Preparation and optical study of CdS nanocrystals embedded phosphate glass

A new phosphate glass system with CdS nanocrystals dispersed in glass matrix was investigated. The phosphate glass composition with good stability has been used for preparation of CdS doped glasses. The CdS in the range of 0.5-7.0% has been doped into this glass composition. Effect of CdS content on the optical and other properties has been investigated. The optical characterization of the glass samples showed that with increasing concentration of CdS, there was a red shift in transmission cut-off of the glasses. From the transmission cut-off of each glass sample, the band gap of the CdS nanocrystals embedded glass was calculated. The band gap of CdS particles embedded glass was observed in the range of 3.1-4.1 eV. The present system is compared with CdS nanocrystals doped in silica based glass system. In the phosphate glass system, the UV transmission cut-off's are not sharp and the optical transmittance decreases with increasing CdS content in contrast to silica glass system. The reason for such behavior has been discussed in the present investigation. TEM of the CdS doped phosphate glasses showed CdS particle size in the range of 5-7 nm for lower concentration of CdS and 10-100 nm for higher concentration of CdS. The nanocrystals are non-uniform in size but uniformly dispersed in glass matrix.     

Synthesis and characterization of CdS nanocrystals stabilized in polyvinyl alcohol–sodium polyphosphate

Nanocrystals of cadmium sulfide have been synthesized in a series of aqueous solutions with a fixed concentration of polyvinyl alcohol and a variable amount of sodium polyphosphate. Optical absorption and photoluminescence measurements have been performed in order to determine the optical properties of the colloidal solutions. Transmission electron microscopy has been used to obtain structural information of the nanocrystals. The results show two different behaviors as the amount of sodium polyphosphate is increased in the solutions. The photoluminescence of nanocrystals in a polyvinyl alcohol solution without sodium polyphosphate is quenched. The addition of this co-stabilizer activates the luminescence, being more intense and blue-shifted as the amount of sodium polyphosphate is increased. However, further additions of this product beyond a sodium polyphosphate–polyvinyl alcohol weight ratio of 6.25 · 10^? 3:1 leads to the inverse behavior. Transmission electron microscopy measurements indicate that a deagglomeration of the particles is produced as the amount of sodium polyphosphate is increased.     

Swift heavy ion irradiation effect on Cu-doped CdS nanocrystals embedded in PMMA

Semiconductor nanocrystals (NCs) have received much interest for their optical and electronic properties. When these NCs dispersed in polymer matrix, brightness of the light emission is enhanced due to their quantum dot size. The CdCuS NCs have been synthesized by chemical route method and then dispersed in PMMA matrix. These nanocomposite polymer films were irradiated by swift heavy ion (SHI) (100 MeV, Si⁺⁷ ions beam) at different fluences of 1 × 10¹⁰ and 1 × 10¹² ions/cm² and then compared their structural and optical properties by XRD, atomic force microscopy, photoluminescence, and UV-Vis spectroscopy before and after irradiation. The XRD spectra showed a broad hump around 2θ ≈ 11·83° due to amorphous PMMA and other peaks corresponding to hexagonal structure of CdS nanocrystals in PMMA matrix. The photoluminescence spectra shows a broad peak at 530 nm corresponding to green emission due to Cu impurities in CdS. The UV-Vis measurement showed red shift in optical absorption and bandgap changed from 4·38–3·60 eV as the irradiation fluency increased with respect to pristine CdCuS nanocomposite polymer film.     

Characterization of CdS nanocrystals embedded in KCl single crystal matrix grown by Czochralski method

The growth of CdS nanocrystals (NCs) embedded in bulk KCl single crystal matrix is performed using the Czochralski method. The X-ray diffraction reveals the incorporation of the CdS NCs with a cubic structure inside the KCl matrix. The optical density measurements of the CdS NCs embedded in KCl single crystal show a shift of the absorption edge towards higher energies. The optical band-gap is estimated to be about of 2.60 eV. The photoluminescence (PL) spectrum of the studied samples presents four emission bands in the range of 2.20–2.56 eV.     

Luminescence in Mn-doped CdS nanocrystals

We have synthesized Mn-doped CdS nanocrystals (NCs) with size ranging from 1.8–3 nm. Photoluminescence (PL) spectra of the doped NCs differ from that of the undoped NCs with an additional peak due to Mn d-d transitions. Electron paramagnetic resonance spectra along with X-ray absorption spectroscopy and PL spectra confirm the incorporation of Mn in the CdS lattice. The fact that emissions from surface states and the Mn d levels occur at two different energies, allowed us to study the PL lifetime decay behaviour of both kinds of emissions.     

Synthesis of nearly monodispersive gold nanoparticles by a sodium diphenylamine sulfonate reduction process

Au nanoparticles have been prepared by the reaction of HAuCl₄ and sodium diphenylamine sulfonate in the presence/absence of poly(vinylpyrrolidone)(PVP) at room temperature. The nanoparticles were characterized by Transmission electron microscopy (TEM), UV-Vis absorption spectrum. The research showed that the molar ratio of PVP/ HAuCl₄ has effect on the size and the morphology of Au nanoparticles.     

Thermokinetic study on growth process of CdS nanocrystals by in situ microcalorimetry

In situ microcalorimetry was used to investigate the energy evolution during CdS nanocrystal growth process. It can provide important information for controlling crystal growth. The CdS nanospheres were synthesized in the glycol-water system at room temperature. The energy change of CdS nanocrystal growth process was measured by a microcalorimeter. The microcalorimetric curve shows a strong exothermic peak. On the basis of the experimental result, the rate constant and the activation Gibbs energy have been obtained. The CdS nanocrystals were characterized by X-ray diffraction, scanning electron microscope and photoluminescence spectra. The morphology evolution can be well connected with the energy change.     

功能化CdS纳米晶的制备

以氯化镉和硫化钠为原料,2-巯基乙醇(ME)为有机配体,成功制备了粒径可控的、表面富有羟基的CdS纳米晶.采用不同的ME/Cd2 及H2O/DMF比例以观察有机配体及溶剂对生成粒子尺寸的影响.透射电子显微图证实了球形CdS纳米粒子很好地分散在H2O/DMF溶液中,没有任何团聚现象发生.傅立叶变换红外谱图(FT-IR)显示了羟基基团成功地包覆在纳米晶的表面.X线衍射(XRD)测试揭示了功能化CdS纳米晶的晶形主要为立方晶.     

Thermally stimulated discharge currents in polyvinyl pyrrolidone polymer films

Polyvinyl pyrrolidone films of thickness 17.6 μm were grown by the isothermal solution growth technique. Thermally stimulated discharge currents were studied on these films as a function of polarizing field strength and polarizing temperature, at a constant heating rate of 0.14 Ks⁻¹. In all these studies only one TSDC peak was observed and the temperature corresponding to this peak was found to show weak but definite dependence on the polarizing field strength and polarizing temperature. The activation energies and relaxation parameters and charge associated with this peak were evaluated. The origin of TSDC was attributed to the space charge process.     

Refractive index of silver nanoparticles dispersed in polyvinyl pyrrolidone nanocomposite

A silver nanoparticles/polymer composite was fabricated by reduction of silver nitrate in the presence of the polymer polyvinyl pyrrolidone. The plasmonic resonance of silver nanoparticles leads to a remarkable change of the dielectric dispersion of the polymer in the visible range. The refractive indexes of the nanocomposite with different fractions of the precursor silver nitrate at the wavelengths of 488, 532, and 633 nm were investigated by using reflectometry. At a fraction larger than 0.122, the refractive index change was larger than 0.1, and the maximal refractive index change of 0.84 was achieved at a wavelength of 488 nm with a fraction of 0.422. The experimental results were consistent with the prediction of Maxwell Garnett theory. The solid-state nanocomposite with a strong refractive index dispersion and tunability has promising applications in optics and communication devices.     

水溶性发光硫化镉纳米晶的制备

以氯化镉和硫化钠为原料,巯基乙酸为有机配体,水为溶剂,制得表面羧基化的CdS纳米晶。利用FTIR、XRD、UV-vis、荧光光谱(PL)考察了CdS纳米晶的结构与性能。结果表明,羧基基团包覆在纳米晶表面,所制得的CdS纳米晶以立方晶型为主,电子-空穴对复合引起的表面发射和硫空位引起的缺陷发射共同作用,使得CdS纳米晶在紫外光照射下发出明显的黄光,表现出良好的光致发光性能。     

Electrical conduction mechanism in solution grown doped polyvinyl pyrrolidone films

A detailed study of electrical conduction mechanism in bimetallized ferrocene-doped polyvinyl pyrrolidone films was carried out. The measurements were carried out on films of about 20 μm thick, in the field range of (2.0–8.0) x 10⁴ V/cm at temperatures ranging from 363 to 423 K. An investigation of the effect of impurity such as ferrocene in the polymer matrix was undertaken. Lowering of activation energy and increase in current due to doping were observed. The results showed that the charge carriers were generated by field-assisted lowering of coulombic barriers at the traps and were conducted through the bulk of the material by a hopping process between the localized states by a Jonscher-Ansari modified Poole-Frenkel mechanism. The dependence of current and activation energy on the ferrocene concentration is explained on the basis of charge transfer type of interaction between dopant and polymeric material.     

Synthesis of nearly monodisperse embedded nanoparticles by separating nucleation and growth in ion implantation

We investigate the formation of nanoparticles of Au in SiO(2) by multiple ion implantation steps and intermediate anneals to isolate nucleation and growth, thereby producing a narrow particle size distribution. We discuss the effects of varying the initial nucleation dose and the growth temperature and establish guidelines for synthesizing nanoparticles with improved size uniformity. By this method, we have obtained a standard deviation of 16% on an average diameter of 1.68 nm, compared to 28% when no attempt is made to isolate nucleation and growth.     

Surfactant-dependent photoluminescence of CdTe/CdS nanocrystals

ABSTRACT

The photoluminescence of aqueously synthesised core/shell CdTe/CdS quantum dots (QDs) was investigated. Two molar ratios (2.4 and 1.3) of thioglycolic acid (TGA) to Cd²⁺ were compared to determine the best synthesis conditions for high photoluminescent quantum yield (PLQY) and photostability. A difference in the PLQY of the CdTe/CdS QDs was observed when CdS shells were grown with different TGA/Cd²⁺ ratios. The difference in the observed PLQY was attributed to the quality of the passivation of the CdTe during the CdS shell growth. At TGA/Cd²⁺ ratio of 1.3, the CdS shell forms through homogeneous nucleation, which is limited by diffusion of growth material from the solution onto the QDs surface. Due to the lattice mismatch of CdTe and CdS, the core will experience coherence strain resulting in dislocation sites and surface defects between nucleation sites which can result in non-radiative trap states. When the TGA/Cd²⁺ ratio is 2.0, the CdS shell grows epitaxially, minimising the number of surface trap states. Finally, we observed that the fluorescence intermittency was supressed for CdTe QDs after UV light illumination, attributed to annealing of deep surface trap states by UV light.     

Growth of semiconducting nanocrystals of CdS and ZnS

In this work, we report the study of growth of CdS as well as ZnS nanocrystals using in-situ small angle X-ray scattering (SAXS) technique, in presence of thio-glycerol as capping agent. We observe that the diameter of the nanocrystal is controlled between 1 and 3 nm by varying the temperature of the reaction. Further, the self-focusing of the size distribution can be observed and is more pronounced at higher temperatures reducing its relative width from 25% to 10%.     

一种无水无氧制备CdS纳米晶的新方法

以醋酸镉和硫为原料,采用二硫化四乙基秋兰姆TETD和2,2-二硫代二苯并噻唑为成核剂,利用无水无氧系统在ODE的溶液中制备了尺寸可控、单分散、均一的半导体CdS纳米材料.采用XRD、粒度分析、SEM技术分别表征产物的结构、粒度和形貌.通过改变两种成核剂的使用量及反应时间可以得到不同粒径的CdS纳米晶.研究表明,在一定范围内,成核剂使用量增加或者反应时间延长都会导致产物的粒度变大,因此通过调节成核荆的使用量和反应时间从而实现对CdS纳米晶的可控生长.     

Synthesis and fluorescence spectrum analysis of CdS nanocrystals

An optimized synthesis route was applied for control the preparation of CdS nanocrystals (NCs) in an aqueous solution. Some key factors which influencing the characters of CdS NCs, such as stabilizers, ratio of reactant etc, were investigated. It was found that the fluorescence (FL) intensity of CdS NCs could be dramatically enhanced by refluxing. The size, shape, crystal structure and the optical properties of CdS NCs were also characterized by TEM, XRD, UV–Vis and FL spectra. The result showed that the well-disperse spheres CdS NCs with 6 nm in diameter were obtained.     

功能化CdS纳米晶的合成及CdS/聚苯乙烯纳米杂化材料的研究

以氯化镉和硫化钠为原料,采用巯基乙醇为有机配体,在H2O/DMF的溶剂中,制得分散均匀且表面富含羟基基团CdS纳米晶溶液.我们使用γ-甲基丙烯氧丙基三甲氧基硅烷(MPS)来修饰CdS纳米晶的表面,得到双键官能团化的CdS纳米晶.通过原位自由基聚合方法,成功地得到了聚苯乙烯基CdS纳米晶复合材料.利用傅里叶红外光谱仪(FT-IR)、透射电子显微镜(TEM)、紫外-可见光吸收光谱仪(UV-vis)、X射线衍射分析仪(XRD)、热重分析仪(TGA)、荧光光谱 (PL) 考察了CdS纳米晶及CdS/聚苯乙烯复合材料的结构和光学性能的关系规律.结果表明巯基乙醇表现出良好的光学性能,其配体不是简单的物理吸附于纳米晶表面,而是以化学键的形式和纳米晶表面镉原子相结合.相比于纯的聚苯乙烯材料,聚苯乙烯基CdS纳米晶材料表现出良好的光学和热学性能.