Microwave synthesis of CdSe and CdTe nanocrystals in nonabsorbing alkanes

Controlling nanomaterial growth via the "specific microwave effect" can be achieved by selective heating of the chalcogenide precursor. The high polarizability of the precursor allows instantaneous activation and subsequent nucleation leading to the synthesis of CdSe and CdTe in nonmicrowave absorbing alkane solvents. Regardless of the desired size, narrow dispersity nanocrystals can be isolated in less than 3 min with high quantum efficiencies and elliptical morphologies. The reaction does not require a high temperature injection step, and the alkane solvent can be easily removed. In addition, batch-to-batch variance in size is 4.2 +/- 0.14 nm for 10 repeat experimental runs. The use of a stopped-flow reactor allows near continuous automation of the process leading to potential industrial benefits.     

3D-ordered macroporous materials comprising DNA

Macroporous materials comprising DNA were fabricated with the colloidal crystal template. First, DNA and diazoresin (DR) molecules are fully filled into the voids of a colloidal crystal template. After thermal treatment and removal of the colloids, DNA porous materials with highly ordered structure were obtained. In the process of thermal treatment the cross-linking reaction takes place between DR and DNA, which plays an important role for sustaining the porous framework. The DNA porous materials will turn into a fluorescent DNA/dye composite after staining with Hoechst 33258 (Hoe), a characteristic fluorescent dye for DNA. This kind of composite DNA porous material may have potential applications in optical devices.     

Luminescence quenching in self-assembled adducts of [Ru(dpp)3]2+ complexes and CdTe nanocrystals

We have investigated chloroform solutions containing tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) and CdTe nanocrystal quantum dots (5.6 nm diameter). The electronic levels of these two components are such that the Ru complex can act as an energy donor towards the quantum dot, which can thus behave as an energy acceptor. Steady-state and time-resolved spectroscopic experiments indicate that the Ru complexes and the CdTe nanocrystals self-assemble to give stable 1?:?1 adducts, in which the luminescence of the former units is strongly quenched. Such a quenching can be ascribed to either energy transfer to the CdTe quantum dot, or to electron transfer from the CdTe valence band to the excited Ru complex. However, no supporting evidence for the occurrence of photoinduced energy transfer in the adduct could be found. The CdTe luminescence is also slightly quenched in the presence of the ruthenium complex. The strong association of the metal complexes with the nanocrystals suggests that self-assembly strategies may be effectively employed to achieve surface functionalization of semiconductor quantum dots with molecular units.     

Thiol-stabilized CdSe and CdTe nanocrystals in the size quantization regime: Synthesis,optical and structural properties

We report on the recently developed method for the synthesis, optical, and structural properties of CdSe and CdTe nanocrystals. They were formed in aqueous solutions at moderate temperatures by a wet chemical route in the presence of thiol molecules as effective stabilizing agents. The size-selective precipitation technique was applied for the post-preparative nanoparticle fractionation into a series of CdSe and CdTe nanocrystals with extremely narrow size distributions exhibiting mean cluster sizes in the range of 2 to 4 nm. The nature of stabilizing agent (mercaptoalcohols and mercaptoacids) had an important influence on the particle size and determines largely the photoluminescence properties. The nanocrystals were characterized by means of UV-vis absorption and photoluminescence spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy (HRTEM).     

Phosphine-free synthesis of CdSe nanocrystals

High quality CdSe nanocrystals have been prepared using elemental selenium as the chalcogenide precursor dispersed in 1-octadecene (ODE). The conditions used to prepare the Se precursor were found to be critical for successful nanocrystal synthesis. Systematic titration of the Se precursor solution with tri-n-octylphosphine (TOP) allowed the Se reactivity to be tuned and the final particle size to be controlled. Band-edge and surface related emission were observed for samples prepared in the presence and absence of added TOP. In the absence of a selenium passivant, the crystal structure of CdSe nanocrystals could be altered from zinc blende to wurtzite by the addition of bis(2,2,4-trimethylpentyl)phosphinic acid (TMPPA).     

Synthesis of CdSe/CdTe nanobarbells

Synthesis of monodisperse samples of CdSe nanorods with CdTe tips is achieved using the mechanism of rod nucleated growth to form CdSe/CdTe nanobarbells. This synthesis produces a nanocrystal displaying "type-II" behavior with a morphology that is particularly well suited for internal exciton separation and carrier transport.     

Binary superlattices of PbSe and CdSe nanocrystals

In this paper we show that self-organization of colloidal PbSe and CdSe semiconductor nanocrystals with a size ratio of 0.57 leads to binary structures with a AB2 or a cuboctahedral AB13 lattice. The type of superlattice formed can be regulated by the relative concentration of both nanocrystals in the suspension.     

Electrochemical properties of CdSe and CdTe quantum dots

Semiconductor nanocrystal quantum dots (QDs), owing to their unique opto-electronic properties determined by quantum confinement effects, have been the subject of extensive investigations in different areas of science and technology in the past two decades. The electrochemical behaviour of QDs, particularly for CdSe and CdTe nanocrystals, has also been explored, although to a lesser extent compared to the optical properties. Voltammetric measurements can be used to probe the redox levels available for the nanocrystals, which is an invaluable piece of information if these systems are involved in electron transfer processes. Electrochemical data can also foster the interpretation of the spectroscopic properties of QDs, and give insightful information on their chemical composition, dimension, and surface properties. Hence, electrochemical methods constitute in principle an effective tool to probe the quality of QD samples in terms of purity, size dispersion, and surface defects. The scope of this critical review is to discuss the results of electrochemical studies carried out on CdSe and CdTe core and core-shell semiconductor nanocrystals of spherical shape. Examples of emerging or potential applications that exploit electroactive quantum dot-based systems will also be illustrated.     

Single-nanocrystal spectroscopy of white-light-emitting CdSe nanocrystals

We report the observation of broad-spectrum fluorescence from single CdSe nanocrystals. Individual semiconductor nanocrystals typically have a narrower emission spectrum than that of an ensemble. However, our experiments show that the ensemble white-light emission observed in ultrasmall CdSe nanocrystals is the result of many single CdSe nanocrystals, each emitting over the entire visible spectrum. These results indicate that each white-light-emitting CdSe nanocrystal contains all the trap states that give rise to the observed white-light emission.     

Amine-assisted facetted etching of CdSe nanocrystals

The treatment of CdSe nanocrystals (NCs) in a 3-amino-1-propanol (APOL)/water (v/v = 10:1) mixture at 80 degrees C in the presence of O(2) causes them to undergo a slow chemical etching process, as evidenced by spectroscopic and structural investigations. Instead of the continuous blue shift expected from a gradual decrease in NC dimensions, a bottleneck behavior was observed with distinct plateaus in the peak position of photoluminescence (PL) and corresponding maxima in PL quantum yield (i.e., 34 +/-7%). It is presently argued that such etching behavior is a result of two competitive processes taking place on the surface of these CdSe NCs: (i) oxidation of the exposed Se-sites to acidic SeO(x)() entities, which are readily solubilized in the basic APOL/H(2)O mixture, and (ii) coordination of the underlying Cd-sites with both amines and hydroxyl moieties to temporally impede NC dissolution. This is consistent with the HRTEM results, which suggest that the etched NCs adopt pyramidal morphologies with Cd-terminated facets (i.e., (0001) bases and either {011} or {21} sides) and account for the apparent resistance to etching at the plateau regions.     

Water-soluble CdSe and CdSe/CdS nanocrystals: a greener synthetic route

We report a new green synthetic route of CdSe and core-shell CdSe/CdS nanoparticles (NPs) in aqueous solutions. This route is performed under water-bath temperature, using Se powder as a selenium source to prepare CdSe NPs, and H(2)S generated by the reaction of Na(2)SH(2)SO(4) as a sulfur source to synthesize core-shell CdSe/CdS NPs at 25-35 degrees C. The synthesis time of every step is only 20 min. After illumination with ambient natural light, photoluminescence (PL) intensities of CdSe NPs enhanced up to 100 times. The core-shell CdSe/CdS NPs have stronger photoactive luminescence with quantum yields over 20%. The obtained CdSe NPs exhibit a favorable narrow PL band (FWHM: 50-37 nm) with increasing molar ratio of Cd/Se from 4:1 to 10:1 at pH 9.1 in the crude solution, whereas PL band of corresponding CdSe/CdS NPs is slightly narrower. The emission maxima of nanocrystals can be tuned in a wider range from 492 to 592 nm in water by changing synthesis temperature of CdSe core than those reported previously. The resulting new route is of particular interest as it uses readily-available reagents and simple equipment to synthesize high-quality water-soluble CdSe and CdSe/CdS nanocrystals.     

Molecular assembly of a 3D-ordered multilayer

Combining strong metal-ligand coordination and pi-pi interactions affords a 3D-ordered molecular-based multilayer. The organization of the assembly is apparent from the optical properties and X-ray reflectivity.     

Preparation of CdSe nanocrystals in a micro-flow-reactor

A micro-reactor was utilized for continuous and controlled CdSe nanocrystal preparation. Effects of reaction conditions on optical properties of the nanocrystals were investigated; in this current system, rapid and exact temperature control of the micro-reactor was beneficial for controlling particle diameter and reproducible preparation of particles; additional effort was made towards narrower particle-size distributions.     

Oligothiophene-functionalized CdSe nanocrystals: preparation and electrochemical properties

The preparation of new molecular hybrids consisting of CdSe semiconductor nanocrystals, surface-functionalized with conductive and electrochemically active oligothiophene ligands, is described. Specially synthesized aniline-terminated oligoalkylthiophenes containing one, two, or four thiophene units were used for the grafting on CdSe nanocrystals, previously surface-functionalized with 4-formyldithiobenzoate. The electrochemical activity of both the inorganic and the organic parts of the hybrid was investigated by cyclic voltammetry. The oxidative doping of the organic part of the hybrid is irreversible, contrary to the case of the “free” non-grafted ligand which shows reversible doping. Furthermore, the electrochemical doping of the surface ligands, occurring at lower potentials than the oxidation of the nanocrystals, perturbs the latter process via charging of the ligands followed by slow relaxation processes. The first two authors contributed equally to this work Correspondence: Peter Reiss, Adam Pron, DSM/DRFMC/SPrAM (UMR 5819 CEA-CNRS-Université Joseph Fourier 1)/LEMOH CEA Grenoble, 17 rue des Martyrs, F-38054 Grenoble Cedex 9, France     

CdTe纳米晶与苯丙氨酸相互作用的研究

以巯基乙酸为稳定剂,在水相中合成了CdTe纳米晶,通过考察红外光谱、紫外光谱和光致发光光谱的变化,确定了苯丙氨酸(Phe)对CdTe纳米晶的光致发光效率以及稳定性的影响.结果表明苯丙氨酸与CdTe纳米晶之间存在着较强的相互作用,这种作用导致CdTe纳米晶的发光强度增大,稳定性增强,苯丙氨酸不仅是配位剂,它同时又起到了稳定剂的作用,并初步确认这种加强和稳定作用来自于苯丙氨酸和CdTe纳米晶之间所形成的配位键和静电作用以及苯丙氨酸与巯基乙酸之间形成的氢键.此外,苯丙氨酸的特殊结构对防止纳米晶的聚集有很大作用.     

CdTe nanocrystals sensitized chemiluminescence and the analytical application

It was found that the mixing of CdTe semiconductor nanocrystals (NCs) with luminol in the presence of KMnO₄ can induce a great sensitized effect on chemiluminescence (CL) emission. When the concentration of luminol, KMnO₄ and NaOH were fixed at 1 μM, 1 μM and 0.05 M, respectively, the most excellent performance can be obtained for the CdTe NCs sensitized CL. By means of CL and photoluminescence spectra, we suppose the enhanced CL signals resulted from the accelerated luminol CL induced by the oxidized species of CdTe NCs. Based on the finding, using thioglycolic acid-capped CdTe NCs as label and immunoglobulin G (IgG) as a model analyte, a CL immunoassay protocol for IgG content detection was developed. The strong inhibition effect of phenol compounds on luminol-KMnO₄-CdTe NCs CL system was also observed. All these findings demonstrated the possibility of semiconductor nanocrystals induced chemiluminescence to be utilized for more practical applications.     

PbSe/CdSe and PbSe/CdSe/ZnSe hierarchical nanocrystals and their photoluminescence

Multiple CdSe and ZnSe semiconductor shells were grown on PbSe semiconductor spherical cores with monolayer control. For CdSe shell coating, we found that there was little room to further increase the quantum yields of freshly-made high-quality PbSe nanocrystals that already owned very high initial values because of their good surface status; but there was great improvement for the PbSe nanocrystals with low initial quantum yields because of the poor surface status. Nonetheless, the quantum yield for the latter case could not reach the former's value. Additional ZnSe shells on PbSe/CdSe could further increase the quantum yield and protect the nanocrystals from air oxidation. The observed phenomena in the synthesis of the PbSe/CdSe and PbSe/CdSe/ZnSe core/shell structures were explained through the carrier wave function expansion and the surface polarization.     

Tin Domain Growth on Quasi-Two-Dimensional CdTe and CdSe Nanoparticles

Tin domain growth on quasi-two-dimensional colloidal CdSe and CdTe nanoparticles having the zinc blende structure has been studied. The initial quasi-two-dimensional CdSe and CdTe nanoparticles having lateral sizes of 100–200 nm were prepared by a colloidal method. Tin domain growth was accomplished in tetrahydrofuran via the reduction of a tin(II) salt by tetrabutylammonium borohydride. The tin domains had sizes of 10–20 nm as probed by TEM. In case of CdSe nanoparticles, tin domains were grown inside the inner cavities of initially rolled nanoparticles. A β-tin phase was identified by X-ray diffraction. The absorption spectra featured the broadening of exciton bands corresponding to quasi-two-dimensional nanoparticles, the spectral positions of absorption peaks remaining almost unchanged.