Spectroscopic Studies on Charge Transfer from Ce^3＋ to Yb^3＋ in KMgF3 ： Ce, Yb Nanocrystals

Nanocrystals of KMgF3 single-doped and codoped with Ce^3＋ or/and Yb^3＋ were synthesized separately by the mi-croemulsion method. The X-ray diffraction（XRD） patterns were indexed to show that the KMgF3 crystal system was unchanged. The fluorescent spectra of KMgF3： Ce, Yb polycrystal powders were studied and compared with those of the Ce,Yb doped KMgF3 crystals produced using the high-temperature solid phase method. The diffuse reflection spectra and infrared emission of KMgF3： Ce, Yb were investigated. From the results, the authors could confirm that there were charge transfer processes from Ce^3＋ to Yb^3＋ in both KMgF3： Ce,Yb nanocrystals and polycrystal powders.     

无氨湿法制备纳米晶In2O3及表征

Preparation of In₂O₃nano-scale powders by ultrasonic and homogeneous precipitation, using metal In and urea as raw materials, was reported for the first time, while the effects of reaction temperature, the ratio of the materials and the pH etc. on the preparation was dicussed. This method can be operated and industrialized easily with very low cost． The structural properties of precursor and In₂O₃were characterized by TG-DTA, XRD, ESCA and TEM. The results show that In₂O₃produced are very pure, monophase and spherical nano-scale powders with average size of 25 nm.     

Effects of Carrier on CuO／TiO2 and CuO／Ti0.5Zr0.5O2 Catalysts in the NO＋CO Reaction

Using TiO2 and Ti0.5Zr0.5O2 as carriers, the CuO/TiO2 and CuO/Ti0.5Zr0.5O2 catalysts were prepared by the impregnation method with Cu(NO3)2 as active component. The catalytic activities in NO CO reaction were investigated using a microreactor-GC system, and structure and reducibility of catalysts were characterized by means of physical adsorption, TPR, XRD, NO-TPD technologies. It was found that the activity of CuO/Ti0.5Zr0.5O2 catalyst was higher than that of CuO/TiO2, probably due to the large specific surface area of Ti0.5Zr0.5O2 that played an important role in NO CO reaction.     

Preparation of Pt／C Catalyst with Solid Phase Reaction Method

The Pt/C catalyst was prepared with solid phase reaction method (Pt/C(S)) for the first time.Its Performances were compared with that prepared by the traditional liquid phase reaction method. The results demonstrate that the electrocatalytic activity of Pt/C catalyst with solid phase reaction method for methanol oxidation is higher than that with liquid phase reaction method. XRD and TEM measurements indicate that the Pt/C(S) possesses low crystalline extent and small particle size.     

Gas Phase Selective Catalytic Oxidation of Toluene to Benzaldehyde on V2O5-Ag2O／η-Al2O3 Catalyst

Gas phase selective catalytic oxidation of toluene to benzaldehyde was studied on V2O5-Ag2O/η-Al2O3 catalyst prepared by impregnation. The catalyst was characterized by XRD, XPS, TEM,and FT-IR. The catalytic results showed that toluene conversion and selectivity for benzaldehyde on catalyst sample No.4 (V/(V Ag)=0.68) was higher than other catalysts with different V/Ag ratios. This was attributed to the higher surface area, larger pore volume and pore diameter of the catalyst sample No.4 than the other catalysts. The XRD patterns recorded from the catalyst before and after the oxidation reaction revealed that the new phases were developed, and this suggested that silver had entered the vanadium lattice. XPS results showed that the vanadium on the surface of No.4 and No.5 sample was more than that in the bulk, thus forming a vanadium rich layer on the surface. It was noted that when the catalyst was doped by potassium promoter, the toluene conversion and selectivity for benzalde hydewere higher than those on the undoped catalyst. This was attributed to the disordered structure of V2O5 lattice of the K-doped catalyst and a better interfacial contact between the particles.     

超细掺锑SnO2制备工艺中前驱体洗涤分离的研究

Sb-doped SnO₂ ultrafine powders were prepared via oxidation-coprecipitation. Also the relation between surface characteristic (i.e. charged status and solvation) and precursor separation was studied. The results showed that the filter washing speed of precursor can be improved by reduced Precursor |ζ| values or lessen Precursor solvation. For example, adding to little organic solvents (such as ethanol )in Washing liquid morely accelerates to separation speed of precursor. This method and principle of washing and separation precursor can be used by other nona powders preparation with precipitation method, also sb doped SnO₂ ultrafine powders will be prepared easily in industry with it.     

柠檬酸溶解-热解法合成纳米晶SnO2粉体

The SnO₂ nanocrystaline powders were synthesized by citric acid dissolution-pyrolysis method. The medium products were analyzed by FTIR. The products were characterized by TG-DTA, XRD, TEM, SEM etc. The results showed that the Sn was coordinated with aconitase acid during the dissolution. The SnO₂ particles prepared by this method were with a mean size of 5～10 nm. The calcined products presented lacunose micro-arc structure, thus favoring the application as gas-sensitive materials.     

Effect of Preparation Methods of Bi2O3 Nanoparticles on their Photocatalytic Activity

Bi2O3 nanoparticles were prepared by means of ammonia precipitation, polyol mediated methods and microemulsion chemical method. The structure and properties of the as-prepared nanoparticles, having been submitted to a heat-treatment test at 750℃, were characterized by means of XRD. BET, XPS and UV-Vis absorption techniques. The photocatalytic oxidation reactions of benzene, toluene and xylene were used as the model reaction to measure the photocatalytic activity of Bi2O3 nanoparticles, respectively. The results show that the crystallite size of Bi2O3 prepared with different methods and calcined at 750℃ were 50. 6, 38.5 and 31.5 nm, respectively. The photocatalytic activity of Bi2O3 nanoparticles prepared with the microemulsion chemical method was higher than that of the particles prepared with the polyol mediated method; and that of the particles prepared with the micromulsion chemical method was the highest among the three. The degradation rates of the three pollutants xylene, toluene and benzene decreased in sequence.     

SnO2纳米粒子的制备与表征

The SnO2 nano-particles with rutile structure were prepared by a Water/Oil (W/O) microemulsion system, composed of Triton X-100 1-hexanol/Cyclohexane/Water. The particles were also compared with that synthesized by citric acid method. The powders were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopy (IR). The result showed that the SnO2 particles prepared by microemulsion had fine shape and narrow range of particle size distribution. The crystallite size calcined at 600℃ was 11.49 nm,while the crystallite size prepared by citric acid method was about 17.4 nm.     

Effect of ultrasonic irradiation and /or halogenation on the catalytic performance of γ-Al2O3 for methanol dehydration to dimethyl ether

Dimethyl ether(DME) is amongst one of the most promising alternative,renewable and clean fuels being considered as a future energy carrier.In this study,the comparative catalytic performance of the halogenated γ-Al 2 O 3 prepared from two halogen precursors(ammonium chloride and ammonium fluoride) is presented.The impact of ultrasonic irradiation was evaluated in order to optimize both the halogen precursor for the production of DME from methanol in a fixed bed reactor.The catalysts were characterized by SEM,XRD,BET and NH 3-TPD.Under reaction conditions where the temperature ranged from 200 to 400 ℃ with a WHSV = 15.9 h-1was found that the halogenated catalysts showed higher activity at all reaction temperatures.However,the halogenated alumina catalysts prepared under the effect of ultrasonic irradiation showed higher performance of γ-Al 2 O 3 for DME formation.The chlorinated γ-Al 2 O 3 catalysts showed a higher activity and selectivity for DME production than fluorinated versions.     

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.     

Enhancement of the photoluminescence and long afterglow properties of Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript> phosphor by Dy<Superscript>3+</Superscript> co-doping

The Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺, Dy³⁺ long afterglow phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by powder X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) techniques. The luminescence properties were investigated using thermoluminescence (TL), photoluminescence (PL), long afterglow, mechanoluminescence (ML), and ML spectra techniques. The crystal structure of sintered phosphors was an akermanite type structure, which belongs to the tetragonal crystallography. TL properties of these phosphors were investigated, and the results were also compared. Under the ultraviolet excitation, the emission spectra of both prepared phosphors were composed of a broad band peaking at 535 nm, belonging to the broad emission band. When the Ca₂MgSi₂O₇:Eu²⁺ phosphor is co-doped with Dy³⁺, the PL, afterglow and ML intensity is strongly enhanced. The decay graph indicates that both the sintered phosphors contain fast decay and slow decay process. The ML intensities of Ca₂MgSi₂O₇:Eu²⁺ and Ca₂MgSi₂O₇:Eu²⁺, Dy³⁺ phosphors were proportionally increased with the increase of impact velocity, which suggests that this phosphor can be used as sensors to detect the stress of an object.     

Luminescent properties of Sr<Subscript>3</Subscript>Al<Subscript>2</Subscript>O<Subscript>6</Subscript>: Eu,Pr prepared by sol–gel method

A new red-emitting long afterglow Sr₃Al₂O₆: Eu²⁺, Pr³⁺ phosphor was synthesized by sol–gel methods using Sr(NO₃)₂, Al(NO₃)₃·9H₂O, Eu(NO₃)₃ and Pr(NO₃)₃ as raw materials. The crystalline structure of the phosphor powders were characterized by X-ray diffraction. Luminescent properties of the phosphor powders were analyzed by the fluorescence spectrophotometer. Sr₃Al₂O₆: Eu²⁺, Pr³⁺ phosphor powders with single Sr₃Al₂O₆ phase were prepared at 1200 °C for 2 h in the reducing atmosphere. Pr³⁺ doped made the light intensity and the light-lasting time of Sr₃Al₂O₆: Eu²⁺, Pr³⁺ phosphors improved. The emission peaks of the Sr₃Al₂O₆: Eu²⁺, Pr³⁺ phosphor powders lay at 612 nm with the excitation of 472 nm and the longest afterglow time could last for about 15 min at Pr³⁺ content of 0.06.     

Photocurable silica hybrid organic–inorganic films for photonic applications

This paper reports the detailed preparation process of Eu²⁺ activated Sr₃Al₂O₆ by a sol-gel method in the reducing atmosphere. The effect of the calcining temperature on the microstructure, crystalline particle morphology and luminescence properties of Sr₃Al₂O₆:Eu²⁺ is systematically discussed. X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM) and fluorescence spectrophotometer were employed to characterize the phosphor. The Sr₃Al₂O₆:Eu²⁺ phosphor powders calcined at 1200 °C for 2 h possessed a Sr₃Al₂O₆ single cubic phase. The Sr₃Al₂O₆:Eu²⁺ crystallites showed flower-like morphology. The Sr₃Al₂O₆:Eu²⁺ phosphor powders exhibited a red broad emission band with emission peak at 612 nm under 472 nm excitation. Especially the Sr₃Al₂O₆:Eu²⁺ phosphor powders prepared at 1200 °C showed the strongest luminescence intensity, due to the pure phase and higher crystallinity of Sr₃Al₂O₆.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Round‐the‐Clock Photocatalytic Hydrogen Production with High Efficiency by a Long‐Afterglow Material

Long afterglow materials can store and release light energy after illumination. A brick‐like, micrometer‐sized Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ long‐afterglow material is used for hydrogen production by the photocatalytic reforming of methanol under round‐the‐clock conditions for the first time, achieving a solar‐to‐hydrogen (STH) conversion efficiency of 5.18 %. This material is one of the most efficient photocatalysts and provides the possibility of practical use on a large scale. Its remarkable photocatalytic activity is attributed to its unique carrier migration path and large number of lattice defects. These findings expand the application scope of long afterglow materials and provide a new strategy to design efficient photocatalysts by constructing trap levels that can prolong carrier lifetimes.     

Improved water resistance of SrAl2O4: Eu2+, Dy3+ phosphor directly achieved in a water-containing medium

In this paper, a heterogeneous precipitation method utilizing urea hydrolysis was adopted to coat a SiO₂ layer on the surface of SrAl₂O₄:Eu²⁺, Dy³⁺ long persistence phosphors. To avoid phosphor hydrolysis in a water-containing coating medium, the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) were concerned and carried out. The crystal phases, surface morphologies, hydrolysis stability and water resistance on afterglow properties of coated phosphors were investigated. Scanning electron microscopy, energy dispersive spectrum analysis, transmission electron microscope and Fourier transform infrared spectrum results confirmed that a continuous, uniform and compact SiO₂ coating layer was successfully obtained on the phosphors surface. A theoretical coating amount of 5% or higher was found to be good for hydrolysis stability. Photoluminescence results revealed the coated phosphors showed much better water resistance on afterglow properties than the uncoated phosphor. We also discussed and proposed the hydrolysis restriction mechanism of SrAl₂O₄:Eu²⁺, Dy³⁺ in the water-containing coating medium.     

Photocatalysis enhancement of CaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, Nd<Superscript>3+</Superscript>@TiO<Subscript>2</Subscript> composite powders

CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were synthesized by a sol–gel method under mild conditions (i.e. low temperature and ambient pressure). The as-prepared powders were characterized by transmission electron microscopy (TEM) and analyzed by X-ray diffraction (XRD). The photocatalytic behavior of the TiO₂-base surfaces was evaluated by the degradation of nitrogen monoxide gas. It suggested that CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were composed of anatase titania and that CaAl₂O₄:Eu²⁺, Nd³⁺. TiO₂ particles were deposited on the surface of CaAl₂O₄:Eu²⁺, Nd³⁺ to form uniform film. CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders exhibited higher photocatalytic activity compared with pure TiO₂ under visible light. And the result also clearly indicated that the long afterglow phosphor absorbed and stored lights for the TiO₂ to remain photocatalytic activity in the dark.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Optical energy storage properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript>,R<Superscript>3+</Superscript> persistent luminescence materials

The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr₂MgSi₂O₇:Eu²⁺,R³⁺ material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 °C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R³⁺ co-dopants.