Y2SiO5:Ce3+荧光体的基质多面体替换及其对发光性能的调控研究

荧光材料基质的结构调制对于调控发光材料的发光性能,探索固体结构-性能关系具有重要的研究意义。本文以Y2SiO5基质为模型,分别利用Si/Al和Si/P取代,以[AlO4]和[PO4]四面体替换[SiO4]四面体,设计合成了一系列组成为Y1.95Si1-xAlxO5-xFx∶0.05Ce3+(x=0.05,x=0.1,x=0.2,x=0.4,x=1)和Y1.95-yCaySi1-yPyO5∶0.05Ce3+(y=0,y=0.02,y=0.04,y=0.06,y=0.08,y=0.2)的荧光材料。结合X射线衍射、荧光光谱、荧光寿命等测试手段对其进行了表征分析。结果表明,在x≤0.2,y≤0.04时得到的产物能够保持Y2SiO5的结构特征,在一定的基质组成替换范围内,设计合成的样品Y1.95Si1-xAlxO5-xFx∶0.05Ce3+、Y1.95-yCaySi1-yPyO5∶0.05Ce3+能提高发光强度,发射光谱呈现蓝移现象。荧光寿命测试表明这两个系列的化合物中Ce3+所处的基质环境变化较小,Ce3+发光也未产生较大的变化。     

The Crystal Chemistry of Lithium in the Alluaudite Structure: A Study of the (Na1−xLix)CdIn2(PO4)3 Solid Solution (x=0 to 1)

Several compounds of the (Na_1−xLi_x)CdIn₂(PO₄)₃ solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd²⁺ in the M(1) site, and of In³⁺ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na⁺ and Li⁺ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na⁺→Li⁺ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na_1−xLi_x)MnFe₂(PO₄)₃, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.     

空气中合成固溶体荧光粉Ba2(Zn, Mg)Si2O7:Ce3+,Eu2+,Eu3+及其发光特性

采用高温固相法在空气中合成了Ba_1.97-yZn_1-xMg_xSi₂O₇:0.03Eu,yCe³⁺系列荧光粉。分别采用X-射线衍射和荧光光谱对所合成荧光粉的物相和发光性质进行了表征。在紫外光330~360 nm激发下,固溶体荧光粉Ba_1.97-yZn_1-xMg_xSi₂O₇:0.03Eu的发射光谱在350~725 nm范围内呈现多谱峰发射,360和500 nm处有强的宽带发射属于Eu²⁺离子的4f⁶5d¹-4f⁷跃迁,590~725 nm红光区窄带谱源于Eu³⁺的⁵D₀-⁷F_J (J=1,2,3,4)跃迁,这表明,在空气气氛中,部分Eu³⁺在Ba_1.97-yZn_1-xMg_xSi₂O₇基质中被还原成了Eu²⁺;当x=0.1时,荧光粉Ba_1.97Zn_0.9Mg_0.1Si₂O₇:0.03Eu的绿色发光最强,表明Eu³⁺被还原成Eu²⁺离子的程度最大。当共掺入Ce³⁺离子后,形成Ba_1.97-yZn_0.9Mg_0.1Si₂O₇:0.03Eu,yCe³⁺荧光粉体系,其发光随着Ce³⁺离子浓度的增大由蓝绿区经白光区到达橙红区;发现名义组成为Ba_1.96Zn_0.9Mg_0.1Si₂O₇:0.01Ce³⁺,0.03Eu的荧光粉的色坐标为(0.323,0.311),接近理想白光,是一种有潜在应用价值的白光荧光粉。讨论了稀土离子在Ba₂Zn_0.9Mg_0.1Si₂O₇基质中的能量传递与发光机理。     

Modeling of self-organization processes in crystal-forming systems. Structural mechanism of self-assembly of zirconosilicate Na2ZrSi2O7 from suprapolyhedral clusters

Topological analysis of the crystal structure of Na₂ZrSi₂O₇ (parakeldyshite, space group P1^–) with an MT framework, where M are ZrO₆ octahedra and T are SiO₄ tetrahedra, was carried out by the method of coordination sequences (TOPOS.3.2 program package), and the self-organization of this structure was modeled. The cyclic-type suprapolyhedral cluster precursor Na₂M₂T₄ with the local symmetry 1^– was identified by bicolor decomposition of the 4646+664 net. The cluster is composed of six polyhedra with two Na atoms located in the center. The precursors control the evolution of high-level crystal-forming clusters. The cluster coordination number is six. The centers of eight cluster precursors in the superprecursor of the Na₂ZrSi₂O₇ structure are related by translation vectors.     

Hydrothermal synthesis of one-dimensional (1D) Na<Subscript>x</Subscript>TiO<Subscript>2</Subscript> nanostructures

Nanorods of sodium titanium dioxide bronze Na_xTiO₂ were synthesized by the hydrothermal treatment of the amorphous TiO₂·nH₂O gel with 10 M NaOH followed by ultrasonication in 0.1 M HCl and thermal treatment (500°C, 10 h). The thermal treatment of the nanorods does not change the morphology of the particles. According to the electron diffraction data, the Na_xTiO₂ nanorods grow along the c axis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 71–73, January, 2005.     

Structure and properties of a novel cobaltate La0.30CoO2

The layered cobaltate La_0.30CoO₂ was prepared from Na_xCoO₂ precursor by a solid-state ionic exchange and was characterized by means of X-ray and neutron diffraction, magnetic, thermal and electric transport measurements. The compound consists of hexagonal sheets of edge-sharing CoO₆ octahedra interleaved by lanthanum monolayers. Compared to Na⁺ in the parent system, the La³⁺ ions occupy only one-third of available sites, forming a 2-dimensional superstructure. The deviation from the ideal stoichiometry La_1/3CoO₂ introduces extra hole carriers into the diamagnetic LS Co³⁺ matrix making the sample Pauli paramagnetic. The temperature dependence of the electrical conductivity in La_0.30CoO₂ follows Mott's T^−1/3 law up to about 400 K, which is in contrast with the standard metallic behavior in the Na⁺ homolog possessing the same formal doping. The experiments are complemented by electronic structure calculations for La_0.30CoO₂ and related Na_xCoO₂ systems.     

Y2O3 and MgO co-doped ceria based electrolytes

Electrolytes of Ce_1-x-y Y _x Mg _y O_2-0.5x-y were prepared with citrate method and were characterized by inductively coupled plasma-atomic emission spectrometry, energy dispersive spectrometry, powder X-ray diffraction, and impedance spectroscopy. The effect of composition on the structure, conductivity, and stability of the electrolytes were investigated. When 0≤x≤ about 0.2 and 0≤y≤ about 0.05, the electrolytes were all single phase materials of ceria-based solid solution. However, when y> about 0.05, the electrolytes became two-phase materials, Y³⁺ and Mg²⁺ co-doped ceria-based solid solution and free MgO. The sample with nominal composition of Ce_0.815Y_0.065Mg_0.12O_2-d showed ionic conductivity at 973 K close to or even a little higher than that of similarly prepared Ce_0.9Gd_0.1O_1.95, but had lower cost of raw materials and a little better stability in reducing atmosphere. The existing of free MgO improved the stability of the electrolytes in reducing atmosphere, but too much free MgO reduced the conductivity.     

空气中合成固溶体荧光粉Ba_2(Zn,Mg)Si_2O_7∶Eu~(2+),Eu~(3+),Ce~(3+)及其发光特性

采用高温固相法在空气中合成了Ba1.97-yZn1-xMgxSi2O7∶0.03Eu,y Ce3+系列荧光粉。分别采用X-射线衍射和荧光光谱对所合成荧光粉的物相和发光性质进行了表征。在紫外光330~360 nm激发下,固溶体荧光粉Ba1.97-yZn1-xMgxSi2O7∶0.03Eu的发射光谱在350~725 nm范围内呈现多谱峰发射,360和500 nm处有强的宽带发射属于Eu2+离子的4f 65d1-4f 7跃迁,590~725 nm红光区窄带谱源于Eu3+的5D0-7FJ(J=1,2,3,4)跃迁,这表明,在空气气氛中,部分Eu3+在Ba1.97-yZn1-xMgxSi2O7基质中被还原成了Eu2+;当x=0.1时,荧光粉Ba1.97Zn0.9Mg0.1Si2O7∶0.03Eu的绿色发光最强,表明Eu3+被还原成Eu2+离子的程度最大。当共掺入Ce3+离子后,形成Ba1.97-yZn0.9Mg0.1Si2O7∶0.03Eu,y Ce3+荧光粉体系,其发光随着Ce3+离子浓度的增大由蓝绿区经白光区到达橙红区;发现名义组成为Ba1.96Zn0.9Mg0.1Si2O7∶0.03Eu,0.01Ce3+的荧光粉的色坐标为(0.323,0.311),接近理想白光,是一种有潜在应用价值的白光荧光粉。讨论了稀土离子在Ba2Zn0.9Mg0.1Si2O7基质中的能量传递与发光机理。     

Influence of partial substitution of zinc for copper on electronic structures of YBa2Cu3O y

Summary By use of an approximate band-structure treatment based on the EHMO approach, the energy band structures for the Zn-doped superconductor YBa₂Cu_3–x Zn _x O _y were calculated in the present paper and the influence of partial substitution of zinc for copper on the electronic structures for orthorhombic YBa₂Cu₃O_y was studied. From analysis of the band structures and the densities of states for YBa₂Cu_3–x Zn _x O _y , it was demonstrated that the 2D Cu-O planes in the Y-Ba-Cu-O superconducting system have a direct and dominant influence on superconductivity, whereas the role of the 1D Cu-O ribbons and the O(4) atoms is also of some importance.     

M5(PO4)3F (M=Ca, Sr, Ba)中Sm3+的电荷迁移态及Sm3+和Eu3+的电荷迁移能量关系

采用高温固相反应合成了M_5-2xSm_xNa_x(PO₄)₃F(M=Ca,Sr,Ba)荧光体,研究了其在真空紫外-可见光范围的发光特性。发现在Ca₅(PO₄)₃F中Sm³⁺的电荷迁移带约在191 nm,在Sr₅(PO₄)₃F中约在199 nm,而在Ba₅(PO₄)₃F中约在204 nm,随着被取代碱土离子半径的增大电荷迁移能量逐渐减小。比较了M₅(PO₄)₃F (M=Ca,Sr,Ba)中Sm³⁺和Eu³⁺电荷迁移能量的关系。     

Single-crystal synthesis, structure analysis, and physical properties of the calcium ferrite-type NaxTi2O4 with 0.558<x<1

Single crystals of calcium ferrite CaFe₂O₄-type NaTi₂O₄ having millimeter-sized needle shapes were synthesized by a reaction of Na metal and TiO₂ in a sealed iron vessel at 1473 K. Sodium-deficient Na_xTi₂O₄ single crystals with 0.558<x<1 were successfully synthesized by a topotactic oxidation reaction using NaTi₂O₄ single crystals as parent materials. The crystal structures of Na_xTi₂O₄ with x=0.970, 0.912, 0.799, 0.751, 0.717, 0.686, 0.611, and 0.558 were determined by the single-crystal X-ray diffraction method. The basic framework constructed by the Ti1O₆ and Ti2O₆ double rutile chains was maintained in these Na_xTi₂O₄ compounds. Based on the results of bond valence analysis, we speculated that the Ti1 sites are preferentially occupied by Ti³⁺ cations over the compositional range of 0.8<x<1, while both the Ti1 and Ti2 sites are randomly occupied by Ti³⁺ and Ti⁴⁺ cations at x=0.558. Magnetic susceptibility data indicated that the broad maximum around 40 K observed in as-grown NaTi₂O₄ is suppressed by an Na deficiency and vanishes in Na_0.717Ti₂O₄. The electrical resistivity increased with the Na deficiency; however, it was still semiconductive in Na_0.799Ti₂O₄.     

Synthesis and Properties of Solid Solutions in The FeVMoO7–CrVMoO7 System

X-ray phase analysis (XRD), differential thermal analysis (DTA) and IR spectroscopy have shown that continuous substitution solid solutionsin are formed in the FeVMoO₇–CrVMoO₇ system. With increasing the degree of Cr³⁺ ion incorporation into the FeVMoO₇ structure, a crystal lattice contraction of the Fe_1–xCrxVMoO₇ solid solution arise. Elevation of temperature of its incongruent melting and gradual shifting of the corresponding IR absorption bands towards higher wavenumbers have been noticed, as well. The solid product of incongruent melting for x≤0.5 is the Fe_4–yCr_yV₂ Mo₃ O₂₀ solid solutions phase, whereas for x>0.5 Fe_2–zCr_z(MoO₄)₃ and Fe_2–u Cr_u O₃ solid solutions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Properties of The Solid Solutions Formed in The Fe2V4O13–Cr2V4O13 System

DTA and XRD studies of the Fe₂V₄O₁₃–Cr₂V₄ O₁₃ system have shown that continuous solid solutions of a Fe_2–xCr_xV₄O₁₃ type, bearing a Fe₂ V₄ O₁₃ structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe₂ V₄ O₁₃ structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe_2–x Cr_x V₄ O₁₃ type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr³⁺ ion incorporation. The solid product of melting Fe_2–x Cr_x V₄ O₁₃ solid solutions for 0.2<x >1.2 is the Fe_1–x Cr_x VO₄ solution phase, and for x ≤0.2 and x ≥1.4 – the Fe_1–x Cr_x VO₄ phase as well as FeVO₄ or CrVO₄ , respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electronic structures of superconductors YBa2Cu3−x M x O y (M=Sn,Ni)

Based on the EHMO approach, the energy band structures for superconductors YBa₂Cu_3–x Sn _x O _y (y>7) and YBa₂Cu_3–x Ni _x O_y (y<7) were calulated in the present paper. The influence of the cation doping at the Cu site in the unit cell and the oxygen content on their electronic structures was studied. The results showed that the cation doping at the Cu site resulted in the great decreases in the bandwidths of the broad anisotropic Cu-O bands and the densities of states. In YBa₂Cu_3–x Sn _x O _y , however, these decreases are compensated by the increase in the oxygen content caused by the Sn-doping, which results in a small change in the total densities of states. For YBa₂Cu_3–x Ni _x O _y , the effect of the doping on its electronic structures in dominant. The Ni-doping, therefore, results in a great change in the electronic structures. In addition, the study on the projected densities of states of the Ni-doped system revealed that the 2D Cu-O planes in the Y-Ba-Cu-O system played a dominant role in superconductivity.     

正极材料Li(Ni0.5Mn0.5)1-xMxO2 (M=Ti，Al；x=0，0.02)电化学行为的比较研究

0IntroductionMany efforts have been made to develop newmaterials as an alternative to LiCoO2due to the rela-tively high cost and toxicity of Co.Much attention hasbeen paid to layered structure cathode materials suchas LiMnO2and LiNiO2due to their lower co…     

Synthesis and electrochemical properties of nanostructured LiAl x Mn2 − x O4 − y Br y particles

Nanostructured LiAl _x Mn_2 − x O_4 − y Br _y particles were synthesized successfully by annealing the mixed precursors, which were prepared by room-temperature solid-state coordination method using lithium acetate, manganese acetate, lithium bromide, aluminum nitrate, citric acid, and polyethylene glycol 400 as starting materials. X-ray diffractometer patterns indicated that the particles of the as-synthesized samples are well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiAl _x Mn_2 − x O_4 − y Br _y samples consist of small-sized nanoparticles. The results of galvanostatic cycling tests revealed that the initial discharge capacity of LiAl_0.05Mn_1.95O_3.95Br_0.05 is 119 mAh g⁻¹; after the 100th cycle, its discharge capacity still remains at 92 mAh g⁻¹. The introduction of Al and Br in LiMn₂O₄ bring a synergetic effect and is quite effective in increasing the capacity and elevating cycling performance.     

XRD and UV-Vis diffuse reflectance analysis of CeO2-ZrO2 solid solutions synthesized by combustion method

A series of ceria-incorporated zirconia (Ce_1−xZr_xO₂,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard’s law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce³⁺ ← O²⁻and Ce⁴⁺ ← O²⁻ charge transfer transitions. The two vibrational bands in 6960 cm⁻¹ and 5168 cm⁻¹ in the NIR region indicate the presence of surface hydroxyl groups on these materials.     

Preparation and Characterization of SiO2-MxOy(M = V, Sn, Sb) Thin Films from Silicic Acid and Metal Chlorides

The preparation of SiO₂-M _x O _y (M = V, Sn, Sb) binary oxide thin films by sol-gel method was investigated. The reaction of silicic acid with metal chloride (M = Sn and Sb) or oxychloride (M = V) formed homogeneous solutions. The dip-coating of slide glass and silicon wafer followed by heat treatment gave oxide films having Si—O—M bond. The changes of FT-IR spectra as a function of heat treatment temperature and molar composition confirmed the Si—O—M bonds. The sheet resistance of films increased with an increase on heat treatment temperature and decrease in the content of metal oxide M _x O _y . X-ray diffraction peaks were observed for the SiO₂-V₂O₅ films with high V₂O₅ contents and heat-treated above 250°C, while the others were amorphous. Oxide films heat treated at 500°C had a thickness between 340–470 nm.     

Ce1－xNdxO2－δ固溶体的电子顺磁共振谱和阻抗谱的研究

利用溶胶-凝胶方法在800 ℃焙烧10 h后, 合成了固溶体Ce_1－xNd_xO_2－δ (x＝0.05～0.55), X射线衍射(XRD)测试表明固溶体已经形成立方萤石结构; 电子顺磁共振谱(EPR)研究表明在固溶体Ce_1－xNd_xO_2－δ中随着掺杂量x的增大, Ce^3＋离子含量减少, 说明掺杂Nd^3＋离子可以抑制Ce^4＋的还原; 交流阻抗谱的测量表明固溶体Ce_0.9Nd_0.1O_2－d 具有离子导电特性, 600和700 ℃时的电导率分别为4.25×10^－3和1.12×10^－2 S•cm^－1, 活化能为0.68 eV.     

Thermochemistry of Li1+xMn2−xO4 (0?x?1/3) spinel

Lithium substituted Li_1+xMn_2−xO₄ spinel samples in the entire solid solution range (0?x?1/3) were synthesized by solid-state reaction. The samples with x<0.25 are stoichiometric and those with x?0.25 are oxygen deficient. High-temperature oxide melt solution calorimetry in molten 3Na₂O·4MoO₃ at 974 K was performed to determine their enthalpies of formation from constituent binary oxides at 298 K. The cubic lattice parameter was determined from least-squares fitting of powder XRD data. The variations of the enthalpy of formation from oxides and the lattice parameter with x follow similar trends. The enthalpy of formation from oxides becomes more exothermic with x for stoichiometric compounds (x<0.25) and deviates endothermically from this trend for oxygen-deficient samples (x?0.25). This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn³⁺ to Mn⁴⁺ versus formation of oxygen vacancies). For stoichiometric spinels, the oxidation of Mn³⁺ to Mn⁴⁺ is dominant, whereas for oxygen-deficient compounds both mechanisms are operative. The endothermic deviation is ascribed to the large endothermic enthalpy of reduction.