用巯基乙酸作稳定剂制备CdSe纳米晶的光学性质

以巯基乙酸为稳定剂制备了CdSe纳米晶，通过尺寸选择沉淀得到2nm到3nm之间不同尺寸的纳米晶，利用室温光吸收，光致发光（PL）和光致发光激发（PLE）谱来研究了CdSe纳米团簇的光学性质。紫外－可见吸收谱给了具有清晰激光特征的尖锐吸收边，这表明样品的尺寸分布很窄。光致发光研究表明，样品有两个发射带，一个具有较高能量位于吸收边，来自电子－空穴对从最低激发态能级弛豫后的辐射复合，另一个低能发射带归属于基质与纳米晶界面存在的俘获中心。PLE谱中有2个吸收带，分别是S－S和P－P跃迁。最后还给出了不同激发能量下的发光特性。     

Photoluminescence of Si-based nanotips fabricated by anodic aluminum oxide template

Large-area, high-density silicon-based nanotips were fabricated using electrochemical lithography. The morphology and optical properties of the samples were characterized by atomic force microscopy and photoluminescence. The distribution and size of the silicon-based nanotips were uniform. Two photoluminescence peaks were observed at 585 and 620 nm. The peak centered at 585 nm exhibited a narrow full-width at half maximum. No evident peak energy shift was observed when the measurement temperature was increased from 10 K to room temperature, which suggested that the photoluminescence should be attributed to the interface states and/or defects in the silicon-based nanotips.     

Effect of doping and annealing on the physical properties of ZnO:Mg nanoparticles

Well-dispersed undoped and Mg-doped ZnO nanoparticles with different doping concentrations at various annealing temperatures are synthesized using basic chemical solution method without any capping agent. To understand the effect of Mg doping and heat treatment on the structure and optical response of the prepared nanoparticles, the samples are characterized using X-ray diffraction (XRD), energy-dispersive X-ray (EDX), UV–Vis optical absorption, photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The UV–Vis absorbance and PL emission show a blue shift with increasing Mg doping concentration with respect to bulk value. UV–Vis spectroscopy is also used to calculate the band-gap energy of nanoparticles. X-ray diffraction results clearly show that the Mg-doped nanoparticles have hexagonal phase similar to ZnO nanoparticles. TEM image as well as XRD study confirm the estimated average size of the samples to be between 6 and 12 nm. Furthermore, it is seen that there was an increase in the grain size of the particles when the annealing temperature is increased.     

Synthesis of stable dispersion of ZnO quantum dots in aqueous medium showing visible emission from bluish green to yellow

Aqueous dispersion of 4-8 nm size stable ZnO quantum dots (QDs) exhibiting luminescence in the visible region have been synthesized by a simple solution growth technique at room temperature. Silica has been used as capping agent to control the particle size as well as to achieve uniform dispersion of QDs in aqueous medium. X-ray diffractometer (XRD) analysis reveals formation phase pure ZnO particles having wurzite (hexagonal) structure. Atomic force microscope (AFM) images show that the particles are spherical in shape, having average crystalline sizes ∼4, 5.5 and 8 nm for samples prepared at pH values of 10, 12 and 14, respectively. From the optical absorption studies, the band gap energy of QDs is found to be blue shifted as compared to bulk ZnO (3.36 eV) due to the quantum confinement effect and is consistent with the band gap calculated by using effective-mass approximation model. The photoluminescence (PL) observed in these QDs has been attributed to the presence of defect centers.     

Stability, size and optical properties of silver nanoparticles prepared by laser ablation in different carrier media

We studied the effects of the surrounding liquid environment on the size and optical properties of silver nanoparticles prepared by laser ablation by a pulsed Nd:YAG laser operated at 1064 nm. The silver targets used were kept in acetone, water and ethanol. TEM observations and optical extinction were employed for characterization of particle size, shape and optical properties, respectively. Nano silver in acetone showed a narrow size distribution with a mean size of 5 nm and the colloidal solution was stable. In deionised water a rather narrow size distribution with a mean size of 13 nm was observed and nanoparticles were precipitated slowly after about two weeks. In ethanol, a broadening in size distribution and optical extinction spectra was observed. Silver nanoparticles in ethanol with a mean size of 22 nm were completely precipitated after 48 h. In acetone, deionised water and ethanol, the wavelengths of maximum optical extinction are 399, 405 and 411 nm respectively, which is attributed to increasing the size of the nanoparticles. Growth, aggregation and precipitation mechanisms were related to the dipole moment of the surrounding molecules in order to clarify the difference in size, optical properties and stability of the nanoparticles. PACS 79.20.Ds; 81.07.-b; 61.46.+w     

Photoluminescence properties of a single tapered CuO nanowire

Photoluminescence spectroscopy has been employed in order to explore the optical emission properties of a single CuO nanowire, grown on a copper grid in static air by simple thermal oxidation method. As the diameter of the single tapered CuO nanowire decreases, the green emission of the nanowire gradually shifts towards the higher energy side. A steady blue shift of 20 nm of the photoluminescence (PL) peak has been attributed to nanosize effect. Higher surface to volume ratio and enhanced surface defects along the growth direction of the nanowire might be responsible for the observed PL behavior. In addition, crystallization process along the length of the nanowire during growth to form pure CuO structure from the precursor state may also have some role in observed shift in the PL peak.     

制备水溶性CdS量子点的一种物理方法：飞秒激光烧蚀法

用Ti/sapphire飞秒激光系统产生的100fs、800nm激光对置于水中的CdS体相材料进行烧蚀,得到了水溶性CdS纳米粒子。这种纯物理过程保证了无污染的制备环境,从而保证了所合成材料的纯洁性。通过透射电子显微镜、紫外/可见/近红外吸收光谱、室温光致发光谱的方法对CdS量子点的形貌及其光学性质进行了表征。结果表明:利用飞秒激光烧蚀法所制备的CdS量子点可直接分散在水中而且具有粒径小、分布均匀的特点;同时具有较好的胶体稳定性,可在空气中稳定存放6个月以上。飞秒激光烧蚀法所制备的CdS量子点所具有的这些性质使其在生物标记领域引起极大的兴趣,而且也为纳米材料的制备提供了新的思路。     

Mechanical behavior of silicon carbide nanoparticles under uniaxial compression

The mechanical behavior of SiC nanoparticles under uniaxial compression was investigated using an atomic-level compression simulation technique. The results revealed that the mechanical deformation of SiC nanocrystals is highly dependent on compression orientation, particle size, and temperature. A structural transformation from the original zinc-blende to a rock-salt phase is identified for SiC nanoparticles compressed along the [001] direction at low temperature. However, the rock-salt phase is not observed for SiC nanoparticles compressed along the [110] and [111] directions irrespective of size and temperature. The high-pressure-generated rock-salt phase strongly affects the mechanical behavior of the nanoparticles, including their hardness and deformation process. The hardness of [001]-compressed nanoparticles decreases monotonically as their size increases, different from that of [110] and [111]-compressed nanoparticles, which reaches a maximal value at a critical size and then decreases. Additionally, a temperature-dependent mechanical response was observed for all simulated SiC nanoparticles regardless of compression orientation and size. Interestingly, the hardness of SiC nanocrystals with a diameter of 8 nm compressed in [001]-orientation undergoes a steep decrease at 0.1–200 K and then a gradual decline from 250 to 1500 K. This trend can be attributed to different deformation mechanisms related to phase transformation and dislocations. Our results will be useful for practical applications of SiC nanoparticles under high pressure.     

Preparation and properties of semiconductor CuO nanoparticles via a simple precipitation method at different reaction temperatures

Preparation and properties of CuO nanoparticles as an important p-type semiconductor via a simple precipitation method at different reaction temperatures varying from 10 to 115°C using copper acetate as a starting material have been reported. In addition, we investigated the influence of the ultrasonic irradiation through synthesizing the nanosized CuO at 60°C. Samples were characterized by XRD, FT-IR, SEM, TEM and UV-Vis techniques. XRD patterns of samples were identical to the single-phase pure CuO with a monoclinic structure. FT-IR spectra exhibited sharp peaks at around 519 and 598?cm^?1 which can be assigned to vibrations of the Cu-O bond. Results indicated that properties of samples had great dependence on the temperature and ultrasonic irradiation. The crystallite size and crystallization increased with increasing the temperature from 10 to 115°C. The band gap of samples was estimated to be in the range of 1.9–2.9?eV that is larger than the reported value for the bulk CuO (1.85?eV). This study provides a simple method for the preparation of nanosized CuO with a better surface uniformity and a narrow size distribution. Synthesized CuO samples with adjustable and controllable optical properties make the applicability of copper oxide even more versatile.     

Characterization of ZnS nanoparticles synthesized by co-precipitation method

ZnS nanoparticles are prepared by homogeneous chemical co-precipitation method using EDTA as a stabilizer and capping agent. The structural, morphological, and optical properties of as-synthesized nanoparticles are investigated using x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible(UV-Vis)absorption, and photoluminescence spectroscopy. The x-ray diffraction pattern exhibits a zinc-blended crystal structure at room temperature. The average particle size of the nanoparticles from the scanning electron microscopy image is about50 nm. The ultraviolet absorption spectrum shows the blue shift in the band gap due to the quantum confinement effect.The photoluminescence spectrum of Zn S nanoparticles shows a blue visible spectrum.     

Optical studies of samarium-doped fluoride nanoparticles

Samarium-doped calcium fluoride (CaF₂) nanoparticles were synthesized by the co-precipitation method and characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), optical absorption and photoluminescence (PL) techniques. The PXRD patterns confirmed the cubic crystallinity of the synthesized nanoparticles. The average particle size estimated using Scherer's formula was ～20?nm. The purity of the synthesized nanoparticles was confirmed by the FTIR spectrum. The morphological features studied using SEM revealed that the nanoparticles were agglomerated and porous. The optical absorption spectrum showed a strong and prominent absorption peak at ～264?nm and a weak one at ～212?nm. The PL spectrum showed broad and prominent emissions with peaks at ～387 and 532?nm along with weak emissions at 573 and 605?nm.     

Optical properties of silicon nanoparticles synthesized via electrical spark discharge in water

In this paper, we report a simple and low-cost technique for fabrication of silicon nanoparticles via electrical spark discharge between two plane silicon electrodes immersed in deionized water (DI). The pulsed spark discharge with the peak current of 60 A and a duration of a single discharge pulse of 60 μs was used in our experiment. The structure, morphology, and average size of the resulting nanoparticles were characterized by means of X-Ray Diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). TEM images illustrated nearly spherical and isolated Si nanoparticles with diameters in the 3–8 nm range. The Raman peaks of the samples were shifted to the lower wave numbers in comparison to this of bulk crystalline silicon indicating the existence of tiny particles. The optical absorption spectrum of the nanoparticles was measured in the violet–visible (UV–Vis) spectral region. By measuring of the band gap we could estimate the average size of the prepared particles. The silicon nanoparticles synthesized exhibited a photoluminescence (PL) band in the violet-blue region with a double peak at around 417 and 439 nm. It can be attributed to oxide-related defects on the surface of silicon nanoparticles, which can act as the radiative centers for the electron-hole pair recombination.     

Photochemical Characterization of Up-Converting Inorganic Lanthanide Phosphors as Potential Labels

We have characterized commercially available up-converting inorganic lanthanide phosphors for their rare earth composition and photoluminescence properties under infrared laser diode excitation. These up-converting phosphors, in contrast to proprietary materials reported earlier, are readily available to be utilized as particulate reporters in various ligand binding assays after grinding to submicron particle size. The laser power density required at 980 nm to generate anti-Stokes photoluminescence from these particulate reporters is significantly lower than required for two-photon excitation. The narrow photoluminescence emission bands at 520–550 nm and at 650–670 nm are at shorter wavelengths and thus totally discriminated from autofluorescence and scattered excitation light even without temporal resolution. Transparent solution of colloidal bead-milled up-converting phosphor nanoparticles provides intense green emission visible to the human eye under illumination by an infrared laser pointer. In this article, we show that the unique photoluminescence properties of the up-converting phosphors and the inexpensive measurement configuration, which is adequate for their sensitive detection, render the up-conversion an attractive alternative to the ultraviolet-excited time-resolved fluorescence of down-converting lanthanide compounds widely employed in biomedical research and diagnostics.     

Photoluminescence of CdS nanoparticles embedded in a starch matrix

CdS nanoparticles were synthesized by precipitation in aqueous solution using starch as the capping molecule, and the effect of the pH of the solution on the optical absorption, photoluminescence, and size of the nanoparticles was studied. Absorption spectra, obtained by photoacoustic spectroscopy, indicated that the band gap energy of the crystalline nanoparticles decreased from 2.68 eV down to 2.48 eV by increasing the pH of the solution from 9 up to 14. The X-ray diffraction analysis revealed that the CdS nanoparticles were of zinc blende structure, and that the particle size increased from 1.35 nm up to 2.45 nm with increasing pH. In addition, temperature-dependent photoluminescence (PL) measurements of the capped material showed a blue-shift of the emission peak for temperatures higher than 150 K, indicating the influence of starch on the formation of defect levels on the surface of the CdS nanoparticles.     

飞秒脉冲激光辐照下硅表面光致荧光特性(英文)

采用钛宝石飞秒脉冲激光对单晶硅在空气中进行辐照,研究了硅表面在不同扫描速度和能量密度下的光致荧光特性。光致荧光谱(PL)测量表明,在样品没有退火处理的情况下,激光扫描区域观察到橙色荧光峰(603nm)和红色荧光带(680nm附近)。扫描电子显微镜(SEM)测量显示,在飞秒脉冲激光辐照硅样品的过程中硅表面沉积了大量的纳米颗粒。利用傅里叶变换红外光谱仪(FT-IR)检测到了低值氧化物SiOx(x2)的存在,并且结合能谱仪(EDS)检测结果发现氧元素在光致发光中起着重要作用。研究表明:603nm处橙色荧光峰来自微构造硅表面低值氧化物SiOx,680nm附近红色荧光带来自量子限制效应。同时样品表面硅纳米颗粒的尺寸和氧元素的浓度分别决定了红色荧光带和橙色荧光的强度,通过调节飞秒激光脉冲的扫描速度和能量密度,可以有效地控制样品的荧光强度。     

Photoluminescence study on amino functionalized dysprosium oxide–zinc oxide composite bifunctional nanoparticles

An organic dispersion of 9–15 nm size stable dysprosium oxide incorporated zinc oxide nanocomposites exhibiting luminescence in the visible region has been synthesised by a wet chemical precipitation technique at room temperature. Tetraethoxysilane TEOS [(C₂H₅O)₄Si], (3-aminopropyl) trimethoxysilane (APTS) and a 1:1 mixture of TEOS–APTS have been used as capping agents to control the particle size as well as to achieve uniform dispersion of composite nanoparticles in methanol medium. X-ray diffractometer (XRD) analysis reveals the formation phase of amino-functionalised colloidal dysprosium oxide incorporated ZnO composite nanoparticles to be of zincite structure. The Transmission Electron Microscopy (TEM) images show that the particles are spheroids in shape, having average crystalline sizes ranging from 9 to 15 nm. The photoluminescence (PL) observed in these composites has been attributed to the presence of near band edge excitonic emission and existence of defect centres. The time correlated single photon counting studies of the composite nanoparticles exhibited three decay pathways. The enhanced PL emission intensity of solid state fluorescence spectra of samples is attributed to the absence of vibrational relaxation process.     

Size effects on the magnetic and optical properties of CuO nanoparticles

Optical and magnetic studies on CuO nanoparticles prepared by a chemical route are reported and the effect of size variation on these properties is discussed. SEM images show that the nanoparticles are interlinked into microspheres with the cages containing visible nanoscale holes. Diffuse reflectance spectroscopy indicates a consistent red shift in the fundamental band gap (indirect band gap) from 1.23 to 1 eV as the size decreases from 29 to 11 nm. This observed red shift is attributed to the presence of defect states within the band gap. A clear blue shift is observed in the direct band gap of these nanoparticles presumably due to the quantum confinement effects. Air-annealed samples show a paramagnetic response whereas particles annealed in a reducing atmosphere show additionally a weak ferromagnetic component at room temperature. For both types of particles, the paramagnetic and ferromagnetic moments, respectively, increase with decreasing size. The role of oxygen vacancies is understood to relate to the generation of free carriers mediating ferromagnetism between Cu spins. AC susceptibility measurements show both the antiferromagnetic transitions of CuO including the one at 231 K which is associated with the onset of the spiral antiferromagnetic phase transition.     

ZnO/CuO 核壳结构纳米线光致发光性能 与CuO壳层厚度的关系

通过分别生长核层与壳层制备出了ZnO/CuO核壳结构的纳米线。形貌和结构分析表明,ZnO核为单晶纳米线而CuO则以多晶形式覆盖在核层表面上。光致发光(PL)研究表明,ZnO纳米线PL强度随CuO壳层厚度的变化而变化。当壳层比较薄时ZnO的PL强度增大,这主要是由于CuO壳层对ZnO核层的修饰减少了表面态,而当壳层厚度增加到一定程度时,ZnO的PL强度不再变化,这主要是由于在核壳结构中形成了type-I型结构的原因。我们对这一现象做了详细的讨论。     

Effect of sol–gel pH on XRD peak broadening,lattice strain,ferroelectric domain orientation,and optical bandgap of nanocrystalline Pb1.1(Zr0.52Ti0.48)O3

Nanocrystalline Pb_1.1(Zr_0.52Ti_0.48)O₃ (PZT) samples were prepared using a citrate–nitrate sol–gel process near the morphotropic phase boundary. The effect of pH on the lattice parameters (tetragonality and lattice constants), crystal structure [strain broadening, relative phase content, ferroelectric domain (FD) orientation and nanocrystallite size], microstructure (grain size and particle morphology) and optical bandgap was investigated. The samples were characterized using X-ray diffraction (XRD), the size strain plot (SSP) method, Fourier-transform infrared spectroscopy, and the classical Tauc relation. The particle morphology was investigated using field-emission scanning electron microscopy. The XRD results revealed a perovskite structure and coexisting tetragonal and rhombohedral phases for all PZT samples. Lattice strain and peak broadening were determined from SSP and XRD results. The behavior of these parameters was in agreement for all pH values. The optical bandgap for PZT was estimated from UV-vis absorption spectra. We found that for PZT the maximum relative tetragonal phase content, c/a ratio, and FD orientation along the a-axis occurred at pH 4.     

MOVPE 生长GaN薄膜的 光致黄带发光与激发光源的相关性

用四种不同光源作为激发光源,研究了蓝宝石衬底金属有机物汽相外延方法生长的氮化镓薄膜的光致发光特性。结果发现用连续光作为激发光源时,光致发光谱中除出现365 nm的带边发射峰外,同时观察到中心波长位于约550 nm 的较宽黄带发光;而用脉冲光作为激发光源时其发光光谱主要是365 nm附近的带边发光峰,未观察到黄带发光。氮化镓薄膜的光致发光特性依赖于所用的激发光源性质。