High UV absorption efficiency of nanocrystalline ZnO synthesized by ultrasound assisted wet chemical method

Ultrasound assisted wet-chemical method has been carried out to incorporate different metal and non-metal ions such as; Li, S and Ag into ZnO. Characteristic studies on the structural and optical properties of the samples especially; the ultra-violet (UV) light absorption have been carried out. X-ray diffraction (XRD) analysis shows the formation of hexagonal crystal structure of ZnO along with changes in crystallinity and micro-strain with impurity doping. The morphology of the doped samples changes from particle like structure to flower and rod like structures showing the influence of dopant ions on nano ZnO growth. Infra-red (IR) transmittance spectra give information about the presence of metal–oxygen bond along with other stretching and bending modes. UV–visible absorption studies show the narrowing and sharpening of UV absorption band along with a blue shift for the doped samples. This shows the intensification in the excitonic absorption in ZnO after doping specific elements which will find application in UV blocking agents. Photoluminescence (PL) measurement shows the presence of excitonic emission and emissions due to intrinsic defects and external impurities in UV and visible regions respectively. These emission bands show a change in their position and intensity which has been explained on the basis of the existence of impurity levels in the band gap of ZnO.     

Magnetic and electronic properties of nanocrystalline Gd3Fe5O12 garnet

The Gd₃Fe₅O₁₂ nanocrystalline Gadolinium Iron Garnet (GdIG) obtained from a sintered block was milled in a high energy ball mill. We measured the magnetization at 5 K under applied fields up to 12 T. We report here our study of approach to saturation magnetization. The results have been interpreted within the framework of random anisotropy model. From an analysis of the approach to saturation magnetization some fundamental parameters have been extracted. We have determined the anisotropy field H_r and the local magnetic anisotropy constant K_L. In addition, first-principles spin-density functional calculations, using the Full potential Linear Augmented Plane Waves (FLAPW) method are performed to investigate electronic and magnetic structures. All computed parameters are discussed and compared to available experimental data.     

Tuning the cathodoluminescence of porous silicon films

We have obtained intense cathodoluminescence (CL) emission from electron beam modified porous silicon films by excitation with electrons with kinetic energies below 2 keV. Two types of CL emissions were observed, a stable one and a non-stable one. The first type is obtained in well-oxidized samples and is characterized by a spectral peak that is red shifted with respect to the photoluminescence (PL) peak. The physically interesting and technologically promising CL is however the CL that correlates closely with the PL. Tuning of this CL emission was achieved by controlling the average size of the nanostructure thus showing that the origin of this CL emission is associated with the quantum confinement and the surface chemistry effects that are known to exist in the porous silicon system. We also found that the electron bombardment causes microscale morphological modifications of the films, but the nanoscale features appear to be unchanged. The structural changes are manifested by the increase in the density of the nanoparticles which explains the significant enhancement of the PL that follows the electron irradiation.     

纳米晶ZrO2∶Dy3+的制备与发光性质研究

利用共沉淀法制备了纳米晶ZrO2∶Dy3+发光粉体,对不同掺杂浓度、不同煅烧温度的系列样品,均观测到Dy3+离子的室温强特征发射.样品的晶相与发射性质的研究表明:所制备的样品经600℃~950 ℃热处理后,晶相经历从四方相到以单斜相为主的变化;由于晶相的变化,发现有两个发光中心,分别位于四方相和单斜相.激发Dy3+的6P7/2能级,当稀土离子处在四方相(格位一)时有利于483 nm和583 nm的发射,当稀土离子处在单斜相(格位二)时有利于490 nm和577 nm的发射.基质ZrO2和Dy3+离子之间有能量传递,950℃时能量传递效果最好.荧光强度与掺Dy3+离子浓度关系表明,Dy3+在纳米晶ZrO2中的最适合掺杂浓度与ZrO2的晶相有关,四方相时,最适合掺杂浓度为0.5%,混合相时为1%.     

Investigation into the photo-induced change in wettability of hydrophobized TiO2 films

The photo-induced change in wettability of hydrophobized TiO₂ films has been investigated for steel coated with acidic TiO₂ nanosols containing varying concentrations of dispersed nanocrystalline titania, such as Degussa P25. The photo-induced change in wettability was evaluated by measuring the time-dependent drop of water contact angle (WCA) after samples had been soaked in either n-octyltriethoxysilane (OTS) or decanoic acid (DA). TiO₂ films treated in this way exhibit superhydrophobic behaviour, with WCA greater than 160°. After radiation with UV (black light), the superhydrophobic properties are transformed into superhydrophilic properties, with WCA of almost 0°. As P25 content and layer thickness increase, high rates of photo-induced change are found, but a moderate calcination regime is required. On the other hand, hardness and E modulus pass through a maximum at 25 wt% P25, so that a P25 content between 25 and 50 wt% is the optimum for practical uses. With such stable coatings, wettability can be controlled over a wide range, and the switch between hydrophobic and hydrophilic states can be carried out repeatedly when DA is used as the hydrophobizing agent. Use of a low calcination temperature (450 °C) for the intermediate annealing of the single layers in multilayer coatings and a short final sintering step at a relatively high temperature (e.g. 630 °C for 10 min) allow the preparation of relatively thin TiO₂ films on steel with a high photoactivity.     

Rare-earth iron-based intermetallic compounds and their carbides: Structure and magnetic behaviors

The structural and magnetic properties of Sm₂Fe_17-xMo_x, its out of equilibrium precursor SmFe_9-yMo_y and their carbides are investigated by means of powder X-ray diffraction, magnetic measurements and high-resolution transmission electron microscopy. The structure of the nanocrystalline Sm_1-s(Fe,Mo)_5+2s alloys are governed by the s Sm vacancy rate and the x amount of Mo. In this work, the Rietveld analysis shows that for s=0.33 the structure is of Th₂Zn₁₇-type and P6/mmm with the stoichiometry 1/9 for s=0.36. Moreover, it points out a lattice expansion along the c-axis after Mo substitution for Fe and reveals a 6c preferential occupation for Mo atoms in structure, and 2e for the out of equilibrium hexagonal precursor. Upon carbon insertion, the lattice expansion favors the Curie temperature increase up to 35% for Sm₂Fe_16.42Mo_0.58C₂ and 49% for the metastable SmFe_8.7Mo_0.3C carbide. The Curie temperature and the coercive field of the 1/9 carbides are higher than those of 2/17 ones. This makes the out of equilibrium hexagonal precursor a competitive candidate for use as permanent magnet.     

CoFe2-xRExO4(RE=Tb,Dy)纳米晶薄膜的化学合成及磁性

以溶胶-凝胶法制备了稀土铽或镝掺杂的钴尖晶石铁氧体纳米晶薄膜.考察了Tb或Dy的掺杂量及晶化条件对晶相的影响.结果表明,稀土离子的掺杂量x超过0.3时,样品很难形成尖晶石单相.原子力显微镜对纳米晶薄膜表面形貌的观测显示,溶胶-凝胶法制备的薄膜粒度可控制在20～50nm,且具有较高的表面平整度.对于厚度为200nm的薄膜,均方根粗糙度仅为4～5nm.磁特性研究发现,掺杂Tb或Dy的样品矫顽力明显提高.     

在纳米晶Co－Mo／Ni复合电极上的析氢反应

采用复合电镀的方法将不同球磨时间制备的高催化活性的纳米晶Ｃｏ－Ｍｏ合金粉直接镀在电极表面,用稳态极化曲线及交流阻抗技术测试了这些电极析氢的电化学活性,并用Ｘ射线衍射、透射电镜及Ｘ射线光电子能谱、扫描电镜监测了Ｃｏ－ＭＯ合金粉的物相结构、晶粒尺寸和复合镀层的成份、形貌,实验结果表明,Ｃｏ－Ｍｏ纳米晶合金粉有较高的析氢催化活性。球磨使钴钼粉合金化成为纳米晶,一方面增加了复合镀层的真实表面积,另一方面由于纳米晶合金具有高比例的表面活性原子,致使析氢活化能降低,加快了析氢反应,研究表明在不太高温度下,电化学脱附的活化能和整个析氢反应的活化能一致。说明电化学脱附为速度控制步骤。     

Magneto recyclable,green fabricated Fe3O4 nanorods on photo responsive of textile dye degradation and identification products by LC-MS

Prior to being released towards water sources such as rivers, lakes, and groundwater, the efficient technique of removing color out textile effluents seems to have become widely used. Such contaminants are extremely difficult for traditional wastewater treatment methods to completely eliminate. This innovative development of phytonutrients uses Fe₃O₄ nanorods, that have been employed as photocatalytic to change substrate colors in the aqueous layer when exposed to light. Given prominence was adopted to incorporate phytonutrients with Fe3O4 nanorods. The degradation of the methyl violet colour has been acknowledged by the depletion of the UV light (UV) absorption edge that also originated at 581 nm. The significant colour expulsion of the Fe3O4 nanorod was proved to really be 97% after 60 min. The findings demonstrate that ecologically responsible Fe₃O₄ nanorods are immensely beneficial in the photocatalytic reaction of harmful pollutants.