金纳米薄膜的荧光光谱特性

采用电化学方法制备了胶体盒纳米球状颗粒,并利用自组装方法在石英玻璃村底上镀制了金纳米薄膜。在室温下测得其紫外-可见吸收光谱和荧光发射光谱。在吸收光谱中观察到两个吸收峰,其中610nm、处的吸收峰来源于凝聚金纳米颗粒纵向的表面等离子体共振。在荧光发射光谱中也观察到与纵向表面等离子体共振有关的长波段的发射峰。增加激励光强度或增加薄膜中金粒子散密度都将导致新荧光发射峰的产生．这表明金纳米薄膜中存在循环多重散射,并由此引发了荧光发射峰数目和强度的变化。     

紫外-可见光光束在TiO_2纳米颗粒胶体中的传输（英文）

紫外光诱导纳米颗粒胶体射流加工技术利用紫外光场对入射纳米颗粒的催化作用实现对工件表面材料的高效去除。为掌握紫外光诱导纳米颗粒胶体射流加工过程中紫外光束在纳米二氧化钛胶体中的传输特性,基于纳米二氧化钛胶体对紫外-可见光的吸收及散射理论,通过系列实验得到紫外-可见光束在不同浓度、吸收层厚度的二氧化钛纳米颗粒胶体中的传输特性及衰减关系。结果表明,为保证足够强度的紫外光能通过纳米二氧化钛胶体照射在工件表面,胶体浓度宜控制在500mol/m3以下,光-液耦合区胶体吸收层的厚度不宜超过20mm。     

紫外-可见光光束在TiO2纳米颗粒胶体中的传输

紫外光诱导纳米颗粒胶体射流加工技术利用紫外光场对入射纳米颗粒的催化作用实现对工件表面材料的高效去除。为掌握紫外光诱导纳米颗粒胶体射流加工过程中紫外光束在纳米二氧化钛胶体中的传输特性,基于纳米二氧化钛胶体对紫外-可见光的吸收及散射理论,通过系列实验得到紫外-可见光束在不同浓度、吸收层厚度的二氧化钛纳米颗粒胶体中的传输特性及衰减关系。结果表明,为保证足够强度的紫外光能通过纳米二氧化钛胶体照射在工件表面,胶体浓度宜控制在500 mol/m3以下,光-液耦合区胶体吸收层的厚度不宜超过20 mm。     

CdS及其包裹型纳米颗粒PVA基复合膜的特性研究

以聚乙烯醇 (PVA)、六偏磷酸钠为分散剂 ,采用溶胶法合成了 Cd S纳米胶体颗粒 ,制备出 Cd S及其包裹型纳米颗粒 PVA基复合膜。通过光子相干光谱粒度仪 (PCS)、紫外 -可见吸收光谱 (UV- VIS)、荧光光谱 (PL)对样品进行了初步表征。结果表明 ,Cd S纳米颗粒 PVA基复合膜的紫外 -可见吸收光谱有明显的蓝移现象 ,所发荧光主要由表面态发射引起 ;包裹型 PVA基复合膜所发荧光主要由带边发射引起     

纳米ZnO胶体可见发射机制的研究

关于ZnO可见发射机制的讨论目前尚无定论。本文研究了不同颗粒尺寸的纳米晶ZnO胶体的发射性质,观测到两个发射带,其中之一是激子发射,另一个是可见发射;发现两个发射带的峰值能量之间存在线性关系,并由此提出了可见发射机制是来自导带的电子到深陷阱的跃迁。     

纳米银粒子的发光特性研究

研究了不同粒径和表面修饰的纳米银粒子的发光特性.研究结果表明,在不同波长光激发下,纳米银粒子在362 nm附近出现较强的发射峰,592和725 nm附近出现较弱的发射峰.随着激发光波长增加,发射峰强度下降,362 nm附近的发射峰红移.纳米银颗粒对210 nm的激发光最为敏感.发射峰波长与纳米银粒子表面修饰状态和颗粒尺寸关系不大,只是随着颗粒尺寸的减小,发射峰强度下降.随着狭缝宽度的减小,发射峰强度下降.随着纳米银胶浓度减少,发射峰逐渐聚拢合并为426 nm的单峰,且发射峰的强度先增强后逐渐下降.通过纳米银粒子表面光电子的吸收-再发射和表面能级杂化探讨了纳米银粒子的发光机理.     

激光刻蚀银纳米粒子岛膜的SERS特性

利用激光刻蚀的方法,通过改变激光脉冲的能量,制备出一系列的纳米金属银胶体。将银胶体沉积在铝基底上形成一层银岛膜。用紫外—可见吸收光谱、SEM及拉曼光谱对银胶体和银岛膜进行了表征。研究结果表明,刻蚀所用激光脉冲的能量影响胶体中银颗粒的分布;不同能量下制备的胶体所形成的银岛膜具有不同的表面增强效果;该岛膜具有增强效果优异、制备简便等特点。     

激光刻蚀法制备Pd纳米颗粒及其光谱特性初探

用Nd:YAG脉冲激光器1 064 nm激发光在二次去离子水中制备了Pd胶体.此体系中Pd颗粒表面不存在杂质离子,为"化学纯净".刻蚀后将Pd胶体沉积在铝基底上形成一层Pd岛膜.紫外-可见吸收光谱表明Pd胶体在200～800 nm测量范围内没有出现特征吸收峰,说明Pd胶体的吸收光谱并不能反映Pd胶体中Pd颗粒的粒径分布等信息.SEM显示Pd岛膜由Pd纳米颗粒组成,其平均粒径在200 nm左右.以101-3mo/·L-1的4-巯基吡啶(4MPY)为探针分子对Pd胶体和Pd岛膜的表面增强拉曼散射(SERS)进行了研究.结果显示,在Pd胶体中没有获得4MPY的SERS信号;Pd岛膜是一种非常高效的活性增强基底,从实验数据估算得出其增强因子约为8.7×104.SERS光谱分析显示4MPY分子通过S原子以倾斜的方式吸附于Pd岛膜表面;与Pd岛膜表面相比,4MPY分子在Ag岛膜上更趋于采用垂直于表面的吸附取向.     

电解质浓度对胶体粒子表面有效电荷的影响

胶体粒子的表面有效电荷是决定胶体性质的重要物理量,但溶液环境(如电解质溶液浓度)是否影响其数值至今尚无统一认识,近年来的一些研究工作给出了存在争议的不同结果和假设.在直接实验测量方面,由于电解质离子和胶体表面吸附离子的置换,粒子表面基团的不完全电离和胶体粒子对离子吸附的共同作用,使得对这类粒子在不同溶液环境下的表面有效电荷的测量和变化机理的认识极为困难.针对该问题,本文测定了羧基和磺酸基修饰的聚苯乙烯胶体颗粒在不同粒子浓度和HCl浓度下的电导率,由于两种粒子与HCl电离产生的阳离子相同(均为H+),可根据电导率-数密度法(迁移法)得到胶体颗粒表面有效电荷数.通过实验结果分析,明确了HCl浓度以及粒子数密度对胶体粒子表面电荷的影响规律以及表面电荷随HCl浓度增大的原因.除此之外,羧基修饰颗粒比磺酸基修饰颗粒的表面电荷随HCl浓度变化更快;对于同一HCl浓度,磺酸基修饰胶体表面电荷不受粒子数密度影响,而羧基修饰胶体颗粒却与之相关.基于粒子表面电荷的理论模型,对这些问题都给出了相应的解释.     

基于微陷阱结构的金属二次电子发射系数抑制研究

近年来,金属二次电子发射系数的抑制研究在加速器、大功率微波器件等领域得到了广泛关注.为评估表面形貌对抑制效果的影响,利用唯象概率模型计算方法对三角形沟槽、矩形沟槽、方孔及圆孔4种不同形状微陷阱结构的二次电子发射系数进行了研究,分析了微陷阱结构的形状、尺寸对二次电子发射系数抑制特性的影响规律.理论研究结果表明:陷阱结构的深宽比、孔隙率越大,则其二次电子发射系数抑制特性越明显;方孔形和圆孔形微陷阱结构的二次电子发射系数抑制效果优于三角形沟槽和矩形沟槽;具有大孔隙率的微陷阱结构表面的二次电子发射系数对入射角度的依赖显著弱于平滑表面.制备了具有不同表面形貌的金属样片并进行二次电子发射系数测试,所得实验规律与理论模拟规律符合较好.     

BiI3层状半导体超微粒子的光学性质

本文研究了BiI3半导体溶胶的光学性质.进一步证实,在BiI3胶体样品中,真实的BiI3半导体微晶粒予的吸收被强的I3-离子吸收掩盖了.通过测量激发光谱,确定了BiI3微晶的吸收位置.用光谱数据计算得到的尺寸分布与电镜结果和理论分析符合得很好.得到的结果表明,BiI3胶体中的BiI3微晶与体材料相比。存在着显著的量子尺寸效应.     

Observation of band gap and surface defects of ZnO nanoparticles synthesized via hydrothermal route at different reaction temperature

The effects of reaction temperature on the average particle size, surface defects and band gap of ZnO nanoparticles have been systematically investigated. The hydrothermal method was employed to synthesize ZnO nanostructures. The nanostructures of the resultant ZnO were studied by means of X-ray diffraction, Transmission Electron Microscopy, Ultraviolet-visible absorption, Raman, Fourier transform Infra-red and Photoluminescence spectroscopy. With increase in the reaction temperature, the peak position of the ultraviolet emission shifts slightly towards the red wavelength and the crystal quality was improved. The prepared ZnO nanoparticles have residual intermediate compound on the surface in the form of an acetate group, which acts as defect centers for the emission of yellow emission. Spectra analyses show that the visible emission depends strongly on the preparation conditions.     

Surface modification of ZnO nanocrystals

Nano-crystalline ZnO particles were synthesized using alcoholic solutions of zinc acetate dihydrate through a colloidal process. Five types of capping agents: 3-aminopropyl trimethoxysilane (Am), tetraethyl orthosilicate (TEOS), mercaptosuccinic acid (Ms), 3-mercaptopropyl trimethoxysilane (Mp) and polyvinylpyrrolidone (Pv) were added at the first ZnO precipitation time (first PPT) to limit the particle growth. The first three capping agents effectively capped the ZnO nanoparticles and limited the growth of the particles, while the last two capping agents caused agglomeration or larger clusters in the solutions. Particles synthesized were in the size range of 10-30 nm after capping, and grew to 60 and 100 nm in 3 and 6 weeks, respectively, during storage at ambient conditions. Refluxing time was found to only affect the first PPT time. Washing by ethanol and slow drying were very important in converting Zn(OH)₂ into ZnO. XRD analyses revealed single phase ZnO Wurtzite crystal structure. Photoluminescence (PL) spectra showed high-intensity in UV emission and very low intensity in the visible emission, which indicates a good surface morphology of the ZnO nanoparticles with little surface defects. Optical absorption spectra showed a blue shift by the capped ZnO due to the quantum confinement effect by the single crystal size of 5-6 nm as analysed by TEM. Capping effectiveness of each agent is discussed through possible capping mechanism and chemical reaction of each capping agent. This synthesis process is a low cost, high purity, easy to control method using only bio-compatible materials.     

溶胶-凝胶制备ZnO-SiO2复合膜的量子效应和上转换发光

采用溶胶-凝胶技术在玻璃衬底上制备了ZnO薄膜和ZnO-SiO₂复合膜.原子力显微镜照片显示ZnO薄膜具有球状纳米晶粒；可见光-紫外透射光谱表明ZnO-SiO₂复合膜在可见光区的透过率大约是85%，透过率从330 nm开始下降，到290 nm附近降为零.由于量子效应，吸收边出现明显的蓝移.在室温下用不同波长的光激发ZnO-SiO₂复合膜，光致发光谱显示ZnO-SiO₂复合膜对应于激子发射的290 nm附近的紫外发光峰与透射谱所显示的吸收边位置一致，没有出现斯托克斯红移.同时，ZnO-SiO₂复合膜出现了双光子和三光子吸收现象和上转换发光现象. 关键词： 2')" href="#">ZnO-SiO₂ 量子效应 双光子和三光子吸收 上转换发光     

球形ZnO的微波辅助合成及光谱研究

以Zn(NO₃)₂为原料,CO(NH₂)2为沉淀剂,加入表面活性剂甲基丙烯酸甲酯,经微波加热制备获得颗粒尺度为亚微米级的ZnO.采用X射线衍射(XRD)、扫描电镜(SEM)研究了制备条件对样品结构、形貌的作用;PL方法讨论了其荧光发光光谱.发现采用微波加热法获得的ZnO呈球形,尺度在100nm左右,相比较,传统高温加热获得的样品呈c轴优先取向的短棒状.讨论认为,由于微波辅助方法能够使前驱物温度梯度变化小,表面Zn²⁺,O²⁺析出均匀,因此有助于获得球形的粉末粒子.     

Optical characterization of ZnO nanoparticles capped with various surfactants

The presence of surfactants (Hexamine, tetraethylammonium bromide (TEAB), cetyltrimethylammonium bromide (CTAB), tetraoctylammonium bromide (TOAB) and PVP) on the surface of zinc oxide (ZnO) nanoparticles resulted variation in their optical properties. The optical properties of each surfactant-capped zinc oxide nanoparticles were investigated using UV-visible absorption and fluorescence techniques. The particle size of these nanoparticles were calculated from their absorption edge, and found to be in the quantum confinement range. The absorption spectra and fluorescent emission spectra showed a significant blue shift compared to that of the bulk zinc oxide. Large reduction in the intensity of visible emission of zinc oxide/surfactant was observed and these emissions were vanished more quickly, with the decrease in excitation energy, for the smaller nanoparticles. Out of the four surfactants (other than PVP), CTAB-capped zinc oxide has smallest particle size of 2.4 nm, as calculated from the absorption spectrum. Thus the presence of surfactant on the surface of zinc oxide plays a significant role in reducing defect emissions. Furthermore, ZnO/PVP nanoparticles showed no separate UV emission peak; however, the excitonic UV emission and the visible emission at 420 nm overlap to form a single broad band around 420 nm.     

Formation of ZnO@Cd(OH)2 core-shell nanoparticles by sol-gel method: An approach to modify surface chemistry for stable and enhanced green emission

We report the formation of highly stable and luminescent ZnO@Cd(OH)₂ core-shell nanoparticles by simple introduction of cadmium salt in the initial precursor solution, used to synthesize ZnO nanoparticles by sol-gel route. The cadmium to zinc salt concentration ratio has been also varied to control the growth of ZnO nanoparticles at the smaller particle size. Formation of ZnO@Cd(OH)₂ core-shell nanostructure has been confirmed by X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). UV-vis absorption spectroscopy exhibits blue-shift in absorption edge on increasing cadmium concentrations. The photoluminescence emission spectra showed the remarkably stable and enhanced visible (green) emission from suspended ZnO@Cd(OH)₂ nanoparticles in comparison to bare ZnO nanoparticles. It is postulated that Cd(OH)₂ layer at the surface of ZnO nanoparticles prevents the agglomeration of nanoparticles and efficiently assists the trapping of hole at the surface site, a first step necessary for visible emission. The Fourier transform infrared spectroscopy (FTIR) also supports our assumption about surface chemistry.     

Size-dependent visible photoluminescence from ZnO nanoparticles prepared via SiO2 network

This study reports a simple method for the synthesis of different size of wurtzite ZnO nanoparticles in assistance of tetraethyl orthosilicate (TEOS). With the increase of the amount of TEOS added, the average size of ZnO nanoparticles was found decreased from ∼14.6 to ∼1.9 nm by characterization of X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The growth of ZnO nanoparticles is proposed to be controlled by the density of the SiO₂ chain mesh which is determined by TEOS amount in precursor. Ultraviolet–visible (UV–VIS) absorption and photoluminescence (PL) spectra show both shift to higher energy in cut-off edge and in visible emission bands respectively. The electron transition process in the mechanism of the visible emission shift was described and related to quantum size effect in ZnO nanoparticles.     

Ultrasonic induced photoluminescence decay in sonochemically obtained cauliflower-like ZnO nanostructures with surface 1D nanoarrays

Cauliflower-like ZnO nanostructures with average crystallite size of about 55 nm which have surface one dimensional (1D) nanoarrays with 10 nm diameter were successfully fabricated through a simple sonochemical route. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and room temperature photoluminescence (PL) characterizations were performed to investigate the morphological and structural properties of the obtained nanostructures. It has been shown that the synthesized cauliflower-like ZnO nanostructures irradiated UV luminescence and a green peak in visible band. Ultrasonic post-treatment of the particles for about 2 h increased the density of surface defects resulted in an increase in the green emission intensity.