SiO2／Ag核壳复合粒子的制备与表征

首次引入活性SiO2微球作为核基，采用自组装液相还原技术，定向的在核基上沉积纳米银颗粒得到SiO2／Ag核壳复合粒子；并用红外、x射线衍射、场发射扫描电镜、能谱等分析表征该核壳复合粒子的形貌与结构。结果表明：利用活性SiO2作为核基，pH值为12．4，有表面活性剂参与的条件下，通过改变银前驱体浓度，可实现表面包覆致密、银壳厚度可控的核壳复合粒子化学制备技术。     

Synthesis of sub-micron silver and silver sulfide particles via solvothermal silver azide decomposition

Many transition-metal azides are thermodynamically unstable with respect to the elements and thus, may serve as energetic precursor sources in nanoscale metal particle synthesis. This report describes the use of silver azide (AgN₃) in nonaqueous, solvothermal decomposition reactions to produce crystalline sub-micron silver particles and interconnected structures. The thermal decomposition of AgN₃ directly produces silver and N₂ and no secondary chemical reducing agent is required. This solvothermal conversion was examined in toluene, tetrahydrofuran (THF), and trioctylamine below 250 °C. The coordinating solvents produced the smallest particles (150-500 nm), while the toluene reaction products were near 1 μm in size. The addition of soluble elemental sulfur to the THF reaction results in the growth of silver sulfide particles near 1 μm in size. The silver and Ag₂S products are crystalline by X-ray diffraction and show some faceting by scanning electron microscopy.     

Instantaneous emission brightness kinetics of zinc sulfide based electroluminescent thin-film emitters

Excited with triangular voltage pulses, electroluminescent thin-film emitters based on manganese-doped zinc sulfide exhibit a two-stage buildup and decay of the instantaneous emission brightness. The fast decay stage corresponds to the Mn²⁺ ion relaxation in zinc sulfide at a time constant of 1.4 ms. Preceding the fast stage, the slow decay stage has a time constant ten times greater and accounts for a markedly increased afterglow (phosphorescence) duration. The luminance level corresponding to the transition from the first to second stage is virtually independent of the applied voltage and the charge passed through the luminophor.     

Effect of hydrochloric acid solvent vapor annealing on spray coated silver electrode

Hydrochloric acid solvent vapor annealing (SVA) was incorporated to modify the spray coated silver electrode, and the effect of hydrochloric acid on the performance of silver electrode was systematically studied. The morphology changes of silver electrode were characterized by metallographic microscope and scanning tunneling microscope. The results showed that hydrochloric acid SVA could improve the conductivity of spray coated silver electrode and eliminate the boundary diffraction effect during spray coating process, resulting in a significant decrease of electrode boundary width from 4.91 to 1.14 μm. Furthermore, the component of silver electrode was analyzed by energy dispersive X-ray spectroscopy. It showed that hydrochloric acid could eliminate the boundary of silver electrode through etching the conductive polymer, which was the main component of electrode boundary. Based on the silver electrode of hydrochloric acid SVA, the application for electronic devices as electrode had also been realized for the fabrication of polymer solar cells.     

Photo and electroluminescence from terbium doped zinc sulfide films deposited by spray pyrolysis

Undoped, silver doped and silver-terbium doped zinc sulfide photoluminescent thin films have been prepared by the spray pyrolysis technique. The crystalline structure of the deposited films is hexagonal wurzite, in all cases. The films have a preferential growth with the (0 0 2) direction perpendicular to the surface of the substrate. In general, the relative chemical compositions show that the films are formed by a zinc rich ZnS material. The photoluminescent excitation measurements are in agreement with the optical transmission results indicating that the excitation mechanism is related to electron–hole pair generation across the ZnS band gap. The photoluminescent spectra show the typical bands associated with the transition from the ⁵D₄ level to the ⁷F₆, ⁷F₅, ⁷F₄ and ⁷F₃ levels of the Tb³⁺ ions. The emission spectra for the undoped and silver doped films show the well known self-activated emission, centered at 460 and 490 nm, respectively. The dependence of the emission intensity on the temperature shows an energy activation of 0.1 eV for competitive non-radiative transitions. Electroluminescent devices using silver-terbium doped zinc sulfide films as active layer show emission spectra similar to those observed in photoluminescence measurements but with a reduced intensity.     

Direct synthesis of strontium titanate phosphor particles with high luminescence by flame spray pyrolysis

SrTiO₃:Pr, Al phosphor particles with high luminescence intensities were directly prepared by flame spray pyrolysis without post-treatment. They had better crystallinity than those prepared by general spray pyrolysis with post-treatment and solid-state reaction methods. In addition, they had complete spherical shape and narrow size distribution. On the other hand, the particles prepared by general spray pyrolysis had irregular shape, and poorer brightness than those prepared by solid-state reaction method, while the particles prepared by flame spray pyrolysis had comparable photoluminescence and cathodoluminescence intensities with those of particles prepared by solid-state reaction method. The photoluminescence intensity of SrTiO₃:Pr, Al particles prepared by flame spray pyrolysis was as much as 4.7 times higher than that of particles prepared by general spray pyrolysis.     

Synthesis of zinc oxide/silica composite nanoparticles by flame spray pyrolysis

Zinc oxide (ZnO)/silica (SiO₂) composite nanoparticles were made by flame spray pyrolysis. The effects of the Zn/Si ratio on particle properties were examined and compared with those of the pure ZnO and SiO₂ particles made at the same conditions. Polyhedral aggregates of nano-sized primary particles were obtained in all experiments. The mixed-oxide primary particle size was smaller than that of pure oxides. The primary particles consisted of ZnO nano-crystals and amorphous SiO₂, as seen by high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) analysis using the fundamental parameter approach. The XRD size of ZnO was controlled from 1.2 to 11.3 nm by the initial precursor composition and it was consistent with HR-TEM. The composite particles exhibited an excellent thermal stability and little crystalline growth of ZnO (e.g., from 1.9 to 2.2 nm) was observed even after calcination at 600°C.     

Effect of preparation temperature on the characteristics of Eu-doped borate phosphor particles in the spray pyrolysis

Eu-doped gadolinium borate (GdBO₃:Eu) phosphor particles with fine size and uniform morphology were prepared by spray pyrolysis. The effects of the preparation temperatures on the characteristics of the GdBO₃:Eu phosphor particles prepared by spray pyrolysis were analyzed. The precursor particles obtained at preparation temperatures below 1400 °C had hollow and porous inner structures. On the other hand, the precursor particles obtained at preparation temperature of 1600 °C had dense structure and uniform morphologies. The precursor particles with glass phases were formed at high-preparation temperatures above 1400 °C. The precursor particles prepared at preparation temperature of 1400 °C turned into GdBO₃:Eu phosphor particles with fine size and regular morphology after post-treatment. The GdBO₃:Eu phosphor particles prepared from the precursor particles obtained at a preparation temperature of 1400 °C had the maximum photoluminescence intensity, which was similar to that of the commercial (Y,Gd)BO₃:Eu phosphor particles.     

喷雾热解法制备PDP用(Y,Gd)BO3:Eu球形荧光粉

为了得到无团聚的球形荧光粉颗粒以提高其物理和光学性能,以尿素为前驱体溶液中的添加剂,合成了等离子显示用(Y,Gd)BO3:Eu红色荧光粉.在喷雾热解过程中,通过前驱体溶液的性质来控制颗粒形貌,改善荧光粉的光学性能.获得的结果表明,前驱体溶液中加入尿素成分,能够影响颗粒形成过程、改善颗粒表面状态,从而可以促使最终产物具有良好的形貌和优异的发光强度.     

Synthesis and characterization of zinc oxide fine particles coated with titania/PDMS hybrid

Zinc oxide nanoparticles were coated with titania/polydimethylsiloxane hybrid by co-hydrolysis and co-condensation of the sols prepared from titanium tetraisopropoxide and methoxy-functionalized polydimethylsiloxane to synthesize a new class of hierarchically designed composite materials. The successful formation of the shell, which is composed of titania/polydimethylsiloxane hybrid, was evidenced by SEM, TEM, IR, EDS and zeta potential data. The hydrophobicity and the dispersibility in decamethylcyclopentasiloxane changed dramatically by the shell formation.     

Fabrication of hierarchically porous spherical particles by assembling mesoporous silica nanoparticles via spray drying

A new type of hierarchically porous materials is fabricated by assembling mesoporous nanoparticles via spray drying. Well-dispersed mesostructured silica nanoparticles (MSN), whose particle size distribution was narrow in the range of 20 nm and 50 nm, were prepared by a thermal deposition method. By spray drying a MSN suspension, MSN were assembled into spherical secondary particles. After calcination, the spherical particles have two types of mesopores, mesopores of 3 nm in size inside of calcined MSN and larger inter-nanoparticle mesopores of about 15-20 nm. This hierarchical pore system should provide nanospaces for efficient mass transport of guest species with different sizes.     

Preparation of silver coated nickel particles by thermal plasma with pre-treatment using ball milling

Recently, reducing noble metals in electric devices has been identified as a key factor to lower product cost. Among these, noble metal coated particles are considered an alternative with the potential to dramatically reduce the usage of noble metals. A dense coating of noble metals over all surfaces is desirable for maintaining the properties of noble metal. However, our previous research showed that coated surfaces onto which the nanoparticles were attached were non-uniform because of evaporation of the raw materials. Therefore, in this study, we improved the coverage ratio of silver coated nickel particles using thermal plasma processing followed by ball mill pre-treatment. Silver and nickel particles were mixed using a ball mill, then injected into the thermal plasma jet. The silver particles were subsequently attached onto the surface of the nickel particles through ball mill processing, after which the silver attached nickel particles were melted through thermal plasma processing to produce silver coated nickel spherical particles. The cross section of the as-prepared particles showed a dense silver shell and nickel core, while the sintered body of the as-prepared particles showed the net-like silver covering over the nickel cores. These findings suggest that attachment of silver on nickel could lead to complete silver coatings by limiting the formation of nanoparticles.     

TiO2包覆ZnS荧光粉的制备及表征

采用溶胶-凝胶法成功在ZnS荧光粉表面包覆TiO2薄膜。通过透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)、紫外可见吸收(UV-Vis)及荧光光谱(PL)对包覆前后荧光粉的结构和光学性能进行表征。结果表明:ZnS荧光粉表面包覆了一层厚度约5nm的TiO2薄膜,该薄膜整体连续性较好,分布较为均匀,且包覆过程对荧光粉的晶型及结晶度无影响,而包覆膜对ZnS的吸光度略有屏蔽且发光强度也有所降低。     

Preparation and properties of composite particles made by nano zinc oxide coated with titanium dioxide

In this paper, composite particles of nano zinc oxide coated with titanium dioxide were prepared and characterized by TEM, XRD, XPS and FT-IR, and the properties of the composite particles for photo catalysis and light absorption were studied. Tetrabutyl titanate (TBT) was hydrolyzed in an alcoholic suspension of nano zinc oxide with diethanolamine (DEA) as an additive, resulting in a film with a thickness of 20–30 nm being coated on the surface of nano zinc oxide, and the composite particles contained ZnTiO₃ after drying and calcination. Photocatalysis capabilities of the composite particles for the degradation of phenol in an aqueous solution were greatly improved as compared with nano zinc oxide particles before coating, with pure nano ZnO and nano TiO₂ with similar average sizes, or with the mixture of nano ZnO and TiO₂ with the similar composition as the composite particles. The light absorption scope of the composite particles was enlarged when compared to nano titanium dioxide with same average size.     

Y3Al5O12:Tb phosphor particles prepared by spray pyrolysis from spray solution with polymeric precursors and ammonium fluoride flux

High brightness Y₃Al₅O₁₂:Tb phosphor particles with spherical shape and fine size were prepared by spray pyrolysis from spray solution with polymeric precursors and ammonium fluoride flux. The effect of ammonium fluoride flux on the characteristics of the Y₃Al₅O₁₂:Tb phosphor particles prepared by spray pyrolysis was investigated. Ammonium fluoride flux dissolved into spray solution improved the photoluminescence intensity of the Y₃Al₅O₁₂:Tb phosphor particles prepared by spray pyrolysis. The optimum addition amount of ammonium fluoride flux to produce the maximum photoluminescence intensity was 1 wt.% of the Y₃Al₅O₁₂:Tb phosphor particles. The spherical shape of the as-prepared particles obtained by spray pyrolysis from spray solution with polymeric precursors and small amount of ammonium fluoride flux had maintained after post-treatment below 1300 °C. The optimum photoluminescence intensity of the Y₃Al₅O₁₂:Tb phosphor particles prepared from polymeric precursors and ammonium fluoride flux was 156% of that of the phosphor particles prepared from pure aqueous solution.     

Synthesis of zinc oxide particles coated multiwalled carbon nanotubes: Dielectric properties,electromagnetic interference shielding and microwave absorption

Zinc oxide (ZnO) nanoparticles were coated on the surfaces of multiwalled carbon nanotubes (MWCNTs). High resolution transmission electron microscopy images show that the wurtzite ZnO immobilized on the MWCNTs is single-crystalline with a preferential [0 0 0 2] growth direction. A capacitor was generated by the interface of ZnO and MWCNTs, and a resistor–capacitor model could well describe the relationships between the structure and the dielectric properties, electromagnetic interference shielding and microwave-absorption of the composites in the frequency range of 2–18 GHz. The network built by ZnO-immobilized MWCNTs could contribute to the improvement of electrical properties. Resonant peaks associated with the capacitor formed by the interface were observed in the microwave absorption spectra, which suggest that reflection–loss peaks greatly broadens the absorption bandwidth.