Nanocrystal CdS Research Articles

Investigation of structural, spectral, optical and nonlinear optical properties of nanocrystal CdS: Electrodeposition and quantum mechanical studies

Nanocrystalline CdS semiconductor was synthesized by electrodeposition technique, and characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), and FTIR spectroscopic methods. XRD analysis result showed that it is a hexagonal crystal structure. SEM micrographs showed that the CdS nanocrystal is homogeneously distributed on the surface. The roughness of the CdS thin films was measured by AFM. The presence of band in the FTIR spectrum at 558 cm−1 corresponds to the stretching of CdS. CdS nanocrystals were modeled separately and calculated in the Gaussian program. Structural, spectroscopic, and nonlinear optical (NLO) properties were investigated using the DFT/Lanl2dz and semi-empirical/pm6 level. Besides, by making energy calculations, Homo, Lumo, band gap, and total state density (TDOS) were calculated. The experimental band gap was measured at 2.40 eV, while this calculated for hexagonal and cubic structure as 2.21 and 2.01 eV with semiemprical/pm6 model, 2.44 and 2.25 eV with DFT/lanl2dz level.These results support that CdS nanostructures are crystallized in hexagonal structure. With this study, the obtaining of nano structured CdS films by electrodeposition method, their structural, optical and surface properties were experimentally examined, supported by theoretical calculations, and additionally NLO properties were investigated. It has been determined that the nanocrystals obtained are suitable material for optoelectronic applications.

Engineering of colloidal nanocrystal thin films and their optoelectronic properties: A simple and effective route

This work investigates the effect of heat treatments on CdSe/CdS core–shell nanocrystals assemblies with different sizes and capping ligands. Nanostructured thin films, consisting of an array of CdSe quantum dots embedded in a continuous matrix of CdS, have been obtained by mild thermal treatments of CdSe/CdS core–shell nanocrystals deposited on glass substrates from colloidal solution. These materials are regarded as promising photon upconverters, or absorbers for high-efficiency photovoltaic devices. The treatments were conducted in the range 300–550 °C for up to 150 min. The nanoscale evolution during the heat treatment was investigated by monitoring optical properties of the films. Initially, the well-defined photoluminescence band, corresponding to the first quantum dots exciton state, rapidly shifts towards lower energy, indicating delocalization of the exciton and suggesting that nanocrystal CdS shells are merging by sintering mechanisms, thus forming a continuous matrix. Control over this phase of the heat treatment leads to the desired nanoscale morphology and properties. The kinetics of sintering has been characterized, and the procedure has been systemically applied to CdSe/CdS nanocrystals of different sizes and ligand types. This research provides novel values for the activation energy of the sintering process and strongly support the general applicability of such process to control and optimize optoelectronic properties of nanostructured thin films for applications like light-emitting diodes, tunable emitters and photoconductors among others.

The Effect of Shallow Impurities on the Light Absorption by the Nanocrystals CdS

The energy of quantum transitions of exciton-impurity states in a heterosystem with nanocrystals is calculated. The absorption spectra associated with the indicated transitions are analyzed. It is qualitatively shown that broad luminescence bands in the red region are related to the impurity acceptor states, and the high narrow ones in the violet region to pure excitonic states and excitonic states interacting with the ion of a donor. The satisfactory quantitative agreement of our calculations with experimental data for high energy luminescence bands is obtained.

White electroluminescence from a prototypical light-emitting diode based on CdS/Si heterojunctions

CdS/Si heterojunctions have been synthesized through growing nanocrystal CdS on the porous polysilicon by using a chemical bath deposition. The prototypical light-emitting diode (LED) based on CdS/Si heterojunctions, which shows an obvious rectification behavior, has been constructed. White electroluminescence (EL) from this prototypical LED can be observed under the forward bias with ∼4.0V, which is broad and ascribed to the nanocrystal silicon, the band gap emission and the defect levels emissions of nanocrystal CdS. Through controlling the forward bias, the chromaticity coordinate, correlative color temperature and color rendering index of white EL can be purposefully tuned. The physical properties obtained indicate that this prototypical LED based on CdS/Si heterojunctions ought to be as a potential candidate for the application in the field of white light-emitting diodes.

Temperature-dependent photoluminescence from CdS/Si nanoheterojunctions

CdS/Si nanoheterojunctions have been fabricated by growing nanocrystal CdS (nc-CdS) on the silicon nanoporous pillar array (Si-NPA) through using a chemical bath deposition method. The nanoheterojunctions have been constructed by three layers: the upper layer being a nc-CdS thin films, the intermediate layer being the interface region including nc-CdS and nanocrystal silicon (nc-Si), and the bottom layer being nc-Si layer grown on sc-Si substrate. The room temperature and temperature-dependent photoluminescence (PL) have been measured and analyzed to provide some useful information of defect states. Utilizing the Gauss–Newton fitting method, five emission peaks from the temperature-dependent PL spectra can be determined. From the high energy to low energy, these five peaks are ascribed to the some luminescence centers which are formed by the oxygen-related deficiency centers in the silicon oxide layer of Si-NPA, the band gap emission of nc-CdS, the transition from the interstitial cadmium (ICd) to the valence band, the recombination from ICd to cadmium vacancies (VCd), and from sulfur vacancies (Vs) to the valence band, respectively. Understanding of the defect states in the CdS/Si nanoheterojunctions is very meaningful for the performance of devices based on CdS/Si nanoheterojunctions.

Synthesis, structures and optical properties of CdS:Cd/Si multi-interface nanoheterojunction

CdS/Si multi-interface nanoheterojunction is synthesized through depositing nanocrystals CdS (nc-CdS) on the silicon nanoporous pillar array (Si-NPA) using a chemical bath deposition method. p-type nanocrystals Si in Si-NPA and n-type nc-CdS construct the multi-interface nanoheterojunction. Due to the reducibility of Si-NPA, a portion of Cd2+ in the interface of Si-NPA and solution are deoxidized and nanocrystals Cd are simultaneously incorporated into the interface of Si–CdS, namely, CdS:Cd/Si-NPA. Through decomposing the resolution XPS spectrum of Cd 3d, the ratio of Cd0 and Cd2+ is about 0.7:1. Three primary color emissions from CdS:Cd/Si-NPA are observed at the room temperature. Optical band gap obtained by the Tauc’s relation and origins of emission bands are studied.

One-Step High-Temperature Solvothermal Synthesis of TiO2/Sulfide Nanocomposite Spheres and Their Solar Visible-Light Applications

A one-step high-temperature hydrated-sulfate assisted solvothermal method has been developed to synthesize TiO(2)/sulfide nanocomposite spheres. Different hybrid spheres of TiO(2)/CdS, TiO(2)/Cu(2)S, TiO(2)/FeS, TiO(2)/Co(9)S(8), and TiO(2)/ZnS were readily prepared by exploiting different hydrated sulfate. The hydrated sulfate has been proved to play multifunctional roles during the synthetic process, such as spherical template, water supplier, and composition controller. Nanocrystal CdS can be reduced from CdSO(4) at a high solvothermal temperature of 350 °C, and the TiO(2)/CdS nanocomposite spheres prepared by this method exhibit superior visible-light-driven photocatalytic efficiency because of its effective heterointerface and high crystallinity.

Thermal decomposition of [bis(salicylaldehydato)cadmium(II)] to CdS nanocrystals

The present investigation reports, the novel synthesis of nanocrystals CdS using thermal decomposition of [bis(salicylaldehydato)cadmium(II)], as a new precursor, and elemental sulfur in oleylamine. The as-synthesized CdS crystals have diameters about 10 nm. The products were characterized by X-ray diffraction (XRD) transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–Vis) spectroscopy and Fourier transformed infrared (FT-IR) spectra. The results of this paper show that the shape and size of cadmium sulfide nanocrystals can be controlled systematically by adjusting certain reaction parameters, such as the reactant concentration, the reaction temperature and the reaction time. Cadmium sulfide nanoparticles and nanorods with different lengths have been successfully prepared.

Microstructure and thermal properties of (1−x) As2S3−xCdCl2 glassy system

The homogenous glass samples of the (1−x) As2S3−xCdCl2 where x=0 and 0.05 were prepared by the conventional melt-quenched method. The addition of 5 mol% CdCl2 enhanced the glass transition temperature of pure As2S3 glass sample by about 30°C. Based on the experimental data, the microstructure is considered to be that the discrete molecule species of AsCl3 and nanocrystal CdS is homogeneously dispersed in the disordered polymer network formed by AsS3 pyramids interconnected by sulfur bridges.