水溶性CdTe/CdS纳米晶表面SiO2壳层的反相胶束法包覆

"提出了一种水相中制备CdTe/CdS核壳结构纳米粒子的方法.用Te粉作为碲源,用Na2S作为硫源,在50 ℃下制备了CdTe/CdS核壳结构纳米粒子. 用紫外可见吸收光谱和荧光光谱分析了CdS壳层对CdTe核的影响. 随CdS壳层厚度的增加,紫外可见吸收光谱和荧光光谱均发生了红移. CdS壳层厚度较薄时,CdTe/CdS纳米晶的荧光强度较CdTe纳米粒子有显著提高;而CdS壳层厚度较厚时,CdTe/CdS纳米晶的荧光强度会逐渐降低. 用反相胶束法在CdTe/CdS核壳结构纳米粒子的表面包被一层SiO2,     

Large Third-Order Optical Nonlinearity of Cadmium Sulphide Nanoparticles Embedded in Polymer Thin Films

A simple method for synthesis of well dispersed cadmium sulphide nanoparticles embedded in a polyethylene glycol matrix （PEG 400） in thin film form is presented. The large blue shift of the band gap energy of the CdS nanoparticles compared to the bulk semiconductors is observed via UV-vis absorption spectra. Photoluminescence spectra of CdS nanocomposite films show that the emission peaks shift towards the longer wavelength with the increase of annealing temperature. Transmission electron microscopic images as well as Raman scattering studies confirm the CdS nanometer size particle formation within the polymer matrix. The particle size is about 8 nm. Selected area electron diffraction （SAED） shows the cubic zinc blende polycrystalline rings. Third-order optical nonlinearity of the CdS nanopartieles embedded in polymer thin films is studied with the Z-scan technique under 1064 nm excitation. The results show that the CdS nanocomposite film exhibits negative nonlinear refraction index and positive absorption coefficient. The film shows large optical nonlinearity, and the magnitude of the third-order nonlinear susceptibility of the film is calculated to be 1.73 × 10^-9 esu. The corresponding mechanism is discussed.     

Synthesis of nanocrystalline CdS thin film by SILAR and their characterization

Cadmium sulphide (CdS) thin film was prepared by successive ion layer adsorption and reaction (SILAR) technique using ammonium sulphide as anionic precursor. Characterization techniques of XRD, SEM, TEM, FTIR and EDX were utilized to study the microstructure of the films. Structural characterization by x-ray diffraction reveals the polycrystalline nature of the films. Cubic structure is revealed from X-ray diffraction and selected area diffraction (SAD) patterns. The particle size estimated using X-ray line broadening method is approximately 7 nm. Instrumental broadening was taken into account while particle size estimation. TEM shows CdS nanoparticles in the range 5–15 nm. Elemental mapping using EFTEM reveals good stoichiometric composition of CdS. Characteristic stretching vibration mode of CdS was observed in the absorption band of FTIR spectrum. Optical absorption study exhibits a distinct blue shift in band gap energy value of about 2.56 eV which confirms the size quantization.     

核壳结构CdS/ZnS纳米微粒的制备与光学特性

用微乳液法制备CdS纳米微粒 ,以ZnS对其进行表面修饰 ,得到具有核壳结构的CdS/ZnS纳米微粒 .采用X射线衍射 (XRD)、透射电镜 (TEM )表征其结构、粒度和形貌 ,紫外 可见吸收光谱 (UV)、光致发光光谱(PL)表征其光学特性 .制得的CdS近似呈球形 ,直径为 3.3nm ;以XRD和UV证实了CdS/ZnS核壳结构的实现 .研究了不同ZnS壳层厚度对CdS纳米微粒光学性能的影响 ,UV谱表明随着壳层厚度的增加纳米微粒的吸收带边有轻微的红移 ,同时短波吸收增强 ;PL谱表明壳层ZnS的包覆可减少CdS纳米微粒的表面缺陷 ,带边直接复合发光的几率增大 ,具有合适的壳层厚度时发光效率大大提高 .     

Photoluminescence and optical characterization of CdS nanoparticles prepared by solid-state method at low temperature

The photoluminescence (PL) and optical properties of CdS nanoparticles prepared by the solid-state method at low temperature have been discussed. The effects of NaCl and anionic surfactant SDBS (sodium dodecylbenzene sulfonate) on the luminescent properties of CdS nanophosphors prepared using this method, without the inert gas or the H₂S environment, were studied separately. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectroscopy (EDAX). UV–VIS absorption and PL spectra were also studied. XRD studies confirmed the single-phase formation of CdS nanoparticles. TEM micrograph revealed the formation of nearly spherical nanoparticles with a diameter of 2.5 nm. The PL emission for the CdS shows the main peak at 560 nm with a shoulder at 624 nm, with an increase in the PL intensity after the addition of SDBS. The effect of Mn doping on PL intensity has also been investigated. The PL spectra show that the emission intensity decreases as the dopant concentration increases.     

Sono-synthesis of core-shell nanocrystal (CdS/TiO2) without surfactant

A core-shell nanocomposite (CdS/TiO(2)) was synthesized at relatively low temperature (70°C) with small particle sizes (~11 nm). First, CdS nanoparticles were prepared by a combination of ultrasound and new micro-emulsion (O/W) without surfactant. Then the synthesized CdS was easily combined with TiO(2) under sonication. The formation of uniform surface layer of TiO(2) with depths of 0.75-1.1 nm on the CdS led to an increase of particle size. Ultrasonic irradiation can control the hydrolysis and condensation of titanium tetra-isopropoxide (TTIP) and the formation of TiO(2) shell around the CdS core. This technique avoids some of the problems that exist in conventional microemulsion synthesis such as the presence of different additives and calcinations. It was found that nanocomposite particles extend the optical absorption spectrum into the visible region in comparison with pure TiO(2) and pure CdS. In addition, a larger depth of TiO(2) led to a red-shift of the absorption band in nanocomposite. The characterization of nanocomposites has been studied by HRTEM, TEM, XRD, EDAX, BET and, UV-vis.     

Synthesis, surface morphology, and optical and structural properties of CdS and ZnS nanoparticles

Synthesis of CdS and ZnS nanoparticles in reverse micelles and organic solvents has been carried out. Particles with a hexagonal structure 2–5 nm in size are formed during synthesis. Maintaining the reaction mixture at room temperature leads to the formation of nanoparticles with a cubic structure 100–150 nm in size. The changes in the optical properties of CdS and ZnS nanoparticles, depending on the synthesis method and conditions and on the precursors used, have been investigated. The luminescence characteristics of local surface defects of nanoparticles depend weakly on nanoparticle sizes. The dependence of the fluorescence and phosphorescence intensity of nanoparticle surface defects on the polarity of surrounding solution is demonstrated; thus, these particles can be used as polarity indicators.     

Influence of two different template removal methods on the micromorphology,crystal structure,and photocatalytic activity of hollow CdS nanospheres

Hollow cadmium sulfide (CdS) nanospheres of about 260 nm average diameters and about 30 nm shell thickness can be easily synthesized via a sonochemical process, in which polystyrene (PS) nanoparticles were employed as templates. In order to remove the PS templates, both etching and calcination were applied in this paper. The influence of the two different template removal methods on the surface micromorphology, crystal structure, and photocatalytic activity of hollow CdS nanospheres was carefully performed a comparative study. Results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray, FT-IR, thermogravimetric analysis, Brunauer–Emmett–Teller, diffused reflectance spectra, and decolorization experiments showed that the different template removal methods exhibited a significant influence on the surface micromorphology, crystal structure, and photocatalytic activity of hollow CdS nanospheres. The CdS hollow nanospheres as-prepared by etching had pure cubic sphalerite structure, higher –OH content, less defects and exhibited good photocatalytic activity for rhodamine-B, Methylene Blue and methyl orange under UV–vis light irradiation. However, CdS hollow nanospheres obtained by calcination with a hexagonal crystal structure, less –OH content, more defects have shown worse photocatalytic activity. This indicated that surface micromorphology and crystalline phase were mainly factors influencing photocatalytic activity of hollow CdS nanospheres.     

Optical and AFM study of electrostatically assembled films of CdS and ZnS colloid nanoparticles

CdS and ZnS semiconducting colloid nanoparticles coated with the organic shell, containing either SO₃⁻ or NH₂⁺ groups, were prepared using the aqueous phase synthesis. The multilayer films of CdS (or ZnS) were deposited onto glass, quartz and silicon substrates using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy, spectroscopic ellipsometry and atomic force microscopy. A substantial blue shift of the main absorption band with respect to the bulk materials was found for both CdS and ZnS films. The Efros equation in the effective mass approximation (EMA) theoretical model allowed the evaluation of the nanoparticle radius of 1.8 nm, which corresponds well to the ellipsometry results. AFM shows the formation of larger aggregates of nanoparticles on solid surfaces.     

Synthesis and characterization of CdS/PVA nanocomposite films

A series CdS/PVA nanocomposite films with different amount of Cd salt have been prepared by means of the in situ synthesis method via the reaction of Cd²⁺-dispersed poly vinyl-alcohol (PVA) with H₂S. The as-prepared films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption, photoluminescence (PL) spectra, Fourier transform infrared spectroscope (FTIR) and thermogravimetric analysis (TGA). The XRD results indicated the formation of CdS nanoparticles with hexagonal phase in the PVA matrix. The primary FTIR spectra of CdS/PVA nanocomposite in different processing stages have been discussed. The vibrational absorption peak of CdS bond at 405 cm⁻¹ was observed, which further testified the generation of CdS nanoparticles. The TGA results showed incorporation of CdS nanoparticles significantly altered the thermal properties of PVA matrix. The photoluminescence and UV-vis spectroscopy revealed that the CdS/PVA films showed quantum confinement effect.     

A mathematical model to predict the grain size of nanocrystalline CdS thin films based on the deposition condition used in the sol–gel spin coating method

Design of experiment (DOE) based on central composite design (CCD) has been employed for the development of a mathematical model correlating the important process parameters like thiourea concentration (U), annealing temperature (A), rotational speed (S), and annealing time (T) of the spin coating process for the preparation of CdS thin films. The experiments were conducted as per the design matrix. Nanocrystalline CdS thin films have been prepared using cadmium nitrate and thiourea as precursors by sol gel spin coating method using the results of the mathematical model. The prepared CdS films have been characterized and the crystal structure and grain size of the samples were analyzed using X-ray diffraction technique. The adequacy of the developed models was checked by analysis of variance (ANOVA) technique. The accuracy of prediction has been carried out by conducting confirmation test. Using this model, the main effect of process parameters on grain size of CdS films have been studied. These parameters were optimized to obtain minimum grain size using the Microsoft excel solver. The results have been verified by depositing CdS films using the optimized conditions. These films have been characterized using X-ray diffraction technique and the grain size is found to be 8.8 nm. The high resolution transmission electron microscopy (HRTEM) analysis showed the grain size of the prepared CdS film to be ∼7 nm. UV–vis spectroscopy analysis revealed that CdS films exhibited quantum confinement effect.     

化学水浴法和磁控溅射法制备硫化镉薄膜的性能研究

以氯化铵、氯化镉、氢氧化钾和硫脲为反应物采用化学水浴法制备了硫化镉薄膜,为了作对比研究,采用射频磁控溅射以硫化镉为靶材,氩气为溅射气体,制备了硫化镉薄膜。采用X射线衍射、扫描电子显微镜和紫外-可见光光谱仪分别表征了硫化镉薄膜的结构、形貌和光学吸收特性。结果表明,采用以上两种方法制备的硫化镉均具有(002)择优取向,溅射法制备的硫化镉薄膜较致密,薄膜表面较光滑,平均晶粒尺寸在20～30nm;水浴法制备的硫化镉薄膜颗粒尺寸较小,缺陷较多。除了在短波段溅射所得硫化镉薄膜的透过率略差于水浴法所得硫化镉薄膜之外,溅射法制备的硫化镉薄膜的性能整体上优于水浴法制备的薄膜。两种方法制备的硫化镉薄膜的能隙在2.3～2.5eV。     

Polymeric nano-micelles as drug carrier using polyethylene glycol and polytrimethylene carbonate linear and star-shaped block copolymer

The polymerization of trimethylene carbonate (TMC) in the presence of HCl · Et₂O via activated monomer mechanism was performed to synthesize linear and star-shaped block copolymers composed of polyethyleneglycol (PEG) and poly(trimethylene carbonate) (PTMC). The obtained PTMCs had molecular weights close to the theoretical values calculated from the TMC to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PTMC linear and star-shaped block copolymers by activated monomer mechanism. The characterization for formation of micelle of block copolymers in an aqueous phase was carried out by using NMR, dynamic light scattering (DLS), AFM and fluorescence techniques (FL). The block copolymers gave micelles with a critical micelle concentration (CMC) ranging 1.88 × 10⁻²–3.09 × 10⁻³ mg/mL depended on the molecular shape of block copolymers. The diameters of micelles, measured by DLS, were 100–250 nm. Most micelles exhibited a spherical shape in AFM.     

Tuning of optical properties of CdS nanoparticles synthesized in a glass matrix

Attempts were made to provide the data concerning directed synthesis of semiconductor nanoparticles in a dielectric silica-based glass matrix. These attempts involve finding out the connections between the structure, size of CdS nanoparticles, and optical properties of the nanocomposites produced. High-resolution focused ion beam scanning electron microscopy images of CdS nanoparticles incorporated in glass and SAXS results confirm the formation of uniformly distributed spherical CdS nanoparticles with an average diameter of about 6.2 nm. UV–Vis measurements show that CdS composites possess a direct bandgap wider than 2.45 eV depending on the heat treatment conditions; thus, heat treatment can be used to control nanoparticle size in each selected composite. The emission spectra showed a maximum at about 603 nm and a red shift of about 100 nm with increasing annealing temperature that is associated with the presence of defect states in the nanoparticles. In addition, semiconductor phase concentration in the glass matrix was found by using optical absorption data for the first time, which allows understanding the effect of nanocomposite structure on luminescence properties.     

Study of nano-CdS prepared in methanolic solution and polymer electrolyte matrix

This present paper reports the study of cadmium sulphide (CdS) nanoparticles prepared under controlled condition in methanolic solution and also in polyethylene oxide polymer electrolyte matrix. The sulphurations of the cadmium salts were done in situ by a sodium sulphide solution. The concentration of the precursors has been controlled as detailed in the paper. All the preparation and characterization were carried out at room temperature. The nanoparticles were characterized by UV/Vis spectra in the range of 600 to 250 nm. The absence of bulk/micron size particles was noted in either of the system. The absorption edge near 510 nm indicates the presence of bulk CdS, whereas the presence of nanometer-sized particles is also reflected in low wavelength region. The sizes of the particles as well as particle distribution have been estimated using X-ray diffraction and scanning electron microscopy, respectively. A comparison in the spectra has been done for the sample prepared in either of the matrices. The particle size distribution in the polymeric matrix has been found to be more in comparison to that in the methanolic suspension. The polymer is reported to work as a binder, but not as a capping agent.     

CdS/ZnS core–shell nanoparticles in arachidic acid LB films

Core–shell CdS/ZnS nanoparticles in arachidic acid film were prepared through a novel Langmuir–Blodgett (LB) approach. Post-deposition treatment of the precursor LB multilayers of cadmium arachidate with H₂S gas followed by intercalation of Zn²⁺ ions and further sulfidation result in the formation of CdS/ZnS nanoparticles in the LB film. The formation of these nanoparticles and resulting changes in layered structures were studied by FTIR and X-ray reflection measurements. The optical properties were studied using UV–vis absorption and photoluminescence spectroscopy. A red-shift in the absorption spectrum and enhancement of CdS excitonic emission together with reduction of surface states emission suggest that after the intercalation step, a thin layer of ZnS surrounds the CdS nanoparticles, thus forming a core–shell structure. Subsequent to the second sulfidation, a further red-shift in absorption suggests the formation of a thicker ZnS coating on CdS. Electron diffraction of CdS nanoparticles coated with thicker ZnS showed the diffraction patterns of only ZnS, as expected for core–shell structures.     

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.     

Synthesis and characterization of Cr doped CdS nanoparticles stabilized with polyvinylpyrrolidone

Undoped and Cr (2 and 4 at.%) doped CdS nanoparticles were synthesized in aqueous solution by simple chemical co-precipitation method using polyvinylpyrrolidone (PVP) as stabilizer. The prepared nanoparticles were examined using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). XRD pattern of the nanoparticles showed cubic zincblende phase with the particle size of the order of 3-4 nm, which was in good agreement with the results obtained from TEM studies. The EDAX analysis confirmed that Cd, Cr and S elements were present in the samples and the variations between the target and actual compositions were microscopic. UV-vis DRS spectra of the samples exhibited decrease in the band gap which further attests the incorporation of Cr into CdS nanoparticles. FTIR studies revealed that the undoped as well as Cr doped CdS nanoparticles were capped by polyvinylpyrrolidone.     

Linear assemblies of aged CdS particles and cationic porphyrin in multilayer films

Multilayer films of CdS particles and meso-tetra-(4-trimethylaminophenyl)porphyrin cobalt iodide (CoTAPPI) were fabricated via layer-by-layer self-assembly technique. UV-vis absorption spectra, fluorescence spectra and SEM images were used to compare the differences between the films prepared from freshly synthesized nanoparticles and from aged particles. SEM images show the aged CdS particles and CoTAPPI in the multilayer film, assembling in a linear structure. The mechanism of dipole-dipole interaction was presented to explain linear formation.     

Synthesis and optical characterization of monodispersed Mn doped CdS nanoparticles

Monodispersed Mn²⁺ doped CdS nanoparticles with average size as small as 1.8 nm have been synthesized through chemical method. The nanostructures of the prepared nanoparticles have been confirmed through X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption and transmission electron microscope (TEM) measurements. The photoluminescence emission covering 450-650 nm of the visible region is observed under ultraviolet light excitation, from Mn²⁺ doped CdS nanoparticles dispersed in dimethyl sulfoxide (DMSO).