A new phosphor with flower-like structure and luminescent properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> long afterglow materials by sol–gel method

The flower-like phosphors of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ with high brightness and long afterglow were obtained by sol–gel method. X-ray diffraction pattern (XRD) shows that single-phased Sr₂MgSi₂O₇ phosphor is prepared by sol–gel method under 1250 °C. Scanning electron microscope (SEM) indicates that the phosphor consists of nano-sized whiskers which are detected for the first time in Eu²⁺ and Dy³⁺ co-doped long-lasting phosphorescence silicates. Furthermore, the investigation on the mechanism indicates that the internal structure and gas, liquid and solid phase effect play important roles in the formation of flower-like Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ nanostructure. Finally, the optical properties of flower-like Sr₂MgSi₂O₇ nanostructure have been characterized by photoluminescence (PL) spectra.     

Direct analysis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders by total reflection X-ray fluorescence spectrometry

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al₂O₃ ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1–10 mg mL^–1 of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 g g^–1 as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 L of the 10 mg mL^–1 slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 m, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3–7 g g^–1 range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.Dedicated to the memory of Wilhelm Fresenius     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.     

Formation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> bilayer using atomic layer deposition and its application to dynamic random access memory

To enhance film conformality together with electrical property suitable for dynamic random access memory (DRAM) capacitor dielectric, the effects of oxidant and post heat treatment were investigated on aluminum and titanium oxide (Al₂O₃–TiO₂) bilayer (ATO) thin film formed by atomic layer deposition method. For the conformal deposition of Al₂O₃ thin film, the O₃ oxidant required a higher deposition temperature, more than 450 °C, while H₂O or combined oxygen sources (H₂O+O₃) needed a wide range of deposition temperatures ranging from 250 to 450 °C. Conformal deposition of the TiO₂ thin film was achieved at around 325 °C regardless of the oxidants. The charge storage capacitance, measured from the ATO bilayer (4 nm Al₂O₃ and 2 nm TiO₂) deposited at 450 °C for Al₂O₃ and 325 °C for TiO₂ with O₃ oxidant on the phosphine-doped poly silicon trench, showed about 15% higher value than that of 5 nm Al₂O₃ single layer thin film without any increase of leakage current. To maintain the improved electrical property of the ATO bilayer for DRAM application, such as enhanced charge capacitance without increase of leakage current, upper electrode materials and post heat treatments after electrode formation must be selected carefully. Dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday.     

Laser assisted selective chemical metalization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films

Thick aluminum oxide films are prepared on Al plates by anodizing. On the ceramic surface thus obtained a very thin Ag film is deposited via vacuum thermal evaporation. The Ag/Al₂O₃/Al samples prepared are irradiated by Nd:YAG laser through a suitable metal mask in order to remove the top metal film in the exposed areas. Thus, a negative silver image of the copied mask is obtained. Further, the samples are processed in Ni electroless chemical bath activated by the rest of silver. All processing steps are studied by scanning electron microscopy (SEM). EDS X-ray mapping is applied to study the final distribution of Al and Ni in the processed areas. In addition, the DC conductivity of the fabricated Ni wires obtained is measured. The proposed new method for selective chemical deposition of electroconductive Ni onto laser microstructured Ag/Al₂O₃/Al samples is simple, versatile and not restricted to the metal/ceramic system studied as well as to the electroless deposited metal.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Eu<Superscript>3+</Superscript>-fluorescence properties in nano-crystallized SnO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glass-ceramics

Fluorescence and spectral hole burning properties of Eu³⁺ ions were studied in nanocrystals-precipitated SnO₂-SiO₂ glasses. The glasses were prepared to contain various amount of Eu₂O₃ using the sol-gel method, in which SnO₂ nanocrystals were precipitated by heating in air. In the glasses containing Eu₂O₃ less than 1%, the Eu³⁺ ions were preferentially doped in the SnO₂ nanocrystals and their fluorescence intensities were enhanced by the energy transfer due to the recombination of electrons and holes excited in SnO₂ crystals. The SnO₂ nanocrystals-precipitated glasses exhibited the persistent spectral holes with the depth of ∼25% of the total fluorescence intensities of the Eu³⁺ ions. With the increasing Eu₂O₃ concentration, the amount of SnO₂ nanocrystals decreased and the Sn⁴⁺ ions formed the random glass structure together with the silica network. This structure change induced the fluorescence intensities and the hole depth to decrease.     

Review of Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Reductant System in the Selective Catalytic Reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Ag/Al₂O₃ is a promising catalyst for the selective catalytic reduction (SCR) by hydrocarbons (HC) of NO _x in both laboratory and diesel engine bench tests. New developments of the HC-SCR of NO _x over a Ag/Al₂O₃ catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/Al₂O₃-reductant systems for the SCR of NO _x ; the low-temperature activity improvement of H₂-assisted HC-SCR of NO _x over Ag/Al₂O₃; and the application of a Ag/Al₂O₃-ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/Al₂O₃-reductant systems and H₂-assisted HC-SCR of NO _x over Ag/Al₂O₃. A SO₂-resistant surface structure in situ synthesized on Ag/Al₂O₃ by using ethanol as a reductant is proposed based on the study of the sulfate formation. These results provide new insight into the design of a high-efficiency NO _x reduction system. The diesel engine bench test results showed that a Ag/Al₂O₃-ethanol system is promising for catalytic cleaning of NO _x in diesel exhaust.     

Sol-coated preparation and characterization of macroporous α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> membrane support

A simple approach namely sol-coated technique has been developed for the low cost fabrication of macroporous ceramic under a far below common sintering temperature of alumina with large dimension grains. The prepared green support shows higher sinteractive than the one treated by wet impregnation method under the same sintering conditions. The support possesses great potential applications with 6.63–7.71 μm in pore size, 39% open porosity as well as >45 MPa mechanical strength at the sintering temperature range of 1350°– 1500°C. The results indicate that the nitrogen gas flux and pure water permeation value was 51 252.35 m³ m⁻² h⁻¹ bar⁻¹, 98.43 m³ m⁻² h⁻¹ bar⁻¹, respectively, which were more dependent on the pore structure and pore size distribution than open porosity.     

Oxidative conversion of methane and methanol on M/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite structured metal oxide catalysts (m = Ni,Cu, Zn)

A study was carried out on the properties of Ni/Al₂O₃ and Cu-ZnO/Al₂O₃ composites supported on ceramic honeycomb monoliths made from synthetic cordierite in the carbon dioxide conversion of methane and the partial oxidation of methanol. The structured nickel-alumina catalysts are significantly more efficient than the conventional granulated catalysts. The improved working stability of these catalysts was achieved by adjusting the acid-base properties of the surface by introducing sodium and potassium oxides, which leads to inhibition of surface carbonization. The hydrogen yield was close to 90% in the partial oxidation of methanol with a stoichiometric reagent ratio in the presence of the Cu-ZnO/Al₂O₃/cordierite catalyst. A synergistic effect was found, reducing the selectivity of CO formation in the presence of the Cu-ZnO catalyst relative to samples derived from the individual components Cu and ZnO. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 299–306, September–October, 2007.     

Electrochemical properties of <Emphasis Type="Italic">n</Emphasis>-sulfonatothiacalyx[4]arene complexes with Fe<Superscript>3+</Superscript> and [Co(dipy)<Subscript>3</Subscript>]<Superscript>3+</Superscript> ions

The electrochemical properties of n-sulfonatothiacalyx[4]arene (H₄XNa₄) complexes with [Co(dipy)₃]³⁺ and Fe³⁺ ions were studied by means of cyclic voltammetry in aqueous solution at pH 2.5. The observed single-electron reduction of [Co(dipy)₃]³⁺ bound extraspherically to the upper rim and Fe³⁺ ion bound intraspherically to the lower rim of n-sulfonatothiacalyx[4]arene in binary [Co(dipy)₃]³⁺ · H₃X^5?, H₃X^5? · Fe³⁺, and ternary [Co(dipy)₃]³⁺ · H₃X^5? · Fe³⁺ heterometal complexes was more difficult than in the free state. The reversible single-electron transfer to the metal ion results in lower binding energy ([Co(dipy)₃]³⁺, ΔΔG ₀ = 3.9 kJ/mol) or in full fast dissociation of the complex (Fe³⁺). The ternary complex in the solution forms the aggregates, in which inner encapsulated Fe(III) and Co(III) ions are not reduced on the electrode. Their quantitative reduction takes place by the relay mechanism of intra- and intermolecular electron transfer through electrochemically generated [Co(dipy)₃]²⁺ outer ions.     

Crystal-chemical analysis of the structures of minerals with [Hg<Subscript>2</Subscript>]<Superscript>2+</Superscript> dumbbells

An analysis of the structures of minerals with [Hg₂]²⁺ dumbbells including poyarkovite [Hg₂]₃Cl₂O₂, shakhovite [Hg₂]₂Sb(OH)₃O₃, vasilyevite Hg₂₀O₆I₃Br₂Cl(CO₃), and kelyanite [Hg₂]₆[SbO₆]BrCl₂ was carried out. The determining factor in structure formation is the ordering of the centers of the cluster groups of mercury and large anions by systems of equidistant parallel planes with d _hkl ～ 2.5–4.5 Å. The different combinations of atoms and fragments in the structure are ordered by their own pseudotranslation lattices; this probably reflects the stages of crystallization. The crystal structures under study are examples of balance between the local interatomic interactions and the forces that create long-range order for different stoichiometries, masses, and sizes of components.     

Phase relations in the CoO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system in subsolidus area

Thermal properties of Co₂FeV₃O₁₁ have been reinvestigated. It has been proved that this compound does not exhibit polymorphism. It melts incongruently at the temperature of 770±5°C and the phase with lyonsite type structure is the solid product of this melting. Phase relations in the whole subsolidus area of the CoO–V₂O₅–Fe₂O₃ system have been determined. The solidus area projection onto the component concentration triangle plane of this system has been constructed using the DTA and XRD methods. 15 subsidiary subsystems can be distinguished in this system.     

X-ray photoelectron study of the interaction of H<Subscript>2</Subscript> and H<Subscript>2</Subscript>+O<Subscript>2</Subscript> mixtures on the Pt/MoO<Subscript>3</Subscript> model catalyst

The effects of H₂ and H₂ + O₂ gas mixtures of varying composition on the state of the surface of the Pt/MoO₃ model catalyst prepared by vacuum deposition of platinum on oxidized molybdenum foil were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature and a pressure of 5–150 Torr. For samples with a large Pt/Mo ratio, the XP spectrum of large platinum particles showed that the effect of hydrogen-containing mixtures on the catalyst was accompanied by the reduction of molybdenum oxide. This effect results from the activation of molecular hydrogen due to the dissociation on platinum particles and subsequent spill-over of hydrogen atoms on the support. The effect was not observed at low platinum contents in the model catalyst (i.e., for small Pt particles). It is assumed for the catalyst that the loss of its hydrogen-activating ability is a consequence of the formation of platinum hydride. Possible participation of platinum hydride as intermediate in hydrogen oxidation to H₂O₂ is discussed.     

Hydrothermal synthesis and thermodynamic properties of 2CaO·3B<Subscript>2</Subscript>O<Subscript>3</Subscript>·H<Subscript>2</Subscript>O

2CaO·3B₂O₃·H₂O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B₂O₃·H₂O in HCl·54.572H₂O was determined. From a combination of this result with measured enthalpies of solution of H₃BO₃ in HCl·54.501H₂O and of CaO in (HCl+H₃BO₃) solution, together with the standard molar enthalpies of formation of CaO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol⁻¹ of 2CaO·3B₂O₃·H₂O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.     

Preparation and Characterization of GdTaO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> Sol-Gel Luminescence Thin Films

High quality GdTaO₄:Eu³⁺ luminescence films have been successfully prepared through a modified sol-gel process. The films were prepared using inorganic materials as raw materials, and the thermal decomposition and UV assisted technique were introduced to improve the quality of the film and reduce the period for forming the thick film. Results of structural studies by atomic force microscopy (AFM) and X-ray diffraction (XRD) showed that the surface was smooth and the structure was monoclinic with the average grain size of about 55 nm. The emission and excitation spectra of the film were investigated. Related to the transition ⁵ D₀ →⁷ F₁ and ⁵ D₀→⁷ F₂ of Eu³⁺ ions, the main luminescence peaks were observed at 591 and 611 nm respectively, and the luminescence peak at 345 nm was detected simultaneously related to the TaO₄³⁻ emission. Transmission spectrum and decay curve of the luminescence are also presented in this paper.     

Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Modeling the active centers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/SiO<Subscript>2</Subscript> and V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> supported catalysts. DFT theoretical analysis of optical properties

Within the framework of the density functional theory (DFT), the electronic structure of monooxodioxovanadium functional groups in tetrahedral coordination, which model the active centers (ACs) of fine supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂, has been analyzed. The optimal structures of three ACs as possible models of monomeric and polymeric oxovanadium forms on the carriers with low vanadium content were determined. The modified DFT method involving the time dependence of Kohn-Sham equation (TDDFT) was used for the adopted AC models to calculate the energies of the excited states, and optical spectra of the absorption in 25000–60000 cm^?1 region were reconstructed on their base. The spectrum in this region is due to O → V charge transfer. The features of electronic spectra with the charge transfer for V₂O₅/SiO₂ and V₂O₅/TiO₂ catalysts and the vibrational spectra of three AC models corresponding to the monomeric and dimeric oxovanadium forms of the supported catalysts V₂O₅/SiO₂ and V₂O₅/TiO₂ were defined. The detailed interpretation of normal vibration frequencies is given. The frequencies typical of the monomeric and dimeric oxovanadium forms on the carrier surface were identified.     

Electronic structure and chemical bonding in K<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript>

The calculations of the electronic structure of layered polyvanadate K₂V₃O₈ were made employing the spin-polarized tight-binding LMTO method. Calculated magnetic moment for K₄V₆O₁₆ compound phase equals 1.97 μ_B. V-O interactions were established to be dominating in the chemical bonding generation in this polyvanadate according to the estimated crystal orbital overlap population. The covalent bonds V(2)-V(2) in V(2)₂O₇ groups and electron density localization on vanadium atoms in isolated pyramids V(1)O₅ were found.     

Local structure and photoluminescent characteristics of Eu<Superscript>3+</Superscript> in ZnO–SiO<Subscript>2</Subscript> glasses

The photoluminescence properties of xZnO–(100−x)SiO₂ (x = 0, 5, 10, 20) containing 1% Eu₂O₃ prepared by a sol–gel method were systematically investigated. The results indicated that the relative proportion of f–f transitions to charge transfer (CT) absorption decreased with the increase of ZnO concentration. The intensity of ⁵D₀–⁷F_J transitions of Eu³⁺ ions was enhanced with the increase of ZnO content due to local structure changes and decreased quantities of Eu³⁺ ions clusters. The results of fluorescence line narrow (FLN) spectra indicated that Eu³⁺ ions occupied one site in SiO₂ glass and two sites in ZnO–SiO₂ glasses. The second-order crystal field parameters were calculated. B₂₀ and B₂₂ for site 1 increased with excitation energy, while ones hardly changed for site 2.