Adsorption and binding of capping molecules for highly luminescent CdSe nanocrystals--DFT simulation studies

During CdSe nanocrystal growth, loss of surface capping molecules occurs leading to a decrease of photoluminescence (PL) quantum yield. In general, aliphatic capping molecules are applied to passivate the surface of CdSe nanocrystals to modulate the optical properties of the CdSe. In this work, two kinds of alkylamine (n-butylamine (n-BA) and n-hexylamine (n-HA)) and oleic acid (OA) were used to modify the surfaces of the CdSe nanocrystals. From the PL spectra and quantum yield analyses, we observed that the PL emission peak positions of the modified CdSe nanocrystals have blue shifted for all three capping molecules. However, the PL quantum yield of the CdSe nanocrystals increased after introduction of the alkylamine molecules, but decreased with oleic acid. The detailed mechanism was not clear until now. In this study, a density function theory (DFT) simulation was employed to demonstrate binding energy and charge analyses of CdSe with n-BA, n-HA and OA. By comparing the binding energy of the bare CdSe nanocrystals to that of the CdSe with the capping molecules, it was shown that n-BA and n-HA as capping molecules help to increase the charge on Se and decrease it on cadmium of the CdSe.     

CdSe@ZnSe@SiO2核壳壳型纳米粒子的制备与表征

通过TOP-TOPO-HDA路线制备了CdSe纳米晶体,并在此基础上通过一步法制备出CdSe@ZnSe核壳纳米粒子。利用环己烷-壬基酚聚（5）氧乙烯醚（NP-5）-水的微乳体系为模板,通过硅烷偶联剂的作用制备出CdSe@ZnSe@SiO2复合纳米粒子,并通过TEM、EDX和UV-Vis等手段对所得纳米粒子进行了表征。     

Formation of PbSe/CdSe Core/Shell Nanocrystals for Stable Near-Infrared High Photoluminescence Emission

PbSe/CdSe core/shell nanocrystals with quantum yield of 70% were obtained by the “successive ion layer adsorption and reaction” technology in solution. The thickness of the CdSe shell was exactly controlled. A series of spectral red shifts with the CdSe shell growth were observed, which was attributed to the combined effect of the surface polarization and the expansion of carriers’ wavefunctions. The stability of PbSe nanocrystals was tremendously improved with CdSe shells.     

The growth of CdSe quantum dots on a single wall carbon nanotubes template without organic solvent and surfactant

A conventional synthesis of Cadmium selenide (CdSe) quantum dots (QDs) usually employs toxic organic solvents, and the synthesized CdSe QDs must be modified for dispersion in an aqueous solution. This modification often limits the application of CdSe QDs in biomedical fields. In this study, a simple method was developed to synthesize CdSe QDs on single wall carbon nanotubes (SWCNTs) employing the SWCNTs as a template to prevent the aggregation of the CdSe QDs in an aqueous solution without the addition of any organic reagent.Our newly developed synthetic procedure included the formation of SWCNTs with carboxyl groups (SWCNT-COOHs) followed by mixing these with the precursors of Cd and Se to obtain SWCNT-CdSe QDs. The resulting SWCNT-CdSe QDs were analyzed using spectrophotometry, transmission electron microscopy (TEM) and X-ray diffraction (XRD).Results showed that CdSe nanocrystals with a zinc blend structure could be synthesized on the SWCNT-COOHs. The average crystal size of the synthesized CdSe QDs was approximately 3 nm. The blue-shift of CdSe QDs powerfully emitted light at 550 nm as compared to the bulk CdSe at 730 nm. These CdSe QDs were synthesized in an aqueous environment without using toxic surfactants and are expected to have great potential as bio-labeling contrast agents in the future.     

CdS/CdSe核壳结构半导体纳米晶结构及光谱特性

采用共沉淀法在水相中将CdS外延生长于CdSe半导体纳米晶(CdSe NCs)表面,制备了结晶形态较好的CdSc/CdS核壳结构半导体纳米晶(CdSe/CdS C/S NCs),并改善了CdSe NCs的荧光性能.通过X射线衍射,透射电镜和选区电子衍射分析证明了核壳结构的形成,并通过紫外可见光吸收光谱和荧光光谱分析证明了核壳结构对CdSe NCs荧光性能的改善.此外,实验结果表明:控制CdSe核合成中Cd前驱体溶液pH值能获得粒径分布较窄的CdSe/CdS C/S NCs;采用不同浓度比的Cd和Se前驱体溶液可以有效调节核壳结构半导体纳米晶的粒径;选择合适的CdSe与CdS摩尔比及壳层中Cd与S摩尔比能改善CdSe/CdS C/S NCs的荧光性能.     

Size-Quantized Nanocrystalline Semiconductor Films

This paper is a review of our work on nanocrystalline semiconductor films which exhibit pronounced size quantization effects in three dimensions, manifested by large blue-shifts in their optical absorption spectra. The films are prepared by either chemical solution deposition (CdSe and PbSe) or by electrodeposition from nonaqueous electrolytes (CdSe and CdS). Except for PbSe, where the nanocrystals are surrounded by a matrix, the films are comprised of aggregated nanocrystals. Crystal size (typically from <4 nm to >6 nm), and therefore absorption spectra, can be controlled by deposition temperature, illumination during deposition (for chemically deposited films), solution composition, and post annealing. The crystal size dependence of chemically-deposited films on experimental parameters (temperature, illumination, reactant concentrations) is discussed. CdSe nanocrystals were epitaxially electrodeposited on single-crystal Au. The nanocrystal distribution (isolated or aggregated) could be controlled by deposition current and temperature. All these films exhibit photoelectrochemical behavior but no corresponding solid state photovoltaic behavior. A model is proposed based on electron/hole separation by kinetic differences in charge injection into an electrolyte rather than by a built-in space charge layer in the semiconductor. The films can behave as both ‘n’ - or ‘p’-type, with respect to direction of photocurrent flow, by changes in the semiconductor surface properties and/or the electrolyte, in agreement with this model.     

Arm length dependency of Pt-decorated CdSe tetrapods on the performance of photocatalytic hydrogen generation

Pt-decorated CdSe tetrapods with different arm lengths were tested for the photocatalytic hydrogen generation reaction. Well-defined CdSe tetrapods with controlled wurtzite arm lengths were synthesized by the continuous precursor injection (CPI) approach. Pt nanocrystals with an extremely small size of ～1 nm were directly decorated on the overall surfaces of CdSe tetrapods. Ligand-exchanged Pt-decorated CdSe tetrapods with different arm lengths were employed as photocatalysts for photocatalytic hydrogen generation reaction in the presence of hole scavengers. Pt-decorated CdSe tetrapods with shorter arm length showed the highest photocatalytic efficiency, which is due to higher probability of charge separation.     

CdSe nanocrystal sensitized ZnO core-shell nanorod array films: Preparation and photovoltaic properties

ZnO/CdSe core-shell nanorod array films were synthesized via a two-step method. ZnO nanorod array films were first grown on a TCO substrate, and then CdSe nanocrystals were deposited on the nanorods to form core-shell structured films. The resulting films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis absorption spectroscopy. Especially, dark-field images and transmission electron diffraction of the TEM were used to study the morphology and the chemical nanostructure of the ZnO/CdSe core-shell nanorods in detail. We investigated the photovoltaic performance of the resulting ZnO/CdSe core-shell nanorod array films as solar cell photoanodes. Parameters, such as the length of the ZnO nanorods, the shell phase structure and the deposition time of the CdSe nanocrystals were found to affect the photovoltaic performance of the solar cell. This study provides a facile method to prepare nanocomposite photoanodes of solar cells, and gives some insight about the fundamental mechanisms that improve the performance.     

CdSe Ring- and Tribulus-Shaped Nanocrystals: Controlled Synthesis, Growth Mechanism, and Photoluminescence Properties

With air-stable and generic reagents, CdSe nanocrystals with tunable morphologies were prepared by controlling the temperature in the solution reaction route. Thereinto, the lower reaction temperature facilitates the anisotropic growth of crystals to obtain high-yield CdSe ring- and tribulus-shaped nanocrystals with many branches on their surfaces. The photoluminescence properties are sensitive to the nature of particle and its surface. The products synthesized at room temperature, whose surfaces have many branches, show higher blue shift and narrower emission linewidths (FWHM) of photoluminescence than that of samples prepared at higher temperature, whose surfaces have no branches. Microstructural studies revealed that the products formed through self-assembly of primary crystallites. Nanorings formed through the nonlinear attachment of primary crystallites, and the branches on the surfaces grew by linear attachment at room temperature. And the structure of tribulus-shaped nanoparticle was realized via two steps of aggregation, i.e., random and linear oriented aggregation. Along with the elevation of temperature, the branches on nanocrystal surfaces shortened gradually because of the weakened linear attachment. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phosphate ester side‐chain‐modified conjugated polymer for hybrid solar cells

Although nanocrystals have several advantages of tunable bandgap and high carrier mobility, it is still challenging to achieve high‐performance polymer: nanocrystals hybrid solar cells (HSC) due to the complicated surface problem. Many efforts have been devoted to replace the long alkyl chain on the surface of nanocrystals to improve the charge transfer and transport. Herein, we modified the alkyl chain in poly[2,6–(4,4‐bis (2‐ethylhexyl)?4H‐cyclopenta[2,1‐b;3,4‐b′]‐dithiophene)‐alt ‐4,7–(2,1,3‐benzothiadiazole)] (PCPDTBT) by phosphate ester. Due to its strong affinity to CdSe nanocrystals, the resulting polymers can spontaneously exchange the long chain ligands in one‐step process. With the improved morphology of polymer: CdSe blended film, a power conversion efficiency (PCE) of 3.12% was achieved for hybrid solar cells. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45003.     

水热法制备细胞标记用CdSe半导体量子点材料

介绍了水热合成CdSe半导体纳米晶的工艺,调节反应温度及时间有助于加速CdSe纳米晶的生长,使其荧光产率得到显著提高;在一定的初始条件下,随着纳米晶核长大,产物的荧光产率单调增至极值然后逐渐下降;CdSe荧光产率的最大值与反应温度关系密切。实验利用1-乙基–1-3-(3-二甲基氨基-丙基)–碳化二亚胺将所制备的CdSe与转铁蛋白偶联成生物探针,成功标记了人肺腺癌细胞。     

用环己烷-水两相体系优化合成CdSe量子点

采用环己烷和水组成的两相体系,合成了不同粒径大小的硒化镉量子点。用X射线粉末衍射仪（XRD）,透射电子显微镜（TEM）,荧光光谱仪和紫外可见分光光度计等测试手段对产物进行了表征,结果表明生成的量子点粒径尺寸分布均匀,为立方晶型,具有良好的荧光特性。讨论了反应物比例、反应温度、反应时间、硒单体的量等因素对CdSe量子点的粒径分布,表面缺陷,奥斯德瓦尔效应的影响。通过优化实验条件,得到了表面缺陷少,粒径分布均匀,光量子效率高的硒化镉量子点。     

High yield synthesis of matchstick-like PbS nanocrystals using mesoporous organosilica as template

A simple hard template method has been developed to prepare uniform matchstick-like PbS nanocrystals. The approach combines functionalization of the mesoporous walls and channel surface with thioether groups, adsorption of Pb2+, and heating in an N2 atmosphere at high temperature. The structure, morphology and composition of the nanocrystals have been characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The optical properties of the matchstick-like PbS nanocrystals have been systematically investigated by Raman spectroscopy, UV-visible absorption spectroscopy (UV-vis), and photoluminescence spectroscopy (PL). These results demonstrate that these matchstick-like PbS nanocrystals are single crystals and possess novel optical properties, suggesting that they may have many potential applications. A large blue shift is observed in the photoluminescence spectrum, and this clearly shows the quantum size effects of the matchstick-like PbS . Furthermore, a growth mechanism of the PbS heteronanostructure is proposed.     

Study on third-order optical nonlinear properties of transparent chalcogenide glass ceramics within Ge–S binary system

transparent chalcogenide glass ceramics (ChGCs) based on a binary germanium-sulfur (Ge–S, GS) chalcogenide system were synthesized by heat treatment method. Compared with the precursor glass, the GS ChGCs embedded with GeS₂ nanocrystals have the same infrared transparency, but smaller optical bandgap energy and higher mechanical strength. Z-scan measurements show that third-order optical nonlinearity in the GS ChGCs was remarkably enhanced, and this material would be suitable for applications in optical limiting.     

谷氨酰胺为稳定剂制备硒化镉纳米晶及光谱性质研究

以谷氨酰胺(Gln)为稳定剂合成了硒化镉纳米晶,利用X-射线粉末衍射(XRD)和透射电镜(TEM)对纳米晶结构进行了表征,粒径约为20 nm。通过紫外-可见吸收光谱、激发光谱与发射光谱研究了纳米晶光谱特性。实验结果表明,反应温度过高、反应时间过长都会破坏谷氨酰胺(Gln)的稳定作用,使CdSe聚集,影响其荧光性质。而聚乙二醇(PEG)的加入会使纳米晶的荧光发射明显加强,而且发射峰峰形尖锐。     

Synthesis and Characterization of Cadmium Selenide Nanorods Via Surfactant-Assisted Hydrothermal Method

Single-crystal CdSe nanorods ([001] orientation) with diameters in the range of 40–60 nm and aspect ratios of 5–8 were successfully synthesized at 180°C for 10 h through a facile surfactant-assisted hydrothermal method, using Na₂SeO₃ as a high-quality soluble selenium source. The products were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and ultraviolet–vis spectra analysis. It was found that the surfactant (cetyltrimethyl ammonium bromide) played a vital role in the process. Through varying the concentrations of surfactant, the morphologies changed from dendrite-like nanostructure to nanorods, short nanorods, and nanoparticles. The possible mechanism for the growth of CdSe nanocrystals was also discussed.     

Controlling the morphology of trioctyl phosphine oxide-coated cadmium selenide/poly 3-hexyl thiophene composite active layer for bulk hetero-junction solar cells

Bulk hetero-junction solar cells with CdSe nanoparticles-P₃HT (poly 3-hexyl thiophene) composite active layer were fabricated, and the control of morphological feature of the nanoparticle-polymer composite thin films was investigated. A binary solvent composed of a primary solvent with intermediate polarity and a secondary solvent with high polarity was found to be effective in controlling the dispersion of the CdSe nanocrystals in the P₃HT matrix, and the modification of the nanocrystal surface by liquid-liquid extraction process was found to be effective in achieving the desired composite film morphology. Surface roughness of the active layer was optimized for various loadings of CdSe nanoparticles and could be reproducibly controlled to less than 10 nm.     

Low temperature solution-phase growth of ZnSe and ZnSe/CdSe core/shell nanowires

High quality ZnSe nanowires (NWs) and complementary ZnSe/CdSe core/shell species have been synthesized using a recently developed solution-liquid-solid (SLS) growth technique. In particular, bismuth salts as opposed to pre-synthesized Bi or Au/Bi nanoparticles have been used to grow NWs at low temperatures in solution. Resulting wires are characterized using transmission electron microscopy and possess mean ensemble diameters between 15 and 28 nm with accompanying lengths ranging from 4-10 μm. Subsequent solution-based overcoating chemistry results in ZnSe wires covered with CdSe nanocrystals. By varying the shell's growth time, different thicknesses can be obtained and range from 8 to 21 nm. More interestingly, the mean constituent CdSe nanocrystal diameter can be varied and results in size-dependent shell emission spectra.     

自牺牲模板法制备CdSe负载的CdS纳米线及其表征

以六方相CdS纳米线为前驱物,在不同浓度的Na2SeSO3水溶液中,采用水热合成法制备了负载量可控的CdSe沉积的CdS纳米线复合材料。采用XRD、SEM、TEM、UV-vis、PL和FTIR对该复合材料的物相、组成、形貌及光学性能进行了详细表征。结果表明,CdSe呈纤锌矿型六方相结构的纳米层形态沉积在CdS表面,其负载量受Na2SeSO3水溶液浓度、反应温度和反应时间控制;与CdS纳米线相比,纳米复合材料的可见光吸收范围明显扩大,覆盖了可见光的大部分区域,而其中的CdS纳米线荧光因CdSe的存在出现猝灭现象,同样,也未观察到CdSe的荧光。该文详细讨论了相关的光学性质以及纳米复合物的反应机理。     

Surface and spectroscopic properties of CdSe/ZnS/PVC nanocomposites

It is valuable to understand the way the wettability is affected by the solid and the liquid surface free energies. For this study, transparent films of CdSe/ZnS/PVC nanocomposites have been prepared and characterized by FTIR and contact angle measurements. Moreover, the presence of polar interactions at the liquid/polymer interfaces, which show a proportionality to the polar components of the liquid surface energy for pure polyvinyl chloride (PVC) and all CdSe/ZnS/PVC nanocomposites, is also studied. By using the surface polarizability hypothesis, there is possibility to obtain the dispersion component of surface‐free energies of pure PVC and also its nanocomposites from the contact angles measurement of only polar liquids. This approximately is coincident with that published data for pure PVC obtained from both polar and nonpolar liquids' contact angles. In addition to this, the absorption spectra and the photoluminescence illustrate clearly the effect of CdSe/ZnS quantum dots on their host matrix. The calculated values of the optical parameters, such as energy gap and Urbach energy, illustrate an inverse proportionality between them. POLYM. COMPOS., 38:749–758, 2017. © 2015 Society of Plastics Engineers