Solid-state NMR and TGA studies of silver reduction in chabazite

Silver-exchanged molecular sieves have shown great promise in applications ranging from antimicrobial materials to the adsorption of xenon and iodide, two key contaminants emitted from nuclear reactors. In this work, solid-state 27Al and 29Si MAS NMR and TGA were used to study silver reduction in silver-exchanged chabazite under various thermal conditions. The solid-state NMR results for both 27Al and 29Si show that there are no major changes in the chabazite during silver reduction in an argon stream; however a progressive structural change does take place in the hydrogen stream. The structural change likely involves breaking the silicon oxygen bond of the Si-O-AI fragment of chabazite, leading to the formation of extra-framework aluminum oxide. The TGA results at temperatures up to 600 degrees C indicate that silver reduction is less complete in an argon stream than in a hydrogen stream. In this paper we propose that silver reduction occurs via the following reactions: 2(Ag + ZO-)+H2O --> 1/2O2+2Ag0 + 2ZOH and nAg + mAg = Ag(m+n)n+ (in an argon stream); and Ag(+) + ZO(-) + 1/2H2 = Ag0 + ZOH and 2ZOH = ZO(-) + Z(+) + H2O (in a hydrogen stream).     

Inclusion of CdSe quantum dots on the P-doped emitter of Si solar cells

We investigated Cadium Selenide quantum dots embedded in the Si solar cell in order to improve the efficiency of conventional Si solar cell. CdSe quantum dots with 3 to approximately 4 nm size were printed on the phospho-silicate glass layer grown over the emitter surface of p-n junction Si solar cells during the phosphorous diffusion process. Ohmic contact was formed by the contribution of nanoparticles at the Si emitter in spite of the existance of phospho-silicate glass layer. The enhanced light absorption due to the quantum dots was ranged from 500 to 600 nm where the CdSe nanodots have the corresponding emission wavelength of 560 nm. The efficiency of reference solar cell with the glass layer was measured to be 1.0% and it was increased to 12.72% for the reference sample without the glass layer. Furthermore, the efficiency of CdSe quantum dot sample was measured to be 13.6%. This indicates that the quantum dots play the roles of both the formation of tunneling channel and the enhancement of the light conversion efficiency in the visible spectral range.     

Silver doping of silica-hafnia waveguides containing Tb3+/Yb3+ rare earths for downconversion in PV solar cells

The aim of this paper is to study the possibility to obtain an efficient downconverting waveguide which combines the quantum cutting properties of Tb³⁺/Yb³⁺ codoped materials with the optical sensitizing effects provided by silver doping. The preparation of 70SiO₂–30HfO₂ glass and glass-ceramic waveguides by sol-gel route, followed by Ag doping by immersion in molten salt bath is reported. The films were subsequently annealed in air to induce the migration and/or aggregation of the metal ions. Results of compositional and optical characterization are given, providing evidence for the successful introduction of Ag in the films, while the photoluminescence emission is strongly dependent on the annealing conditions. These films could find potential applications as downshifting layers to increase the efficiency of PV solar cells.     

含Ag量子点钠硼硅玻璃的三阶非线性光学性质

以正硅酸乙酯、硼酸、金属钠为前驱体采用溶胶-凝胶法合成含Ag量子点的钠硼硅玻璃。X射线粉末衍射 (XRD) 分析Ag量子点具有立方相。通过透射电子显微镜 (TEM) 和高分辨透射电子显微镜 (HRTEM) 测定量子点的尺寸和分布, 结果显示在玻璃中量子点呈规则的球形, 并且尺寸在5~13 nm之间。紫外-可见(UV-Vis)吸收光谱仪得到Ag量子点的表面等离子体共振吸收峰大约在406 nm附近; 利用飞秒Z-scan 技术在800 nm波长处用飞秒钛宝石激光辐照对Ag量子点玻璃的非线性光学性质进行研究, 该玻璃的非线性折射率γ、非线性吸收系数β和三阶非线性极化率χ⁽³⁾分别为 –1.72×10^-17 m²/W、9.96×10^-11 m/W、1.01×10^-11 esu。     

补加合金成分对铝合金熔体直接氧化生长的影响

为了控制DIMOX工艺中复合材料的生长速度和体积,采用压差法补加合金,使剩余铝合金熔体的成分得到调整并与正在氧化生长的Al₂O₃/Al复合材料层保持连续接触。试验研究了补加合金成分对Al-3Mg-10Si合金氧化生长的影响作用。结果表明:补加纯Al或低Mg、Si含量的铝合金,能够降低合金熔体的含镁量,缩短材料生长前沿合金熔体成分到达Al₂O₃-(Al,Mg)两相区的时间,促进传质过程,加速材料生长,有利于获取较大体积的复合材料。     

Patterned silver nanoparticle films by an ion complexation process in thermally evaporated fatty acid films

The formation of silver nanoparticle films in a patterned manner on suitable substrates is described. The protocol for realising such structures comprises of the following steps. In the first step, patterned films of a fatty acid are thermally evaporated onto solid supports using suitable masks (e.g. a TEM grid). Thereafter, the fatty acid film is immersed in silver nitrate solution and Ag⁺ ions entrapped in the lipid matrix by electrostatic complexation with the carboxylate ions of the fatty acid molecules. The final step involves the reduction of the Ag⁺ ions in situ thus leading to the formation of silver nanoparticles within the patterned lipid matrix. The process of metal ion incorporation and reduction may be repeated a number of times to increase the nanoparticle density in the lipid matrix. The silver nanoparticle density may also be increased by dissolution of the fatty acid molecules in suitable solvents. The process of Ag⁺ ion entrapment and formation of silver nanoparticles within the patterned lipid matrix has been followed by quartz crystal microgravimetry, UV-VIS spectroscopy, FTIR, SEM and EDX. The process described shows immense potential for extension to assemblies of nanoparticles in more intricate patterns as well as to the growth of semiconductor quantum dots in such patterns.     

嵌有纳米碳颗粒凝胶玻璃的制备及其发光特性

以磷酸三乙酯、硝酸铝和正硅酸乙酯为原料,通过它们的水解制备了ｘＡｌ_２Ｏ_３·ｘＰ_２Ｏ₅·１００ＳｉＯ_２（ｘ＝０．２５～３）凝胶．在６００℃对凝胶进行热处理,使其中的有机基团炭化,从而制备出了镶嵌有碳纳米颗粒的ｘＡｌ_２Ｏ_３·ｘＰ_２Ｏ_５·１００ＳｉＯ_２（ｘ＝０．２５,０．５）凝胶玻璃．在室温下以５３２ｎｍ激光（Ｎｄ：ＹＡＧ）激发,在 ６３０ｎｍ处有一强的发光峰,该发光现象是由镶嵌在凝胶玻璃中的纳米碳颗粒产生的．     

Al_2O_3对稀土配合物掺杂有机改性凝胶玻璃结构及荧光性能的影响

以γ-缩水甘油氧基三甲氧基硅烷作为有机改性先驱体,采用原位合成技术,用溶胶-凝胶法制备稀土离子(Eu3+或Tb3+)、配位体β-二酮噻吩甲酰三氟丙酮或苯甲酸及协同体1,10-菲啰啉共掺的两种有机改性二氧化硅玻璃,测量它们的发射光谱和红外光谱,并进行X射线衍射分析和扫描电镜观察,探讨Al2O3的掺量对凝胶玻璃结构及性能的影响。结果表明:Al3+对稀土离子发射峰的位置没有明显的影响,并使凝胶在室温时的荧光减弱,但它能使稀土离子及原位合成的配合物在较高温度保持相对稳定,提高凝胶玻璃的热稳定性和荧光强度;在制备较实用的具有较强荧光的含稀土离子的凝胶玻璃时,要根据实际需要选取适宜掺量的Al2O3。     

成分对烧结BAS(BaAl2Si2O8)凝胶玻璃形成的影响

采用XRD、SEM和拉曼光谱研究了溶胶一凝胶法制备的接近钡长石化学计量成分的Ba0．Al2O3-SiO2系烧结玻璃形成趋势。结果表明，在本实验条件下，SiO2含量高和BaO／Al2O3比值大，有助于形成玻璃。BaO／SiO2比值大，形成[AlO4]四配位结构的A12O3含量高。BaO／Al2O3与[AlO4]／Al^3 的关系近似线性关系。建立了一个烧结BAS凝胶玻璃形成的判别式，计算了在实验成分范围内，玻璃形成区与析晶区的边界线。根据判别式得到的计算结果与实验结果相符。     

Crystallization behavior of silicon quantum dots in a silicon nitride matrix

Silicon quantum dot superlattice was fabricated by alternating deposition of silicon rich nitride (SRN) and Si3N4 layers using RF magnetron co-sputtering. Samples were then annealed at temperatures between 800 and 1,100 degrees C and characterized by grazing incident X-ray diffraction (GIXRD), transmission electron microscopy (TEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). GIXRD and Raman analyses show that the formation of silicon quantum dots occurs with annealing above 1,100 degrees C for at least 60 minutes. As the annealing time increased the crystallization of silicon quantum dots was also increased. TEM images clearly showed SRN/Si3N4 superlattice structure and silicon quantum dots formation in SRN layers after annealing at 1,100 degrees C for more than 60 minutes. The changes in FTIR transmission spectra observed with annealing condition corresponded to the configuration of Si-N bonds. Crystallization of silicon quantum dots in a silicon nitride matrix started stabilizing after 60 minutes' annealing and approached completion after 120 minutes'. The systematic investigation of silicon quantum dots in a silicon nitride matrix and their properties for solar cell application are presented.     

Flexible top-emitting organic light-emitting diodes using semi-transparent multi-metal layers

In this paper, the improved device performance of top-emitting organic light-emitting diodes (TEOLEDs) with a thin multi-metal layer stack of nickel/silver/nickel (Ni/Ag/Ni) and aluminum/silver/aluminum (Al/Ag/Al) that were used as the anode and cathode on a flexible substrate is discussed. In particular, Indium-Tin-Oxide (ITO) as an anode electrode has been used recently even though it has some problems for flexible devices. Therefore we suggested that a thin multi-metal layer electrode as a new anode is fabricated instead of ITO anode. It was verified that the ITO-free TEOLEDs showed an enhanced probability of the recombination of the electrons and holes through an improved electron/hole charge balance. We also analyzed the optical and electrical characteristics using the current density, luminance, luminance efficiency, external quantum efficiency (EQE), CIE x, y coordinates, and EL spectra of flexible TEOLED devices were characterized. ITO-free, flexible, green-emitting OLEDs with a low cost and a simple process were demonstrated.     

Synthesis of Mo(Si,Al)2 alloy by reactive hot pressing at low temperatures for a short time

Mo(Si,Al)2 alloy was prepared by reactive hot pressing at low temperatures for a short time under 20MPa in a vacuum using MoSi2, Mo and Al as starting powders. At 1160 °C, 5 min of soaking time was enough to obtain a high density alloy. At 1060 °C, however, 10min was needed. The formation of Mo(Si,Al)2 was accompanied by the melting of aluminum and controlled by the dissolution of molybdenum into the aluminum melt. It was proposed that the oxygen present in MoSi2 raw powder would react with aluminum and form Al2O3 in an amorphous or poor crystallization state. The mechanical properties of the alloy were a little stronger than those of monolithic MoSi2 alloy. The formed Al2O3 particles acted as crack-pinning elements, but a large toughening effect could not be obtained by this crack-pinning because of the strong interface bonding and the similar thermal expansion coefficients of Mo(Si,Al)2 and Al2O3.     

A study of formation and photoluminescence properties of ZnO quantum dot doped zinc-alumino-silicate glass ceramic

Transparent Al₂O₃-SiO₂-ZnO-R₂O glass ceramics were fabricated by melting method. The effects of the different kind of alkali ions on the formation of the transparent glass ceramic were studied. X-ray diffraction and high resolution transmission electron microscope were measured to study the microstructure of the samples. The results showed that, transparent glass ceramic including ZnO quantum dots was obtained after heat treatment from 700 °C to 800 °C for the sample containing K₂O. While glasses containing Li₂O and Na₂O were opal after heat treatment. Photoluminescence properties of the K₂O contained samples were studied. It was found that the photoluminescence peak shifted to longer wavelength when the heat treatment temperature and time increased, which can be ascribed to the increasing of ZnO quantum dots size.     

溶胶-凝胶法载银SiO2杂化膜的制备及性能研究

采用溶胶-凝胶法,在甲基化改性的SiO2溶胶中掺杂硝酸银,制备Ag/M-SiO2杂化膜。通过XRD、XPS、紫外-可见吸收谱、N2吸附-脱附以及气体渗透性能测试等方法,考察了银掺杂对杂化膜结构和性能的影响。结果表明,Ag/M-SiO2膜中的银元素完全为纳米金属银,具有面心立方结构。金属银的掺杂对Ag/M-SiO2膜的化学结构基本没有影响,但使其孔径和总孔体积略微增大。与未载银的SiO2膜相比,Ag/M-SiO2膜具有更大的H2渗透速率和更好的H2/CO2选择性。金属银的引入增强了H2的表面扩散作用,促进了H2在膜中的传递,提高了SiO2膜的水汽稳定性。     

Quantum efficiency and surface passivation effect of nanocrystalline Y2O3:Eu3+

Cubic nano-crystalline Y2O3:Eu3+ powders with different grain sizes were produced by chemical auto-combustion, and their structure, morphology, and fluorescent spectra were characterized. The quantum efficiency of the 5D0 level of Eu3+ was estimated, taking into account the energy transfer between Eu3+ ions located at C2 and S6 sites. Ag+ ions were introduced into the synthesis of the nanosized particles to modify the surface defects, resulting in increased emission intensity. These results indicated that the nanosized Y2O3:Eu3+ exhibits maximum internal quantum efficiency close to 90% after Ag+ ions are introduced into the synthesis of Y2O3:Eu3+. From the experimental results, it was concluded that the Ag+ ions are probably absorbed by the nanoparticle surface and do not enter the nanoparticle lattice. It was also found that the Ag+ ions can repair the surface defects and make the absorption of excitation light more efficient.     

How Effective is Plasmonic Enhancement of Colloidal Quantum Dots for Color‐Conversion Light‐Emitting Devices?

Enhancing the fluorescence intensity of colloidal quantum dots (QDs) in case of color‐conversion type QD light‐emitting devices (LEDs) is very significant due to the large loss of QDs and their quantum yields during fabrication processes, such as patterning and spin‐coating, and can therefore improve cost‐effectiveness. Understanding the enhancement process is crucial for the design of metallic nanostructure substrates for enhancing the fluorescence of colloidal QDs. In this work, improved color conversion of colloidal green and red QDs coupled with aluminum (Al) and silver (Ag) nanodisk (ND) arrays designed by in‐depth systematic finite‐difference time domain simulations of excitation, spontaneous emission, and quantum efficiency enhancement is reported. Calculated results of the overall photoluminescence enhancement factor in the substrate of 500 × 500 µm² size are 2.37‐fold and 2.82‐fold for Al ND‐green QD and Ag ND‐red QD structures, respectively. Experimental results are in good agreement, showing 2.26‐fold and 2.66‐fold enhancements for Al ND and Ag ND structures. Possible uses of plasmonics in cases such as white LED and total color conversion for possible display applications are discussed. The theoretical treatments and experiments shown in this work are a proof of principle for future studies of plasmonic enhancement of various light‐emitting materials.     

AgIn合金量子点复合玻璃的制备及光学性质研究

采用溶胶-凝胶法结合气氛控制的技术制备了AgIn合金量子点掺杂钠硼硅基(NBS)玻璃。利用X射线粉末衍射仪(XRD)、X射线光电子能谱(XPS)、高分辨透射电子显微镜(HRTEM)以及选区电子衍射(SAED)对AgIn合金量子点在玻璃中的形貌和微结构进行了表征, 并利用荧光光谱仪对该玻璃的荧光性质进行了研究。结果表明, 在600℃热处理下钠硼硅玻璃中形成了尺寸分布在5 nm左右的均一的AgIn六方晶系量子点, 而且分布在玻璃中的AgIn量子点在435 nm附近存在一个荧光峰, 表明AgIn量子点掺杂NBS玻璃可以作为激光源、非线性介质和光子设备的候选玻璃。     

Silver‐Quantum‐Dot‐Modified MoO3 and MnO2 Paper‐Like Freestanding Films for Flexible Solid‐State Asymmetric Supercapacitors

Free‐standing paper‐like thin‐film electrodes have great potential to boost next‐generation power sources with highly flexible, ultrathin, and lightweight requirements. In this work, silver‐quantum‐dot‐ (2–5 nm) modified transition metal oxide (including MoO₃ and MnO₂) paper‐like electrodes are developed for energy storage applications. Benefitting from the ohmic contact at the interfaces between silver quantum dots and MoO₃ nanobelts (or MnO₂ nanowires) and the binder‐free nature and 0D/1D/2D nanostructured 3D network of the fabricated electrodes, substantial improvements on the electrical conductivity, efficient ionic diffusion, and areal capacitances of the hybrid nanostructure electrodes are observed. With this proposed strategy, the constructed asymmetric supercapacitors, with Ag quantum dots/MoO₃ “paper” as anode, Ag quantum dots/MnO₂ “paper” as cathode, and neutral Na₂SO₄/polyvinyl alcohol hydrogel as electrolyte, exhibit significantly enhanced energy and power densities in comparison with those of the supercapacitors without modification of Ag quantum dots on electrodes; present excellent cycling stability at different current densities and good flexibility under various bending states; offer possibilities as high‐performance power sources with low cost, high safety, and environmental friendly properties.     

Aluminum elution and precipitation in glass vials: effect of pH and buffer species

Inorganic extractables from glass vials may cause particle formation in the drug solution. In this study, the ability of eluting Al ion from borosilicate glass vials, and tendencies of precipitation containing Al were investigated using various pHs of phosphate, citrate, acetate and histidine buffer. Through heating, all of the buffers showed that Si and Al were eluted from glass vials in ratios almost the same as the composition of borosilicate glass, and the amounts of Al and Si from various buffer solutions at pH 7 were in the following order: citrate?>?phosphate?>?acetate?>?histidine. In addition, during storage after heating, the Al concentration at certain pHs of phosphate and acetate buffer solution decreased, suggesting the formation of particles containing Al. In citrate buffer, Al did not decrease in spite of the high elution amount. Considering that the solubility profile of aluminum oxide and the Al eluting profile of borosilicate glass were different, it is speculated that Al ion may be forced to leach into the buffer solution according to Si elution on the surface of glass vials. When Al ions were added to the buffer solutions, phosphate, acetate and histidine buffer showed a decrease of Al concentration during storage at a neutral range of pHs, indicating the formation of particles containing Al. In conclusion, it is suggested that phosphate buffer solution has higher possibility of forming particles containing Al than other buffer solutions.     

Structure and optical properties of AlxZn1−xO alloys by sol-gel technique

Al_xZn_1−xO (x = 0-0.5) thin films were prepared on quartz glass substrates by sol-gel technique. X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were employed for microstructure characterization of these thin films. In films with up to 20 at.% Al incorporation, compound nano-crystal phase was observed while wurtzite structure disappeared. Zn3d electron binding energy and Zn LMM‘s chemical shift were both increased by more than 0.4 eV. Transmittance spectra revealed that these films possessed high transmittance in the visible region, and the end of UV absorption edge shifted to less than 300 nm when Al content exceeds 20 at.% due to quantum confinement effect.