZ) and YEuTiZrO₇ (YETZ) samples was calculated from the impedance as a function of frequency and temperature. These samples have shown conductivity of the order of 10^?5 scm^?1 at 500 °C.     

Electronic structure and magnetic properties of the quaternary perovskites LnMn3V4O12 (Ln = La,Nd and Gd)

ABSTRACT

Structural, electronic and magnetic properties of the quaternary perovskites LnMn₃V₄O₁₂ (Ln?=?La, Nd and Gd) are calculated using generalised gradient approximation along with Hubbard potential (GGA?+?U) within the frame work of density functional theory (DFT). It is observed that the calculated lattice constants are decreases as going from La→Gd due to the lanthanide’s contraction and found consistent with the experiments. The electron charge densities show that the Ln—O bond is ionic whereas the bond between Mn/V—O is covalent. The metallic nature of these compounds is confirmed by the overall band structures. The magnetic susceptibility curves show that all these compounds are anti-ferromagnetic and the exchange interactions play vital role in the magnetic properties of these perovskites. Furthermore, the electrical resistivities calculated by BoltzTrap code also verify the metallic nature of all these compounds. This study also confirms that in these compounds Mn 3d-states electrons are responsible for the magnetic behaviour whereas V 3d-states electrons for the electronic behaviour.     

Y(BO3,PO4):Ce,Tb,Gd的发光特性研究

用ＢＰＯ４和稀土氧化为原料,通过单片灼烧,首次合成了铈、铽、钆共激活的硼磷钇绿色荧光粉,利用发射光谱和激发光谱研究了基质中Ｃｅ＾３＋、Ｔｂ＾３＋、Ｇｄ＾３＋的发光以及它们之间的相互作用结果表明在铈、铽或钆、铽的双掺杂体系中存在Ｃｅ＾３＋→Ｔｂ＾３＋、Ｇｄ＾３＋→Ｔｂ＾３＋的能量传递,而在铈、钆双掺杂的体系中却观察到了Ｃｅ＾３＋和Ｇｄ＾３＋离子之间的竞争吸收和独自发射。在铈、铽共激活的硼磷民体系中掺     

(REO)3BO3(RE=La、Gd、Y)中Pr3+的光致发光

研究了紫外光激发下,（ＲＥＯ）３ＢＯ３（ＲＥ＝Ｌa、Ｇd、Ｙ）基质中Ｐr＾３＋的光 谱性质;探讨了基质晶格、阳离子半径、Ｐr＾３＋－Ｏ＾２－键的共价性等因素对光谱性 质的影响;分析了Ｐr＾３＋的发光强度随组成变化的规律性及Ｐr＾３＋的＾３Ｐ１→＾３Ｆ２跃迁发射的自身浓度猝灭机理。     

微波热效应合成(Y,Gd)BO3:Eu3+荧光体

本文首次报道用微波热效应法合成(Y,Gd)BO3:EU3+荧光体粉晶材料,X射线粉末衍射确认为六方晶系,晶胞参数a=0.3796nm,c=0.8835nm;在589nm和613.0nm监测下,其激发光谱峰是239.0nm和240.0nm,半高宽40nm.在240.0nm激发下,589nm和612-626nm的荧光强度比为1.9/1.     

Synthesis and characterization of layered perovskite-type oxides LnSr2MnFeO7 (Ln = La, Nd, Gd, and Dy)

Layered perovskite-type oxides LnSr₂MnFeO₇, with Ln?=?La, Nd, Gd, and Dy, have been synthesized by conventional solid-state reaction method. Rietveld refinement shows that all the phases were found to crystallize with tetragonal unit cell in the space group I4/mmm. The unit cell parameters a and c decrease monotonically with decreasing effective ionic radius of the lanthanide ion. The phases show insulating behavior with no anomalous features in the entire temperature range of 150–350 K and the electrical conduction occurs by Mott’s variable range hopping mechanism. The magnetic studies suggest that the phases are antiferromagnetic and the Weiss constant (θ) increases with decreasing ionic radius of lanthanide ion.     

Nonlinear refractive index of RECOB (RE = Gd and La) crystals

The Z-scan technique is employed to obtain the nonlinear refractive index (n ₂) of the Ca₄REO(BO₃)₃ (RECOB, where RE = Gd and La) single crystals using 30 fs laser pulses centered at 780 nm for the two orthogonal orientations determined by the optical axes (X and Z) relative to the direction of propagation of the laser beam (k//Y// crystallographic b-axis). The large values of n ₂ indicate that both GdCOB and LaCOB are potential hosts for Yb:RECOB lasers operating in the Kerr-lens mode locking (KLM) regime.     

Thermoelectric properties of Gd,Y co-doped Ca3Co4O9+δ

The Ca_3−x−yGd_xY_yCo₄O_9+δ precursor powders were synthesized by the polyacrylamide gel method. The powders were sintered by the spark plasma sintering (SPS). The DTA analysis showed that the synthesis temperature of Ca₃Co₄O_9+δ was about 933 K, which is lower than that of the conventional citric acid method. The resistivities, the Seebeck coefficients and the thermal conductivities of the samples were measured from room temperature to 973 K. The Seebeck coefficients and the resistivities of the doped samples were remarkably enhanced due to the decrease of the carrier concentration, whereas the thermal conductivities of them were decreased due to the impurity scattering effect. The maximal ZT value of 0.26 was obtained at 973 K for Ca_2.7 Gd_0.15 Y_0.15Co₄O_9+δ.     

Ln7O6(BO3)(PO4)2:Eu(Ln=La,Gd,Y)的VUV-UV激发和辐射发光

本文报道了Ln 7O6(BO3)(PO4)2:Eu(Ln=La,Gd,Y)在VUV-UV区的激发光谱及Eu3+在可见区的发射光谱.其激发光谱包括基质在真空紫外区的激发带和激活剂离子在紫外区的Eu3+-O2-电荷迁移带,随La3+,Gd3+,Y3+离子半径逐渐减小,Eu3+-O2-电荷迁移带的重心位置逐渐向高能量方向移动,Gd7O6(BO3)(PO4)2:Eu和Y7O6(BO3)(PO4)2:Eu在真空紫外区的吸收与Eu3+-O2-电荷迁移带位于紫外区的吸收的比值要高于在La7O6(BO3)(PO4)2:Eu中的这个比值.激发能可被基质吸收,传递给激活剂离子,得到Eu3+的红光发射.在Gd7O6(BO3)(PO4)2:Eu中,5D0→7F1的发射强度较强,在Y7O6(BO3)(PO4)2:Eu中,5D0→7F2和5D0→7F3的跃迁较强.     

Dy3+,Sm3+和Ce3+离子在M3La2(BO3)4(M=Ca,Sr,Ba)中光谱性质的研究

本文报导了Dy3+,Sm3+和Ce3+离子在M3La2(BO3)4(M=Ca,Sr,Ba)基质中的激发与发射光谱;研究了Dy3+离子黄蓝发射的相强度随基质化合物的组成和结构的不同而呈现的变化规律;讨论了Sm3+离子电荷迁移激发带的能量与基质中近邻阳离子的关系并分析了Sm3+和Eu3+离子4f电子构型对电荷迁移带能量的影响。本文还给出了Dy3+,Sm3+和Ce3+离子发光的浓度淬灭值。     

掺Ce3+、Tb3+的M3Y2(BO3)4(M＝Ca,Sr)

采用固相反应的方法;经二次灼烧合成了掺Ce3+、Tb3+的Ca3Y2(BO3)4和Sr3Y2(BO3)4磷光体;分析了合成过程中铈的还原情况.用X-射线衍射分析确定了它们的结构均为正交晶系,空间群P21cn测定了Ce3+和Tb3+在两种基质中的光谱,得到Ce3+波长位移的某些规律,观察到Ce3+对Tb3+的敏化作用.     

均一球形PDP用荧光粉(Y,Gd)BO3:Eu的合成

利用共沉淀法通过控制稀土离子浓度、沉淀温度等得到稀土氧化物前驱体沉淀,再将其和H3BO3按化学计量比混合煅烧制备出了平均粒径在0．5～1．0μm的球形、粒径分布较小和无团聚的(Y,Gd)BO3：Eu荧光粉,其性能在一些方面优于商用荧光粉。利用X射线衍射、SEN、粒度分析仪和PL光谱进行表征。研究了不同的煅烧温度对荧光粉性能的影响,结果发现用本实验方法在800℃煅烧即可得到纯相的(Y,Gd)BO3：Eu。而传统固相合成纯相的(Y,Gd)BO3：Eu反应温度高达1200℃。因本方法工艺较易控制,适于在工业生产上推广。     

M3La(BO3)3(M=Ca,Sr,Ba)基质中Eu3+的光致发光

研究了M3La(BO3)3(M=Ca,Sr,Ba)基质中Eu3+的激发光谱和发射光谱.结果表明,最强激发峰均为394nm,并均有λ<300nm的较强电荷迁移带;按Ca-Sr-Ba的顺序,各发射峰峰值逐渐红移;Eu3+的最佳发射浓度分别为xEu3+=0.10、0.09、0.20;Eu3+的5D0→7F2跃迁发射的浓度猝灭机理分别为电偶极-四极、电偶极-偶极和电偶极-偶极相互作用.     

Structural Specific Features of Solid Solutions NdxGd1 – xCr3(BO3)4

Optics and Spectroscopy - Optical investigations of crystals of solid solutions NdxGd1&nbsp;–&nbsp;xCr3(BO3)4, 0.01 ≤ x ≤ 1, have been performed. Absorption spectra in the...     

(Y,Gd)BO3:Tb3+的真空紫外及紫外激发光谱特性

采用传统的高温固相反应法合成出（Y,Gd）BO3：Tb荧光体,对所制得的荧光体进行了晶体结构分析,分析结果表明结晶良好。（Y,Gd）BO3：Tb在147nm真空紫外光激发下的发射主峰在544nm（Tb^3＋的^5D4→^7F5跃迁）,是一种绿色发光材料。样品的真空紫外激发光谱及紫外激发光谱表明,（Y,Gd）BO3：Tb的基质吸收带位于150nm附近。Gd^3＋离子对真空紫外区的光吸收有增强作用,存在着Gd^3＋→Tb^3＋的能量传递。测量了荧光粉在室温下的荧光衰减特性,其余辉时间约为8ms,能够满足显示显像技术的要求。因此,（Y,Gd）-BO3：Tb是一种有前景的PDP用绿色发光材料。     

Na3La2(BO3)3:Sm3+的合成及其光谱特性

本文采用固相反应法,合成了一系列掺Sm^3 的Na3La2(BO3)2[Na3(La1-xSmx)2(BO3)3]发光,X－射线粉末衍射数据分析表明它们属于正交晶系,空间群为Amm2,测量了红外光谱,荧光光谱,观察到在599nm,645nm处有较强的荧光发射,并研究了发光强度与Sm^3 离子浓度（x)的关系,确定了Sm^3 离子在Na3La2(BO3)3基质中发光的适宜浓度。     

Synthesis and characterization of K2NiF4-type phases Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln = La, Nd, Gd, and Dy)

A systematic investigation of layered perovskite oxides with general formula Ln_0.5Sr_1.5Mn_0.5Fe_0.5O₄ (Ln?=?La, Nd, Gd, and Dy) has been undertaken mainly to understand their structural, magnetic, as well as electrical behavior. The materials were prepared by the ceramic method. X-ray data have been analyzed by using program Checkcell and the variations of various parameters are explained. It has been concluded that not only A-site cation radius, <r _A>, but also the size variance factor (σ ²) influence electrical and magnetic properties. A systematic study of electrical resistivity of all the four materials was undertaken as a function of temperature to understand the conduction mechanism. On analyzing the electrical resistivity data, it has been concluded that variable range hopping model is found to fit well. The magnetic studies suggest that the phases are antiferromagnetic and this behavior could arise from Mn⁴⁺–O–Mn⁴⁺, and Fe³⁺–O–Fe³⁺ superexchange interaction.