Vacuum Ultraviolet Excited Photoluminescence Properties of Y2O2S：Eu^3＋,Bi^3＋ Phosphor

As an Hg-free lamp using phosphor, the Bi^3＋ and EH^3＋ co-doped Y2O2S phosphors were prepared and their luminescence properties under vacuum ultraviolet（VUV） excitation were investigated. The VUV photoluminescent intensity of Y2O2S：Eu^3＋ was weak, however, considerably stronger red emission at 626 nm with good color purity was observed in Y2O2S：Eu^3＋,Bi^3＋ systems. Investigation on the photoluminescence reveals that the strong VUV luminescence of Y2O2S：Eu^3＋,Bi^3＋ at 147 nm is mainly because the Bi^3＋ acts as a medium and effectively performs the energy transfer process： Y^3＋-O^2-→Bi^3＋→Eu^3＋, while the intense emission band at 172 nm is attributed to the absorption of the characteristic ^1So-^1P1 transition of Bi^3＋ and the direct energy transfer from Bi^3＋ to Eu^3＋. The Y2O2S：Eu^3＋,Bi^3＋ shows excellent VUV optical properties compared with the commercial （Y,Gd）BO3：Eu^3＋. Thus, the Y2O2S：Eu^3＋,Bi^3＋ can be a potential red VUV-excited candidate applied in Hg-free lamps for backlight of liquid crystal display.     

Synthese von Y2O2(CN2) und Leuchtstoffeigenschaften von Y2O2(CN2):Eu

Synthesis of Y₂O₂(CN₂) and Luminescence Properties of Y₂O₂(CN₂):Eu Crystalline powders of the new compound Y₂O₂(CN₂) were prepared by solid state reactions from different mixtures of YCl₃/YOCl/Y₂O₃ and Li₂(CN₂) at temperatures between 620 °C and 650 °C. Structure refinements based on X‐ray powder diffraction revealed that trigonal Y₂O₂(CN₂) crystallizes with a structure that is closely related to that of Y₂O₂S, whereas linear N‐C‐N units replace sulphur atoms in Y₂O₂S. In addition, a hexagonal polytype of Y₂O₂(CN₂) was obtained in which a different stacking sequence of yttrium atoms creates a doubling of the c‐axis. Europium‐doped samples of Y₂O₂(CN₂) were prepared and the luminescence properties of Y₂O₂(CN₂):Eu are presented.     

Interaction in the Ga2S3-Y2O2S system

The phase diagram of the Ga₂S₃-Y₂O₂S system has been investigated by differential thermal, X-ray powder diffraction, microstructural, and thermodynamic analyses. It has been established that the system is eutectic, and solubility at 295 K from the Ga₂S₃ side reaches 3 mol % Y₂O₂S. The coordinates of the eutectic point are 14 mol % Y₂O₂S and 1320 K.     

Die Tieftemperatur-Synthese von Oxidhalogeniden,YOX (X = Cl,Br, I), als Quelle der Verunreinigung von Yttriumtrihalogeniden,YX3, bei der Gewinnung nach der Ammoniumhalogenid-Methode. Die Analogie von YOCl und YSCl

Low-Temperature Synthesis of Oxyhalides, YOX (X = Cl, Br, I), as the Source of Impurity in the Preparation of Trihalides, YX₃, via the Ammonium Halide Route. Analogy of YOCl and YSCl Ammonium halides, NH₄X (X = Cl, Br, I), react with Y₂O₃ and Y₂S₃, respectively, at temperatures as low as 230=C (X = Cl), 280=C (Br), and 360=C (I) (molar ratio 12:1) to yield (NH₄)₃YX₆, NH₃, and H₂O (H₂S). The choice of smaller ratios than 12:1 (for example 2:1) results in the formation of oxyhalides, YOX, via the reaction of (NH₄)₃YX₆ with surplus Y₂O₃. This reaction is therefore the actual source of impurity of rare-earth trihalides in their preparation via the ammonium halide routes.     

Quantum chemical modeling of the mechanism of formation of bis-ligand Co(II) complexes based on polydentate heterocyclic azomethine derivatives: Competition between four-, five-, and six-coordination

The molecular structures and relative energies of four-, five-, and six-coordinate stereoisomers of bis-ligand Co(II) complexes based on polydentate heterocyclic azomethine derivatives (CoN₂O₂, CoN₂O₂Y, and CoN₂O₂Y₂ coordination units of the isomers (Y = S, Se)) were calculated using density functional theory. In terms of the proposed quantum chemical model for the mechanism of CoL₂ complex formation, the fivecoordinate structure of complexes with non-equivalent ligands, one being tridentate and the other being bidentate is most probable; this result is in line with experimental data.     

Fluorite-related phases Ln3MO7, Ln = Rare-earth,Y or Sc, M = Nb,Sb or Ta. III. Structure of the non-stoichiometric Y3TaO7 phase

The orthorhombic fluorite-related superstructure phase Y₃TaO₇ is non-stoichiometric; the Y₂O₃ content may be varied from 75.0 to about 72.5 mole% without incurring structural changes. For overall Y₂O₃ contents from 72.0 to 70.5 mole%, the crystal symmetry changes from C222₁ to Cmmm, and the c axis becomes halved. The structure of the low-Y₂O₃ material has been determined from powder X-ray diffraction intensities supplemented by single crystal electron-optical data. The relationship of this structure to that of stoichiometric Y₃TaO₇ is discussed.     

Quantum-Chemical Simulation of Tetra-, Penta-, and Hexacoordinated Stereoisomers of Bis-Ligand Ni(II) Complexes based on Polydentate Heterocyclic Derivatives of Azomethines

Molecular structures and relative energies of tetra-, penta-, and hexacoordinated stereoisomers of bis-ligand Ni(II) complexes based on polydentate heterocyclic derivatives of azomethines [coordination nodes of isomers NiN₂O₂, NiN₂O₂Y, NiN₂O₂Y₂ (Y = S, Se)] were calculated using density functional theory. Within the framework of the proposed quantum chemical model of the mechanism of formation of NiL₂ complexes (taking into account the possibility of subsequent stereoisomerization) the most probable product of complex formation was found to be the isomer with pentacoordinated central metal atom and nonequivalent ligands, tridentate and bidentate.     

Synthesis of SiO2/Y2O3:Eu core-shell materials and hollow spheres

The SiO₂/Y₂O₃:Eu core-shell materials and hollow spheres were first synthesized by a template-mediated method. X-ray diffraction patterns indicated that the broadened diffraction peaks result from nanocrystals of Y₂O₃:Eu shells and hollow spheres. X-ray photoelectron spectra showed that the Y₂O₃:Eu shells are linked with silica cores by Si-O-Y chemical bond. SEM and TEM observations showed that the size of SiO₂/Y₂O₃:Eu core-shell structure is in the range of 140-180 nm, and the thickness of Y₂O₃:Eu hollow spherical shell is about 20-40 nm. The photoluminescence spectra of SiO₂/Y₂O₃:Eu core-shell materials and Y₂O₃:Eu hollow spheres have better red luminescent properties, and the broadened emission bands came from the size effects of nanocrystals composed of Y₂O₃:Eu shell.     

Synthesis, crystal structures and luminescence properties of the Eu-doped yttrium oxotellurates(IV) Y2Te4O11 and Y2Te5O13

Y₂Te₄O₁₁:Eu³⁺ and Y₂Te₅O₁₃:Eu³⁺ single crystals in sub-millimeter scale were synthesized from the binary oxides (Y₂O₃, Eu₂O₃ and TeO₂) using CsCl as fluxing agent. Crystallographic structures of the undoped yttrium oxotellurates(IV) Y₂Te₄O₁₁ and Y₂Te₅O₁₃ have been determined and refined from single-crystal X-ray diffraction data. In Y₂Te₄O₁₁, a layered structure is present where the reticulated sheets consisting of edge-sharing [YO₈]¹³⁻ polyhedra are interconnected by the oxotellurate(IV) units, whereas in Y₂Te₅O₁₃ only double chains of condensed yttrium-oxygen polyhedra with coordination numbers of 7 and 8 are left, now linked in two crystallographic directions by the oxotellurate(IV) entities. The Eu³⁺ luminescence spectra and the decay time from different energy levels of the doped compounds were investigated and all detected emission levels were identified. Luminescence properties of the Eu³⁺ cations have been interpreted in consideration of the now accessible detailed crystallographic data of the yttrium compounds, providing the possibility to examine the influence of the local symmetry of the oxygen coordination spheres.     

Standard free energy of formation of YFeO3, Y3Fe5O12, and a new compound YFe2O4 in the FeFe2O3Y2O3 system at 1200°C

The phase equilibria in the FeFe₂O₃Y₂O₃ system have been established at 1200°C. The following phases were stable: yttria, hematite, magnetite, wüstite, metallic iron, yttrium-iron perovskite, yttrium-iron garnet, and a new phase YFe₂O₄, belonging to a rhombohedral crystal system. The YFe₂O₄ compound has a solid solution from YFe₂O_3.905 to YFe₂O_4.000. The standard free energies of formation of YFe₂O_3.905, YFeO₃, and Y₃Fe₅O₁₂ have been determined to be ?96 800 ± 200 cal, ?59 800 ± 200 cal, and ?143 700 ± 600 cal, respectively, from metallic iron, Y₂O₃, and oxygen.     

Estimation of melting (decomposition) heat of some compounds in the Y−Ba−Cu−O system

A thermodynamical method for the estimation of decomposition heat in a crystal state, incongrous and congruous melting of compounds with the use of temperature dependencies of total entropies of compounds was suggested. Entropies and heats of phase transformation of YBa₂Cu₃O₆, YBa₂Cu₃O₇, YBa₂Cu_3.5O_7.5, YBa₂Cu₄O₈, YBa₂Cu₅O₉, YBa₄Cu₃O_8.5, Y₂BaO₄, Y₂Ba₂O₅, Y₂Ba₄O₇, Y₄Ba₃O₉, YCuO₂, Y₂Cu₂O₅, Y₂BaCu₂O₅, Ba₂CuO₃, BaCuO₂, BaCu₂O₂, Ba₃Cu₅O₈ were calculated. Data, obtained by the authors earlier, are discussed.     

New Y(La)-M-O Binary Systems (M = Ca,Sr, or Ba): Synthesis,Physicochemical Characterization,and Application As the Supports of Ruthenium Catalysts for Ammonia Synthesis

The effect of the nature of the alkaline-earth metal on the phase composition and specific surface area of new Y(La)-M-O binary oxide compositions (M = Ca, Sr, or Ba) prepared by coprecipitation was studied. These systems were found to contain mixed compounds (M₂Y₂O₅, MY₂O₄, and MLa₂O₄), which are different in thermal stability, in addition to individual La₂O₃ or Y₂O₃ phases. The Y(La)-M-O compositions calcined at 450°C were characterized by a more developed specific surface area, as compared with that of individual La₂O₃ or Y₂O₃. An increase in the calcination temperature to 650°C was accompanied by a decrease in the specific surface area of binary compositions. Catalysts prepared by supporting K₂[Ru₄(CO)₁₃] onto the Y(La)-M-O systems were active in ammonia synthesis at 250-400°C and atmospheric pressure. The most active of these catalysts, K₂[Ru₄(CO)₁₃]/Y-Ba-O, provided a higher yield of NH₃ at 250-300°C than analogous catalysts prepared with the use of well-known supports (Sibunit, CFC-1, and C/MgO).     

Excellent cycling stability of spherical spinel LiMn2O4 by Y2O3 coating for lithium-ion batteries

The Y₂O₃ nano-film is coated on the surface of the spherical spinel LiMn₂O₄ by precipitation method and subsequent heat treatment at 550 °C for 5 h in air. The structure and performance of the bare LiMn₂O₄ and Y₂O₃-coated LiMn₂O₄ are characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive analysis X-ray spectroscopy, galvanostatic charge–discharge, cyclic voltammetry, and impedance spectroscopy. It has been found that the addition of Y₂O₃ does not change the bulk structure of LiMn₂O₄, and the thickness of the Y₂O₃ coating layer is approximate to 3.0 nm. The 1 wt% Y₂O₃-coated LiMn₂O₄ electrode reveals excellent cycling performance with 80.3 % capacity retention after 500 cycles at 1 C at 25 °C. When cycling at elevated temperature 55 °C, the as-prepared sample still shows 76.7 % capacity retention after 500 cycles. These remarkable improvements indicate that thin Y₂O₃ coating on the surface of LiMn₂O₄ is an effective way to improve the electrochemistry performance. Besides, the suppression of Mn dissolution into the electrolyte via the Y₂O₃ coating layer can be accounted for the improved performances.     

Solution combustion synthesized Y2O3 nanoparticles and influence of Dy doping on their microstructural,optical, and photoluminescence characteristics

Dy-doped Y₂O₃ nanoparticles were synthesized by solution combustion route with urea as fuel, and their microstructural features were analyzed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The XRD study confirms the formation of a pure cubic phase of Y₂O₃, with the maximum textural coefficient along the (2 2 2) plane for the Dy-doped samples. The lattice fringes in the HRTEM image and the bright spotty rings in the selected area electron diffraction (SAED) pattern reveal the highly crystalline nature of the nanoparticles. From the diffuse reflectance spectroscopy, using Kubelka-Monk theory, the direct bandgap energy is estimated to be 5.61 eV for the undoped Y₂O₃, which is found to decrease upon Dy³⁺ doping. The room-temperature excitation spectra of the nanoparticles recorded at 575 nm emission wavelength comprise several excitation bands corresponding to the f-f transitions of Dy³⁺ ions in the host lattice. The photoluminescence spectra of the nanoparticles excited at the wavelength of 350 nm comprise three visible emission peaks at 477 nm (blue), 573 nm (yellow), and 666 nm (red). It has been concluded that the 0.5 mol% Dy-doped Y₂O₃ nanoparticles are the potential candidate to be used for solid-state luminescent device applications.     

Thermochemical investigation of Re2O3—SeO2 systems: III. Yttrium selenium oxides in the pseudo-binary system

Ternary pure phases in the thermodynamical equilibrium Y₂Se_xO_3+2x in the pseudo-binary Y₂O₃-SeO₂ system have been synthesized by solid state reactions and characterized by X-ray powder diffraction, IR spectroscopy and DSC measurements. A new phase Y₂Se_3.5O₁₀ was found besides the known phases Y₂Se₄O₁₁, Y₂Se₃O₉ and Y₂SeO₅. The thermal decomposition properties of the compounds have been determined by total pressure measurements and their thermodynamics data have been derived from their decomposition functions and C_p values. The phase diagram and the phase barogram have been established.This revised version was published online in November 2005 with corrections to the Cover Date.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> phase diagram

Phase relations in the Y₂O₃-Ga₂O₃ system were studied by the anneal-and-quench technique in air within 1000–2300°C, and a phase diagram was plotted. Three compounds were found to form: Y₃GaO₆, Y₄Ga₂O₉, and Y₃Ga₅O₁₂; the temperature and concentration bounds of stability were determined for these compounds. Indexing results for Y₃GaO₆ are given.     

Nano-crystalline zirconia: a viable adsorbent for the column chromatographic separation of 58Co from neutron irradiated nickel targets

Owing to the high chemical reactivity of molten uranium alloys, the use of traditional graphite crucibles for casting fuel slugs for a sodium-cooled fast reactor (SFR) is problematic. Moreover, rare earth (RE) elements retained in the fuel slugs for an SFR, which are extracted from the spent fuel by pyro-processing, are more reactive than uranium melt. Therefore, in this study, Y₂O₃ single-layer coatings with thicknesses of approximately 50, 70, and 120 μm and double-layer coatings of TaC/Y₂O₃ and Y₂O₃/TaC were plasma-sprayed onto niobium substrates and tested for thermal shock resistance and compatibility against U–10 wt% Zr and U–10 wt% Zr–5 wt% RE melt. The Y₂O₃ single-layer coating, regardless of coating thickness, and the TaC/Y₂O₃ double-layer coating showed good contact at the interface between the coating and the niobium substrate, with no deterioration after the thermal cycling test. In the interaction studies, the single- and double-layer coatings showed good compatibility with the U–Zr melt. However, the Y₂O₃ coatings with thicknesses of approximately 50 and 70 μm showed severe penetration of the U–Zr–RE melt and reacted with the niobium substrate. The single-layer Y₂O₃ coating with a thickness of 120 μm and the double-layer TaC/Y₂O₃ coating exhibited the most promising performance among the candidate coatings.     

Estimation of average heat capacities of condensed phase transformation products in the Y−Ba−Cu−O system

A method of calculation of average heat capacities of phase transformation products of complex oxides is suggested. The method takes into account the physical state of products and the increase in the heat capacities of products due to the change of entropy at a phase transformation. Average heat capacities of products formed in a congruous melting of compounds (YCuO₂ and Y₄Ba₃O₉), in an incongruous melting of compounds (Y₂Cu₂O₅, BaCuO₂, BaCu₂O₂, Y₂BaCuO₅, YBa₂Cu₃O₇, YBa₂Cu₃O₆) and in a decomposition in a crystalline state of compounds (Y₂BaO₄, Y₂Ba₂O₅, Y₂Ba₄O₇, Ba₂CuO₃, Ba₃Cu₅O₈, YBa₂Cu_3.5O_7.5, YBa₂Cu₄O₈, YBa₂Cu₅O₉) was estimated by using three methods.     

Degradation of carboxylic acids on Y2O3 surface under UV light. Synergism by semiconductors

Under UV light formic, oxalic, acetic and citric acids undergo degradation on the surface of Y₂O₃, an insulator. The oxidation of oxalic acid displays first-order kinetics with a linear dependence on light intensity. The photonic efficiency is lower with UV-A light than with UV-C light. While particulate TiO₂, ZnO, CuO, Bi₂O₃ and Nb₂O₅ individually photocatalyze the oxidation, each semiconductor when present along with Y₂O₃ shows synergism, indicating interparticle electron-jump from oxalic acid-adsorbed Y₂O₃ to the band gap-excited semiconductor on collision. The ease of photodegradation of the acids on Y₂O₃ is as follows: formic>oxalic>acetic>citric.     

Structure,Texture, and Acid-Base Properties of Alkaline Earth Oxides,Rare Earth Oxides,and Binary Oxide Systems

The effect of synthesis conditions on the formation of the phase composition, dispersity, pore structure, and acid-base properties of alkaline earth oxides, rare earth oxides, and the Mg-M-O (M = Y, La, or Ce) and Y(La)-M-O (M = Ca, Sr, or Ba) binary systems was studied. It was found that the nature of the system was responsible for the character of phase transformations: the Mg-M-O samples were a mixture of either MgO with Y₂O₃ or MgO with a solid solution based on rare earth oxides (LaMg)₂O₃ or (CeMg)O₂); the Y(La)-M-O samples (M = Ca, Sr, or Ba) contained the M₂Y₂O₅, MY₂O₄, and MLa₂O₄ compounds, which differ in chemical stability, in addition to La₂O₃ and Y₂O₃ phases. According to XPS data, the M/Mg atomic ratios were much higher than the bulk values; this is indicative of an enrichment of the surface of samples in the second component. An increase in the concentration of M₂O₃ from 5 to 25 mol % resulted in a decrease in the S_sp of the Mg-M-O samples from 220 ± 10 to 110 ± 10 m²/g; the S_sp of samples calcined at 750°C was lower by a factor of ～1.5–2. The S_sp of the Y(La)-M-O samples was higher than the S_sp of individual La₂O₃ and Y₂O₃. The samples were characterized by a biporous texture. The concentrations and strength distributions of surface OH groups, Lewis acid sites, and Lewis base sites depend on the nature and concentration of rare earth elements in the binary samples. The activity of the Mg-M-O samples in the oxidative dehydrogenation reaction of propionitrile correlated with the acid-base surface sites. Among the Ru/Y(La)-M-O catalysts for ammonia synthesis, Ru/Y-Ba-O was the most active; this catalyst provided a higher yield of NH₃ at 250–300°C, as compared with catalysts prepared with the use of other supports (Sibunit, KVU-1, and C/MgO).