Polyaniline–CdS nanocomposites: effect of camphor sulfonic acid doping on structural, microstructural, optical and electrical properties

Nanocomposites of CdS nanocrystals with conducting polyaniline doped with camphor sulfonic acid (CSA) have been prepared by spin coating technique and investigated by X-ray diffraction, field emission scanning electron microscopy (FESEM), fourier transform infra red spectroscopy (FTIR), UV–visible spectroscopy and electrical transport method. The X-ray diffraction patterns showed broad peaks due to formation of nanoparticles of CdS in polyaniline matrix. FESEM showed that the transformation of morphology from agglomeration to nanopetals. The FTIR spectra confirmed the interaction between CSA and polyaniline (PANi)–CdS nanocomposite. The UV–visible spectrums revealed the enhancement of doping level for the PANi–CdS nanocomposites which is assigned to the existence of greater number of charges on the polymer backbone. DC electrical conductivity studies showed an increase in conductivity of PANi–CdS nanocomposites from 6.9?×?10^?6 to 3.14?×?10^?4 due to addition of CSA (10–50?%).     

巯基包覆CdSe和CdSe/CdS核壳纳米晶的水相合成与表征

利用水相合成的方法制备了巯基包覆的具有较高荧光量子产率的CdSe和CdSe／CdS纳米晶．水相合成方法的优点是原料低廉、安全可靠和重复性高，缺点是纳米晶的尺寸分布较宽，发光效率不是很高．采用X-射线粉末衍射、吸收和荧光等光谱手段对纳米晶的平均尺度、粒径分布、晶体结构及发光特性进行了表征。在77K到300K的温度范围内，随着温度降低，CdSe纳米晶的发光峰逐渐蓝移，而CdSe／Cds纳米晶发光峰位基本不随温度变化而变化．此外，在325nm激光辐照下，CdSe／CdS纳米晶的荧光寿命比CdSe纳米晶延长了6倍左右，稳定性大幅度提高．以上结果表明，核壳结构的CdSe／CdS纳米晶具有较高的发光效率和良好的稳定性，具有广阔的应用前景．     

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.     

Hybrid nanocomposites based on luminescent colloidal nanocrystals in poly(methyl methacrylate): spectroscopical and morphological studies

We report on preparation process and optical characterization of a nanocomposite material obtained dispersing colloidal semiconductor nanocrystals (NCs), namely CdS and CdSe@ZnS core-shell system in poly(methyl methacrylate) (PMMA). Such method allows a large flexibility on nanocrystal materials and on the choice of the polymer characteristics. Nanocomposite thin films were extensively investigated by means optical and morphological techniques. The effects on NC composition, concentration, size, and surface chemistry on the spectroscopical and structural behaviour of the nanocomposite properties were studied. The NC size dependent optical properties of the nanocomposites are mainly accounted by the NC composition and size, while the morphology of the films is explained on the base of the NC surface characteristics and their concentration in the nanocomposites.     

Rare‐Earth‐Element‐Ytterbium‐Substituted Lead‐Free Inorganic Perovskite Nanocrystals for Optoelectronic Applications

Lead‐(Pb‐) halide perovskite nanocrystals (NCs) are interesting nanomaterials due to their excellent optical properties, such as narrow‐band emission, high photoluminescence (PL) efficiency, and wide color gamut. However, these NCs have several critical problems, such as the high toxicity of Pb, its tendency to accumulate in the human body, and phase instability. Although Pb‐free metal (Bi, Sn, etc.) halide perovskite NCs have recently been reported as possible alternatives, they exhibit poor optical and electrical properties as well as abundant intrinsic defect sites. For the first time, the synthesis and optical characterization of cesium ytterbium triiodide (CsYbI₃) cubic perovskite NCs with highly uniform size distribution and high crystallinity using a simple hot‐injection method are reported. Strong excitation‐independent emission and high quantum yields for the prepared NCs are verified using photoluminescence measurements. Furthermore, these CsYbI₃ NCs exhibit potential for use in organic–inorganic hybrid photodetectors as a photoactive layer. The as‐prepared samples exhibit clear on–off switching behavior as well as high photoresponsivity (2.4 × 10³ A W^?1) and external quantum efficiency (EQE, 5.8 × 10⁵%) due to effective exciton dissociation and charge transport. These results suggest that CsYbI₃ NCs offer tremendous opportunities in electronic and optoelectronic applications, such as chemical sensors, light emitting diodes (LEDs), and energy conversion and storage devices.     

Third-order optical nonlinearity and figure of merit of CdS nanocrystals chemically stabilized in spin-processable polymeric films

We report figure of merit for sub-picosecond nonlinearity at 815 nm for nanocrystals of CdS dispersed in poly(methyl methacrylate) (PMMA). CdS nanocrystals were successfully transferred from the aqueous to the organic phase and stabilized in PMMA films using a new chemical route. We report a nonlinear Kerr coefficient n ₂ of –(8.4 ± 0.4) × 10^–14 cm²/W, and a one-photon figure of merit W = 1.2 for 3 wt% CdS-doped PMMA film. The results suggest the combined processibility and promising optical properties of such materials for use in transmission-mode optical switching and limiting devices based on ultrafast nonlinearity.     

Preparation and characteristics of CdS thin films by dip-coating method using its nanocrystal ink

CdS nanocrystals were synthesized by hot injection method using EG as solvent, polyvinylpyrrolidone as dispersant, triethanolamine as stabilizing agent, Cd(NO₃)₂·4H₂O and H₂NCSNH₂ as cadmium and sulfur sources respectively. The synthesized nanocrystals were washed and ultrasonically dispersed with absolute ethanol to prepare nanocrystal ink. CdS thin films were deposited by dip-coating glass substrates with the nanocrystal ink and annealed at 450 °C in Ar atmosphere. Crystalline phase, morphology and element stoichiometry of the CdS nanocrystals derived from different synthesis temperatures were investigated by XRD, TEM and EDS. Surface morphology, crystalline phase and optical absorption spectrum of the CdS films were characterized by SEM, XRD and UV-Vis.     

Generalized chemical route to develop fatty acid capped highly dispersed semiconducting metal sulphide nanocrystals

This work deals with the synthesis of highly dispersed semiconducting nanocrystals (NCs) of cadmium sulphide (CdS), zinc sulphide (ZnS) and lead sulphide (PbS) through a simple and generalized process using oleic acid (OA) as surfactant. To synthesize these NCs, metal–oleate (M–O) complexes were obtained from the reaction at 140 °C between metal acetates and OA in hexanes media. Subsequently, M–O complexes were sulphurized using thioacetamide at the same temperature. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations show that the synthesized products are of nanoscale-size with highly crystalline cubic phase. The optical absorption of OA-capped metal sulphide NCs confirms that their size quantization induced a large shift towards visible region. Photoluminescence (PL) spectrum of CdS NCs shows a broad band-edge emission with shallow and deep-trap emissions, while PL spectrum of ZnS NCs reveals a broad emission due to defects states on the surface. The thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy indicate that fatty acid monolayers were bound strongly on the nanocrystal surface as a carboxylate and the two oxygen atoms of the carboxylate were coordinated symmetrically to the surface of the NCs. The strong binding between the fatty acid and the NCs surface enhances the stability of NCs colloids. In general, this generalized route has a great potential in developing nanoscale metal sulphides for opto-electronic devices.     

In situ synthesis of transparent fluorescent ZnS–polymer nanocomposite hybrids through catalytic chain transfer polymerization technique

We report the controllable synthesis of zinc sulfide (ZnS) nanocrystals (NCs)/polymer transparent nanocomposite hybrids in situ based on the catalytic chain transfer polymerization (CCTP) technique. Firstly, a polymeric ligand PMAA [PMAA = poly(acrylic acid)] with controllable low-molecular-weight and a terminal double bond was synthesized through CCTP. Secondly, with the use of this versatile polymeric ligand containing a large number of anchors as the stabilizer, the ZnS NCs were fabricated. Finally, the surface polymeric ligands containing terminal double bonds were copolymerized with methyl methacrylate monomer to form NCs–polymer hybrids through free radical polymerization. The properties of as-prepared ZnS NCs and their nanocomposite hybrids were thoroughly investigated by Fourier transform Raman spectra, Fourier transform infrared spectrum, transmission electron microscope, ultraviolet–visible, photoluminescence, and thermogravimetric analyses measurements. The spectroscopic studies reveal that ZnS–polymer nanocomposite hybrids have good optical properties.     

Nanocrystalline filler induced changes in electrical and stability properties of a polymer nanocomposite electrolyte based on amorphous matrix

An ion conducting polymer nanocomposite electrolyte (PNCE) series of film based on an amorphous polymer host (PMMA)–lithium salt (LiClO₄) complex dispersed with nanocrystalline yttria stabilized zirconia (n-YSZ) is reported. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis have confirmed feasibility of interaction among composite components (i.e. polymer–ion–filler). Ions in the PNCE matrix are present in the form of both free cations/anions as well as contact ion pairs and their concentration depends on filler loading in the matrix. Electrical conductivity enhancement on n-YSZ dispersion occurs by ~2 orders of magnitude at 30 °C and by ~5 orders of magnitude at 100 °C when compared with room temperature conductivity of the undispersed polymer salt (PS) film. The highest achieved conductivity value is ~1.3 × 10⁻⁴ S cm⁻¹ at 100 °C for 2 wt% n-YSZ. An excellent correlation between variation of d.c. conductivity and free mobile charge carriers versus filler loading has been observed. This correlation has been attributed to filler-induced polymer–ion–filler interaction. These evidences have formed the basis to propose a mechanism for ion transport.     

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.     

The role of the surface ligand in the optical properties of CdS quantum dots in poly(vinyl alcohol) matrix

The synthesis and characterization of CdS nanoparticles prepared in poly(vinyl alcohol) (PVA) in situ, to produce a series of CdS/PVA nanocomposite films, is described in this paper. The role of 2-mercaptoethanol as the surface ligand for the nanoparticles has been investigated. Different molar concentrations of the cadmium precursor have also been evaluated, aiming at the preparation of stable aqueous colloidal systems and polymeric films. UV–visible (UV–Vis) and photoluminescence spectroscopies together with scanning electron microscopy and transmission electron microscopy have been used for characterization of the growth kinetics and the relative stability of CdS nanocrystals in the polymeric matrix. The results clearly indicate the formation of hexagonal CdS nanoparticles embedded in the PVA matrix. PVA was not effective in stabilizing colloidal CdS nanoparticles against aggregation. However, it leads to a displacement of the first optical transition of CdS due to compressive deformation effect. The combination of PVA with 2-mercaptoethanol as surface ligands had a strong effect on the optical properties of the resulting embedded CdS nanoparticles.     

Analysis of organometallics dispersed polymer composite irradiated with oxygen ions

Thin films of polymethyl methacrylate (PMMA) were synthesized. Ferric oxalate was dispersed in PMMA films. These films were irradiated with 80 MeV O⁶⁺ ions at a fluence of 1×10¹¹ ions/cm². The radiation induced changes in electrical conductivity, Mössbauer parameter, microhardness and surface roughness were investigated. It is observed that hardness and electrical conductivity of the film increases with the concentration of dispersed ferric oxalate and also with the fluence. It indicates that ion beam irradiation promotes (i) the metal to polymer bonding and (ii) convert the polymeric structure into hydrogen depleted carbon network. Thus irradiation makes the polymer harder and more conductive. Before irradiation, no Mössbauer absorption was observed. The irradiated sample showed Mössbauer absorption, which seems to indicate that there is significant interaction between the metalion and polymer matrix. Atomic force microscopy shows that the average roughness (R _a) of the irradiated film is lower than the unirradiated one.     

Synthesis of CdS-Au2S-Au hybrid dendritic nanostructures

The hybrid CdS-Au₂S-Au dendritic nanocrystals were synthesized in toluene solution at 70 °C. UV-vis and photoluminescence (PL) spectra recorded the optical properties of hybrid nanostructures, which showed an obvious blue shift relative to the absorption peak of CdS dendritic nanocrystals. The initial CdS dendritic nanocrystals exhibited band gap and trap state emission, both of which were quenched by Au parts. Analysis of the hybrid nanostructures by XRD shows the presence of appreciable amounts of Au₂S, indicating that the chemical process involving cation exchanges between Au⁺ ions and Cd²⁺ ions was found.     

不同壳层的CdS／ZnS核／壳结构量子点的温度相关荧光性质

报导了CdS／ZnS纳米晶体（NCs）的制备过程和其光学}生质。通过采用连续离子层吸附和反应技术（SILAR）,我们用少量的表面活性剂合成了不同壳层的四个样品,包括CdS核纳米晶以及具有1～3层ZnS壳的CdS／ZnS核／壳结构纳米晶体样品。发现具有一层ZnS壳的CdS／ZnS样品的荧光量子产率大约比未包覆壳层的CdS纳米晶体样品的强11倍。另外,随着壳层的增加（增至两到三层）,荧光量子产率呈现下降的趋势。对样品进行了温度相关的光谱测量,发现CdS／ZnS和CdS一样具有特殊的光学特性。     

Effect of sonication time on the synthesis of the CdS nanoparticle based multiwall carbon nanotube – maleic anhydride – 1-octene nanocomposites

Effect of sonication time on the synthesis of the CdS nanoparticles within the matrix obtained through the covalent functionalization of multiwall carbon nanotube (MWCNT) with maleic anhydride (MA) – 1-octene copolymer was investigated. Cadmium chloride and thiourea were used as the raw materials. MWCNTs used for the matrix were synthesized by Catalytic Chemical Vapor Deposition using Fe-Co/Al₂O₃ as the catalyst. The obtained nanostructures were characterized by FTIR, XRD, Raman spectroscopy, TEM, SEM, TG and UV-Vis spectroscopy. Electrophysical properties of the polymer nanocomposites obtained using different periods of time for sonication were comparably investigated. The average CdS particle diameter was between 3.9–7.9 nm as confirmed independently by TEM and XRD. UV-Vis spectroscopy revealed that the obtained nanostructures are appropriate base materials for making optical devices.     

Effect of ion beam irradiation on metal particle doped polymer composites

Polymethyl methacrylate (PMMA) was prepared by solution polymerization method. Different concentrations (10, 20 and 40%) of Ni powder were dispersed in PMMA and the composite films were prepared by casting method. These films were irradiated with 120 MeV Ni^10 + ions at a fluence of 5 × 10¹² ions/cm². Electrical, structural and chemical properties of the composites were studied by means of an LCR meter, X-ray diffraction, FTIR spectroscopy and SEM/AFM, respectively. The results showed that the conductivity increases with metal concentration and also with ion beam irradiation. This reveals that ion beam irradiation promotes the metal/polymer bonding and converts polymeric structure into hydrogen depleted carbon network. It was observed from XRD analysis that percentage crystallinity and crystalline size decrease upon irradiation. This might be attributed to rupture of some polymeric bonds, which is also corroborated with FTIR spectroscopic analysis. Ion beam tempts graphitization of polymeric material by emission of hydrogen and/or other volatile gases. Surface morphology of the pristine and irradiated films was studied by atomic force microscopy (AFM)/scanning electron microscopy (SEM). Result showed that the surface roughness increases after ion beam irradiation.     

Surface passivation of CdS/Zn2SiO4 nanocomposites prepared by a wet chemical route

Highly luminescent CdS/Zn2SiO4 nanocrystals were prepared by a wet chemical method. The effect of surface passivation was observed in photoluminescence measurements of CdS nanocrystals embedded in colloidal nanocrystallite or amorphous Zn2SiO4 matrix. The resultant luminescent emission of as-prepared CdS/Zn2SiO4 nanocomposite thin films displays two distinct components. One is attributed to the band-edge emission and the other is due to the surface defects. The effect of aging on CdS/Zn2SiO4 nanocomposite thin films has been investigated, showing the active role of Zn2SiO4 matrix in modifying the surface states.     

Synthesis and optical properties of water-soluble fluoride nanophosphors co-doped with Eu and Tb

The synthesis, structure and optical properties of water-soluble fluoride nanophosphors co-doped with Eu³⁺ and Tb³⁺ are presented. Nanocrystals of NaYF₄ were synthesized via a hydrothermal microwave-assisted technique. XRD, TEM, AFM, FTIR as well as photoluminescence (PL) spectra were used to characterize the doped nanocrystals. The average size of nanocrystals, determined from XRD, AFM and TEM measurements, was ca. 28 nm. It was found that energy transfer occurs between Tb³⁺ and Eu³⁺ ions embedded in NaYF₄ matrix, both in nanocrystals dispersed in chloroform and those in aqueous solution. We demonstrate that this simple colloidal system possesses the essential features required for both energy transfer and potential application in biolabeling.     

Dielectric and pyroelectric properties of a composite of ferroelectric ceramic and polyurethane

Flexible piezo- and pyroelectric composite was made in the thin film form by spin coating. Lead Zirconate Titanate (PZT) ceramic powder was dispersed in a castor oil-based polyurethane (PU) matrix, providing a composite with 0–3 connectivity. The dielectric data, measured over a wide range of frequency (10^–5 Hz to 10⁵ Hz), shows a loss peak around 100 Hz related with impurities in the polymer matrix. There is also an evidence of a peak in the range 10^–4 Hz, possibly originating from the glass transition temperature T_g of the polymer. The pyroelectric coefficient at 343 K is 7.0×10^–5 C·m^–2·K^–1 which is higher than that of β-PVDF (1×10^–5 C·m^–2·K^–1). Electronic Publication