Synthesis and characterization of CdS nanoparticles in the presence of oleic acid as solvent and stabilizer

Oleic acid (OA)-capped CdS nanoparticles (NPs) have been successfully synthesized via the direct reaction of Cd(CH₂COO)₂·2H₂O with S powder in OA solvent at 230 °C under nitrogen flow, which was a kind of clean and air-stable solvent. The morphologies and structures of the as-synthesized CdS NPs are examined by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), and Fourier transform infrared (FTIR) spectroscopy, and the typical Ostwald ripening growth mechanism is concluded. Moreover, the collected ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) spectroscopy demonstrate good optical properties of CdS NPs.     

Effect of CdS nanoparticles on fluorescence from Sm doped SiO2 glass

Sm³⁺ doped CdS nanoparticles have been prepared by sol-gel method. The effect of annealing temperatures and doping concentrations of CdS on the photoluminescence spectra of Sm³⁺ were studied. From the measurement of its optical absorption, three phenomenological Judd-Ofelt intensity parameters (Ω₂, Ω₄, and Ω₆) have been computed and used to parameterize the radiative properties. The influences of CdS on Sm³⁺ ions were studied by fluorescence spectroscopy. The fluorescence spectra revealed that the emission intensity of samarium increased considerably in the presence of CdS nanoparticles. The evaluation of radiative properties of Sm³⁺ containing CdS showed that the ⁴G_5/2→⁶H_7/2 transition in silica matrix had the potential to be a laser transition.     

Surface and interface optical phonon modes and electron-phonon interaction in a multi-shell spherical system

Within the framework of the dielectric continuum model, interface optical(IO) and surface optical(SO) phonon modes and the Fr?hlich electron-IO (SO) phonon interaction Hamiltonian in a multi-shell spherical system were derived and studied. Numerical calculation on CdS/HgS/H₂O and CdS/HgS/CdS/H₂O spherical systems have been performed. Results reveal that there are two IO modes and one SO mode for the CdS/HgS/H₂O system, one SO mode and four IO modes whose frequencies approach the IO phonon frequencies of the single CdS/HgS heterostructure with the increasing of the quantum number l for CdS/HgS/CdS/H₂O. It also showed that smaller l and SO phonon compared with IO phonon, have more significant contribution to the electron-IO (SO) phonon interaction. Received 16 October 2001 and Received in final form 23 January 2002 Published online 25 June 2002     

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.     

Enhanced Oxidation Stability of Quasi Core-Shell Alloyed CdSeS Quantum Dots Prepared Through Aqueous Microwave Synthesis Technique

Quasi core shell alloyed CdSeS quantum dots (QDs) have been prepared through a facile aqueous-phase route employing microwave irradiation technique. The optical spectroscopy and structure characterization evidenced the quasi core shell alloyed structures of CdSeS QDs. The X-ray diffraction patterns of the obtained CdSeS QDs displayed peak positions very close to those of bulk cubic CdS crystal structures and the result of X-ray photoelectron spectroscopy data re-confirmed the thick CdS shell on the CdSe core. The TEM images and HRTEM images of the CdSeS QDs ascertained the well-defined spherical particles and a relatively narrow size distribution. On the basis, the stability of the obtained QDs in an oxidative environment was also discussed using etching reaction by H₂O₂. The experiments result showed the as-prepared QDs present high tolerance towards H₂O₂, obviously superior to the commonly used CdTe QDs and core-shell CdTe/CdS QDs, which was attributed to the unique quasi core-shell CdSeS crystal structure and the small lattice mismatch between CdSe and CdS semiconductor materials. This assay provided insight to obtain high stable crystal structured semiconductor nanocrystals in the design and synthesis process.     

Fluorescence quenching of 3,7-diamino-2,8-dimethyl-5-phenyl phenazinium chloride by AgCl and Ag nanoparticles

Quenching of fluorescence of the dye 3,7-diamino-2,8-dimethyl-5-phenyl Phenazinium Chloride (Safranine T) has been investigated by AgCl nanoparticles in the W/O microemulsion medium at different [H₂O]/[AOT] ratios (ω) and with Ag nanoparticles and Ag⁺ in aqueous medium. A simple straightforward method has been introduced to prepare AgCl nanoparticles in well-characterized, monodispersed biomimicking nanocavities formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane. Experimental results reveal that the size of the AgCl nanoparticles increases with increase in hydration. The results of the quenching experiment were analysed in the light of Stern Volmer equation. Quenching of fluorescence of the dye has been found to decrease with decrease in the size of the nanoparticles of AgCl and the variation of Stern Volmer quenching constants (K_SV) with particle size is different for two different size regimes.     

Effect of pyridine as a ligand in precursor on morphology of CdS nanoparticles

[Cd(thqdtc)₂], [Cd(thqdtc)₂(py)] and [Cd(thqdtc)₂(2,2′-bipy)] (where thqdtc = 1,2,3,4-tetrahydroquinolinecarbodithioate; py = pyridine; 2,2′-bipy = 2,2′-bipyridine) have been found to be effective single source precursors for the preparation of diethylenetriamine capped CdS nanoparticles via solvothermal method. Flower-like and rod-like CdS nanoparticles were prepared at a relatively low temperature by thermolysis of the precursors using chelating solvent diethylenetriamine. Use of [Cd(thqdtc)₂] and [Cd(thqdtc)₂(2,2′-bipy)] afforded rod-shaped nanoparticles and flower-like nanoparticles obtained from [Cd(thqdtc)₂(py)]. UV–Visible spectroscopy established pronounced quantum confinement effect. X-ray diffraction (XRD) analysis revealed hexagonal crystal phase for so obtained CdS nanoparticles. The nanoparticles were also characterized by transmission electron microscopy (TEM) and fluorescence spectroscopy.     

Nonlinear optical characteristics of CdS and ZnS nanoparticles implanted into zirconium oxide thin films

The nonlinear refractive indices γ and nonlinear absorption coefficients of ZrO₂ films doped with CdS or ZnS nanoparticles, as well as with various metals, are measured. The effects of semiconductor and metal nanoparticles and annealing on the nonlinear optical properties of films are studied. The structural parameters of films, determined by electron microscopy and x-ray dispersion spectroscopy, are compared to the optical and nonlinear optical characteristics of these media. The high magnitude of γ of the films ((3±0.6)×10^?11 cm² W^{? 1}) is attributed to the surface enhancement effect in semiconductor nanoparticles. On the basis of Z-scan data obtained at different intensities of radiation, it is shown that the variations in γ of the ZrO₂:CdS(Cr) and ZrO₂:ZnS(Mn) films are related to the generation of free carriers.     

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。     

表面修饰的CdS纳米荧光探针的研究

采用溶胶-凝胶法合成硫脲表面修饰的硫化镉纳米粒子[CdS/SC(NH₂)₂],研究硫脲的用量对其粒径的影响,用X射线粉末衍射、透射电子显微镜,红外光谱以及荧光光谱等手段进行了表征。并研究了小牛胸腺DNA的加入对该纳米粒子荧光光谱的影响。实验结果表明,硫脲的用量对该纳米粒子的粒径大小及发光特性有明显影响,随反应物中硫脲与镉离子的物质的量的比值增加,CdS/SC(NH₂)₂纳米粒子粒径变小,其发射波长蓝移,表现出明显的量子尺寸特性;小牛胸腺DNA的加入使CdS/SC(NH₂)₂纳米粒子的发射光谱强度减弱,实验推测该纳米粒子与小牛胸腺DNA存在静电相互作用, 该研究结果可望用于DNA的分析测定。     

Synthesis and characterization of Rh(PVP) nanoparticles studied by XPS and NEXAFS

Rhodium nanoparticles were synthesized by the reduction of Rh³⁺ ion in ethanol solvent with use of the polyvinylpyrrolidone (PVP) of various molecular weights and the solvent of different volume ratios of water to ethanol. The formed Rh(PVP) nanoparticles have been characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) techniques. The TEM and AFM results show that the Rh(PVP) nanoparticles are monodispersed and do not agglomerate with each other. The particle size can be controlled by the molecular weight of PVP and/or the water/ethanol ratio of the solvent. The XPS and NEXAFS results indicate that the chlorine derived from RhCl₃(3H₂O) remains in the obtained nanoparticles but can be removed by heating.     

Optical properties of cadmium sulfide nanocrystal film prepared by electrochemical synthesis at liquid-liquid interface

Dendritic nanocrystalline CdS film was deposited at liquid-liquid interface of surfactants and an electrolyte containing 4 mmol L⁻¹ cadmium chloride (CdCl₂) and 16 mmol L⁻¹ thioacetamide (CH₃CSNH₂) with an initial pH value of 5 at 15 °C by electrochemical synthesis. The nanofilm was characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), ultraviolet visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy. The surface morphology and particle size of the nanofilm were investigated by AFM, SEM and TEM, and the crystalline size was 30-50 nm. The thickness of the nanofilm calculated by optical absorption spectrum was 80 nm. The microstructure and composition of the nanofilm was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), showing its polycrystalline structure consisting of CdS and Cd. Optical properties of the nanofilm were investigated systematically by UV-vis absorption and fluorescence spectroscopy. A λ_onset blue shift compared with bulk CdS was observed in the absorption spectra. Fluorescence spectra of the nanofilm indicated that the CdS nanofilm emitted blue and green light. The nanocomposites film electrode will bring about anodic photocurrent during illumination, showing that the transfer of cavities produces photocurrent.     

Synthesis and Characterization of CdS/CISe Quantum Dots with Core–Shell Structure

Quantum dots have received great interest due to their excellent optoelectronic properties. However, the surface defects of quantum dots affect the carrier transport and ultimately reduce the photovoltaic efficiency. In this paper, a core–shell quantum dot by hot-injection method is prepared to grow a narrow-band semiconductor layer (CuInSe₂ (CISe) quantumdot) on the surface of a broad-band core material (cadmium sulfide (CdS) nanocrystal). The composition, structure, optical properties, and decay lifetime of CdS/CISe core–shells are investigated in more detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), UV–vis spectrophotometry, and fluorescence spectroscopy. The CdS/CISe core–shell structure has a broadened absorption range and still shows CISe-related quantum effects. The increased size of the core–shell and the smaller specific surface area of the CISe shell layer lead to a lower carrier complexation chance, which improves the carrier lifetime.     

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.     

Aggregate structure and crystallite size of platinum nanoparticles synthesized by ethanol reduction

Monodispersed platinum (Pt) nanoparticles were synthesized from reducing hydrated hydrogen hexachloroplatinic acid (H₂PtCl₆·nH₂O) with ethanol in the presence of polyvinylpyrrolidone (PVP) as a steric stabilizer. Concentration of both PVP and ethanol influenced the aggregate structure and crystallite size of the nanoparticles. When the molar ratio of monomeric unit of PVP to Pt, i.e., [PVP]/[Pt], was one, the synthesized Pt particles coagulated pronouncedly into an inter-connected particulate network or self-organized into spherical superstructures with an apparent diameter ranging from 60 to 80 nm, depending on the ethanol concentration. The geometry and structure of these complex aggregates were characterized by fractal analysis. Fractal dimensions of 2.13–2.23 in three dimensions were determined from the Richardson’s plot, which suggests that a reaction-limited cluster–cluster aggregation model (RCLA) was operative. The Pt colloids became apparently more stable when the [PVP]/[Pt] ratio was increased greater than 20. Crystallite size of the Pt nanoparticles was found to increase linearly with the ethanol concentration as the [PVP]/[Pt] was held at one. This suggests that the reduction rate of PtCl₆ ²⁻ ions in solution is critically important to the synthesized crystallite size.     

Optical Properties of CdS–PVA Nanocomposites

Semiconductor–polymer nanocomposites, with good control over the nanoparticle size and their dispersion within the polymer matrix, can have applications in many optical and luminescent display devices. Cadmium sulphide (CdS) is the most popular semiconductor nanoparticle exhibiting size dependent properties due to its large exciton binding energy and its suitability for large scale production. The nanoparticles need to be passivated against aggregation with suitable capping agents, without sacrificing the desirable properties like transparency and flexibility of the polymer. Cadmium sulphide nanoparticles capped with polyvinyl pyrrolidone (PVP) are synthesized using cadmium nitrate (Cd(NO₃)₂) and hydrogen sulphide (H₂S) as Cd²⁺ and S^2– sources, respectively. CdS particles with sizes in the range of 5–6 nm are prepared in methanol and the solvent is removed using a rotary evaporator. CdS powder is dispersed in polyvinyl alcohol (PVA) solution with dimethyl formamide (DMF) as solvent to get (PVP–CdS)–PVA nanocomposite film of about 0.2 mm thickness. This has been characterized by powder X-ray diffraction (XRD), optical absorption studies, transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and photoluminescence (PL). Particle size does not change due to incorporation in the polymer matrix and the polymer retains its transparency and flexibility. The nanocomposite shows good photoluminescence property with stronger band edge emission than defect related emission. The latter could be quenched completely by optimizing the PVP content. Irradiation of the nanocomposite with 8 MeV electrons at a dose of 100 kGy could effectively quench the defect related emission.     

TMOS based water repellent silica thin films by co-precursor method using TMES as a hydrophobic agent

The present paper describes the room temperature synthesis of dip coated water repellent silica coatings on glass substrates using trimethylethoxysilane (TMES) as a co-precursor. Silica sol was prepared by keeping the molar ratio of tetramethoxysilane (TMOS) precursor, methanol (MeOH) solvent, water (H₂O) constant at 1:29.27:2.09 respectively, with 0.5 M NH₄OH throughout the experiments and the TMES/TMOS molar ratio (M) was varied from 0 to 3.8. It was found that with an increase in M value, the roughness and hydrophobicity of the films increased, however the optical transmission decreased from 93% to 57% in the visible range. The hydrophobic silica films retained their hydrophobicity up to a temperature of 250 °C and above this temperature the films became hydrophilic. The hydrophobic silica thin films were characterized by taking into consideration the surface roughness studies, Fourier transform infrared (FT-IR) spectroscopy, percentage of optical transmission, scanning electron microscopy (SEM) and contact angle measurements.     

Characterization of CBD-CdSe1-ySy deposited at low-temperature for photovoltaic applications

We present the structural and optical characterization of cadmium selenide sulphur (CdSe_1-yS_y) deposited by chemical bath deposition (CBD) technique at low-temperature (20 ± 2 °C). The sulphur molar fraction is varied from 0 to 42.13%. The chemical stoichiometry is estimated by energy-dispersive X-ray spectroscopy (EDS). The CdSe_1-yS_y shows hexagonal wurtzite crystalline phase, which was found by X-ray diffraction (XRD) analysis and it was confirmed by Raman spectroscopy. The average grain size of the CdSe_1-yS_y films was ranged from 1.20 to 1.68 nm that was determined by Debye-Scherrer equation from W(002) direction and it was confirmed by high resolution transmission electron microscopy (HRTEM). This average grain size indicates a high quantum confinement because of it is smaller than the Bohr radii of CdS (2.8 nm) and CdSe (4.9 nm). Raman spectra show two dominant vibrational bands about 208 and 415 cm⁻¹ associated at CdSe-1LO-like and CdSe-2LO-like. By transmittance measurements at room temperature are found that the optical band gap energies vary from 1.86 to 2.16 eV in the range of investigated sulphur molar fraction. Room temperature photoluminescence shows radiative bands in the visible range and a dominant band in the UV range, approximately 3.0 eV, which can be associated with a radiative transition, bound exciton to donor impurity.     

Optical characterization of CdS semiconductor nanoparticles capped with starch

Starch capped cadmium sulfide (CdS) nanoparticles were synthesized by aqueous solution precipitation. Starch added during the synthesis of nanoparticles resulted in cadmium-rich nanoparticles forming a stable complex with starch. The size of the CdS quantum dots was measured using high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The average diameter (d) of nanoparticles spanned the range 4.8 ± 0.4 to 5.7 ± 0.2 nm when the pH of the solution was varied within the range 10-14. The main Raman phonon of CdS, the longitudinal optical mode located around 300 cm⁻¹, softens as diameter decreases, in accordance with theoretical predictions. In addition, the largest Raman response of starch, near 478 cm⁻¹, related with the important skeletal vibration modes of the starch pyranose ring, dominates the spectra of the CdS capped nanoparticles and also softens as the size decreases. This fact indicates a strain variation on CdS as a function of d which increases as the pH increases.     

Microstructural, optical and photocatalytic properties of CdS doped TiO2 thin films

CdS doped TiO₂ thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO₂ structure. The microstructure parameters of the films such as crystallite size (D_ν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of E_g^opt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO₂. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO₂, although they have lower band gap. The CdS doped TiO₂ could have a better impact on the decomposing of organic wastes.