Novel synthesis of selective phase-shape orientation of AgInS2 nanoparticles at low temperature

In this work, phase- and shape-controlled AgInS2 (AIS) colloidal nanoparticles are synthesized by thermal decomposition of metal xanthate at a temperature of similar to 110 A degrees C in an organic solvent containing surfactant molecules. The spherical tetragonal-shaped AIS was observed when o-dichlorobenzene (DCB) with oleylamine (OLA) and trioctylphosphine (TOP) was used, while rod-shaped AIS with orthorhombic structure was observed in the presence of o-dichlorobenzene with pyridine (PY). The resulting nanoparticles are analyzed by X-ray diffraction (XRD), UV-vis, PL, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) techniques. It is also reported that the AIS nanoparticles (NPs) synthesized in the presence of OLA and TOP show a photoluminescence properties, and their fluorescence emission wavelength can readily be tuned from the ultraviolet (UV) to the visible spectrum region by merely prolonging the reaction time

One-pot synthesis of CuInS2 and CuInS2/MS (M=Cd, Zn) core-shell luminescent nanocrystals: a low-temperature and low-cost approach

The single-pot synthesis of highly crystalline and fluorescent chalcopyrite CuInS2 (CIS) colloidal nanoparticles has been reported by thermal decomposition of metal ethyl xanthate (at similar to 110 degrees C) for the first time. The fluorescence emission wavelength can also be readily tuned from the UV to the visible region by merely prolonging the reaction time, as the PL emission may be varied from 550 to 675 nm. The synthesized CIS is subjected to postdeposition treatment with CdS/ZnS in one pot route using cadmium/zinc xanthate at low temperature (similar to 80 degrees C) to improve the quantum yield of core-shell (CIS/CdS or ZnS) nanocrystallites as compared to CIS core. The stability of core-shell particularly CIS/ZnS system upon continuous laser exposure suggests the formation of surface bonds with superior mechanical stability. This low-cost synthesis of such nontoxic QDs using green chemical routes is a promising approach for the fabrication of optoelectronic and biosensing devices

A solvothermal approach for the size-, shape- and phase-controlled synthesis and properties of CuInS2

In this work, Copper Indium disulfide (CIS) nanoparticles of size similar to 5 nm were prepared via solvothermal approach in ethanol under the nitrogen atmosphere using copper chloride, indium chloride and thiourea (Tu) as starting materials, without any assistance through organic ligands at the reaction temperature of 150 degrees C. The factors which might affect the morphology, structure, phase of the product during the synthesis were discussed. It was found that the products were significantly affected by the reaction time and solvent. The morphology, structure, phase constituents and optical properties of the as prepared CIS powders were characterized by X-ray diffraction (XRD), Energy dispersive Spectroscopy (EDS), scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) spectrometry respectively. The result shows that the CIS nanoparticles can be synthesized by solvothermal method at a reaction time of 2 h and shows that when the reaction time was increased from 2 h to 48 h, CIS porous flower like nanoparticles were obtained as we increase the reaction time. We also observed that in this process, the phase selection of WZ-CIS or CH-CIS is greatly influence by solvent. We also observed that, in this process sulfur source did not influence the phase but participated in the growth of the nanoparticles

Effect of linker on the photosensitization of ZnO layers with CdSe quantum dots

In this work, zinc oxide (ZnO) nanoparticles (size < 10 nm) were formed via precipitation in ethanolic solution. The zinc acetate and lithium hydroxide solutions in ethanol were mixed at 273 K temperatures under vigorous stirring. To study the effect of quantum dot (QD) coverage, we have prepared a colloidal suspension of capped CdSe QDs (size similar to 5 nm) by chemical route and anchored them to a nanoporous ZnO layer either by direct adsorption or through linker. Here a bifunctional molecule (mercaptopropionic acid, MPA, and thioglycolic acid, TGA) was previously adsorbed on the ZnO surface, which acted as a molecular cable. From TEM/SEM studies, it was observed that direct adsorption of CdSe QDs onto ZnO surface was not efficient. However, the bifunctional linker molecules particularly MPA facilitates binding of CdSe QDs to ZnO; and consequently, interparticle electron transfer is thus facilitated. The use of MPA linker despite of its long carbon chain also aids in the quenching of photoluminescence of CdSe on addition of ZnO in a more systematic manner indicating efficient charge transfer from CdSe into ZnO as compared with the without linker and with linker TGA case, respectively. Due to higher PL quenching and reduction in lifetime values, higher values of Stern-Volmer quenching constants were thus obtained for CdSe-ZnO composites with MPA as compared with TGA linker and without linker case, respectively. Nonlinear Stern-Volmer plots as observed for samples without linker case indicated heterogeneous quenching due to insufficient binding between CdSe QDs and ZnO. By means of spectroscopic (PL, UV-VIS, FTIR) and microscopic (TEM, SEM) techniques, we have demonstrated linker-dependent photosensitization mechanism of ZnO layers with CdSe QDs. Our data thus illustrate that interfacial-electron transfer kinetics in QD-linker-ZnO assemblies are almost independent of the length of alkyl-containing molecular linkers

Effect of linker on the photosensitization of ZnO layers with CdSe quantum dots

In this work, zinc oxide (ZnO) nanoparticles (size < 10 nm) were formed via precipitation in ethanolic solution. The zinc acetate and lithium hydroxide solutions in ethanol were mixed at 273 K temperatures under vigorous stirring. To study the effect of quantum dot (QD) coverage, we have prepared a colloidal suspension of capped CdSe QDs (size similar to 5 nm) by chemical route and anchored them to a nanoporous ZnO layer either by direct adsorption or through linker. Here a bifunctional molecule (mercaptopropionic acid, MPA, and thioglycolic acid, TGA) was previously adsorbed on the ZnO surface, which acted as a molecular cable. From TEM/SEM studies, it was observed that direct adsorption of CdSe QDs onto ZnO surface was not efficient. However, the bifunctional linker molecules particularly MPA facilitates binding of CdSe QDs to ZnO; and consequently, interparticle electron transfer is thus facilitated. The use of MPA linker despite of its long carbon chain also aids in the quenching of photoluminescence of CdSe on addition of ZnO in a more systematic manner indicating efficient charge transfer from CdSe into ZnO as compared with the without linker and with linker TGA case, respectively. Due to higher PL quenching and reduction in lifetime values, higher values of Stern-Volmer quenching constants were thus obtained for CdSe-ZnO composites with MPA as compared with TGA linker and without linker case, respectively. Nonlinear Stern-Volmer plots as observed for samples without linker case indicated heterogeneous quenching due to insufficient binding between CdSe QDs and ZnO. By means of spectroscopic (PL, UV-VIS, FTIR) and microscopic (TEM, SEM) techniques, we have demonstrated linker-dependent photosensitization mechanism of ZnO layers with CdSe QDs. Our data thus illustrate that interfacial-electron transfer kinetics in QD-linker-ZnO assemblies are almost independent of the length of alkyl-containing molecular linkers

Charge Transport and Electrochemical Response of Poly(3,4- ethylenedioxypyrrole) Films Improved by Noble-Metal Nanoparticles

Charge-transport phenomena and redox switching of poly(3,4-ethylenedioxypyrrole) (PEDOP) films embedded with Au and Ag nanoparticles have been investigated. In the bulk, charge transport can be described by an ohmic regime at low voltages and a space-charge-limited current regime at high voltages in PEDOP–Au, which is in contrast to trap-filled domains deduced for neat PEDOP and PEDOP–Ag nanocomposites, all indicating transitions driven by an external bias. This also allowed a direct estimation of a fairly high charge-carrier mobility at room temperature in PEDOP–Au, in addition to a higher donor density, which are advantageous for device applications. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy affirmed the prevalence of Au/Ag nanoparticles as nonleachable entities in PEDOP, thus allowing the movement of electrons through the conducting nanoaparticles during electrochemical switching, an effect that is absent in the neat PEDOP film. Valence-band spectra and optical studies revealed that nanoparticles narrowed the band gap and increased the absorption coefficient of PEDOP, which enhanced the electrochromic switching ability of PEDOP. A coloration efficiency enhancement by an order of magnitude, higher electrochemical charge intercalation capacity, and higher diffusion rates reflect the role of noble-metal nanoparticles in improving the conduction and electrochemical activity of PEDOP

Polymeric stabilization of hybrid nanocomposites: a comparison between in situ and ex situ-grown CuInS2 in poly(3-hexylthiophene) polymer

CuInS2 (CIS) particles were directly synthesized in P3HT matrix with different concentrations ratio of P3HT and CIS (1:2, 1:4, and 1:8) by decomposition of copper indium xanthate (CIX). Here, copper indium xanthate and P3HT were mixed homogeneously in o-dichlorobenzene (DCB), which induced the formation of the CIS nanoparticles by the thermal decomposition of the precursor compound in situ at temperatures as low as 110 A degrees C. The effects of the precursor concentration on the size of the CIS nanoparticles was studied by microstructure investigations (TEM, AFM, XRD) and UV-vis measurements show that these CIS composites possess a direct bandgap energy higher than 1.45 eV depending on the concentration of P3HT. PL quenching of P3HT polymer (i.e., higher accessible fraction of fluorophores) was found to be more for in situ rather than ex situ conditions for comparable CIX concentrations or particle size. This can be attributed to the fact that in in situ synthesis, P3HT act as surface directing template for CIS nanoparticles which is not so in the case of ex situ synthesis. Due to this, the polymeric stabilization of the CIS nanocomposites is better realized for in situ synthesis as compared to ex situ synthesis

Application of ZnO nanoparticles to enhance photoluminescence in porous silicon and its possible utilization for improving the short wavelength quantum efficiency of silicon solar cell

We have formed photoluminescent porous silicon (PS) layers and over which a ZnO layer (hereafter called ZnOPS layers) is deposited. We studied the photoluminescent properties of individual layers as well as the composite layer under excitation with 405 nm wavelength. Using the data of PL a theoretical analysis of a solar cell having such a composite layer of a given photoluminescent conversion efficiency eta(PL) on the front surface has been done. The condition of a photoluminescent composite layer (ZnOPS) useful for enhancing the spectral response of n(+)-p-p(+) structured silicon solar cell has been identified

Role of nanocrystalline ZnO coating on the stability of porous silicon formed on textured (1 0 0) Si

In this study, a colloid of nanocrystalline ZnO particles prepared by chemical route is sprayed on porous silicon layers. Porosity and thickness of PS layers were estimated by gravimetric analysis. Upon adsorption of ZnO colloids on PS films, oxidation of nanocrystalline Si causes shrinkage of the Si-core due to the breaking of Si Si bonds resulting in a blue-shift in PL spectra. The PL blue-shift can also be related to Si-0 species or due to defects and the silica networks on which OH groups are absorbed due to ZnO incorporation as also supported by our Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) studies, respectively. From high resolution X-ray diffraction (HRXRD) studies, a better crystalline perfection and considerable reduction in stress/strain values were observed for PS/ZnO layers as compared to virgin PS layers. The changes in the chemical composition at the surface of PS upon adsorption of ZnO colloids as elucidated by FTIR and XPS studies could be responsible for different PL emission and lattice-mismatch characteristics. The improved stability properties of PS are attributed to the strong absorption/adsorption of ZnO into the highly porous vertical layers separating macroscopic domains of nanoporous silicon and the mechanism of light emission from PS/ZnO layers is discussed on the basis of proposed energy band gap diagram