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Synthesis of CdSe/ZnS and CdTe/ZnS quantum dots

T1 - Aqueous synthesis of glutathione-capped CdTe/CdS/ZnS and CdTe/CdSe/ZnS core/shell/shell nanocrystal heterostructures

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Synthesis of CdSe/ZnS and CdTe/ZnS quantum dots: ..

A method for the labelling of CdSe/CdS/ZnS QDs during the synthesis process with radioactive 65Zn in one of the outer shells of the nanoparticles has been developed. The challenges associated with the handling of radioactive materials and the minimization of the synthesis in order to avoid excessive generation of radioactive waste have been resolved. To this effect, a procedure strategy was designed where the main advantage is a high degree of operator safety and the avoidance of direct hand contact with the radioactive materials. Further, by varying the amounts of 65ZnCl2 and ZnCl2, the radioactivity per particle can be controlled. Interestingly, we observed a 65ZnS shell formation which was thinner than expected the thickness, resulting in a lower 65Zn incorporation, the exact origin of which is currently under investigation.

 47. Mokari T, Banin U. Synthesis and Properties of CdSe/ZnS Core/Shell Nanorods.  2003;15:3955-60

Figure 1. Absorbance and photoluminescence spectra for CdSe and CdSe/ZnS core/shell NPLs. Bottom (full lines): Spectra of the original CdSe core NPLs (sample 1). Middle (full lines): Spectra of CdSe/ZnS NPLs that are synthesized from a zinc oleyl-carbamic precursor produced in situ. The PL QE (λex = 390 nm) equals 13%. Top (dashed lines): Spectra of CdSe/ZnS NPLs, with a ZnS shell obtained with Zn(DDTC)2. The PL QE has increased to 30%. Inset: Photo image of CdSe NPLs (left) and CdSe/ZnS core/shell NPLs (right, synthesized with Zn(DDTC)2), both suspended in hexane under 365 nm UV illumination.

11/11/2015 · Synthesis of ZnS, CdS and Core ..

T1 - High temperature continuous flow synthesis of CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS nanocrystals

Here we demonstrate the aqueous synthesis of colloidal nanocrystal heterostructures consisting of the CdTe core encapsulated by CdS/ZnS or CdSe/ZnS shells using glutathione (GSH), a tripeptide, as the capping ligand. The inner CdTe/CdS and CdTe/CdSe heterostructures have type-I, quasi-type-II, or type-II band offsets depending on the core size and shell thickness, and the outer CdS/ZnS and CdSe/ZnS structures have type-I band offsets. The emission maxima of the assembled heterostructures were found to be dependent on the CdTe core size, with a wider range of spectral tunability observed for the smaller cores. Because of encapsulation effects, the formation of successive shells resulted in a considerable increase in the photoluminescence quantum yield; however, identifying optimal shell thicknesses was required to achieve the maximum quantum yield. Photoluminescence lifetime measurements revealed that the decrease in the quantum yield of thick-shell nanocrystals was caused by a substantial decrease in the radiative rate constant. By tuning the diameter of the core and the thickness of each shell, a broad range of high quantum yield (up to 45%) nanocrystal heterostructures with emission ranging from visible to NIR wavelengths (500-730 nm) were obtained. This versatile route to engineering the optical properties of nanocrystal heterostructures will provide new opportunities for applications in bioimaging and biolabeling.

N2 - Here we demonstrate the aqueous synthesis of colloidal nanocrystal heterostructures consisting of the CdTe core encapsulated by CdS/ZnS or CdSe/ZnS shells using glutathione (GSH), a tripeptide, as the capping ligand. The inner CdTe/CdS and CdTe/CdSe heterostructures have type-I, quasi-type-II, or type-II band offsets depending on the core size and shell thickness, and the outer CdS/ZnS and CdSe/ZnS structures have type-I band offsets. The emission maxima of the assembled heterostructures were found to be dependent on the CdTe core size, with a wider range of spectral tunability observed for the smaller cores. Because of encapsulation effects, the formation of successive shells resulted in a considerable increase in the photoluminescence quantum yield; however, identifying optimal shell thicknesses was required to achieve the maximum quantum yield. Photoluminescence lifetime measurements revealed that the decrease in the quantum yield of thick-shell nanocrystals was caused by a substantial decrease in the radiative rate constant. By tuning the diameter of the core and the thickness of each shell, a broad range of high quantum yield (up to 45%) nanocrystal heterostructures with emission ranging from visible to NIR wavelengths (500-730 nm) were obtained. This versatile route to engineering the optical properties of nanocrystal heterostructures will provide new opportunities for applications in bioimaging and biolabeling.

Aqueous synthesis of glutathione-capped CdTe/CdS/ZnS …

(CdSe)ZnS core-shell quantum dots: synthesis and characterization of a …

N2 - Here we demonstrate the aqueous synthesis of colloidal nanocrystal heterostructures consisting of the CdTe core encapsulated by CdS/ZnS or CdSe/ZnS shells using glutathione (GSH), a tripeptide, as the capping ligand. The inner CdTe/CdS and CdTe/CdSe heterostructures have type-I, quasi-type-II, or type-II band offsets depending on the core size and shell thickness, and the outer CdS/ZnS and CdSe/ZnS structures have type-I band offsets. The emission maxima of the assembled heterostructures were found to be dependent on the CdTe core size, with a wider range of spectral tunability observed for the smaller cores. Because of encapsulation effects, the formation of successive shells resulted in a considerable increase in the photoluminescence quantum yield; however, identifying optimal shell thicknesses was required to achieve the maximum quantum yield. Photoluminescence lifetime measurements revealed that the decrease in the quantum yield of thick-shell nanocrystals was caused by a substantial decrease in the radiative rate constant. By tuning the diameter of the core and the thickness of each shell, a broad range of high quantum yield (up to 45%) nanocrystal heterostructures with emission ranging from visible to NIR wavelengths (500-730 nm) were obtained. This versatile route to engineering the optical properties of nanocrystal heterostructures will provide new opportunities for applications in bioimaging and biolabeling.

Continuous flow reactors show great promise for large-scale synthesis of quantum dots. Here, we discuss results for the synthesis of multi-layered Cd-based hybrid nanocrystals-CdSe/CdS/ZnS, CdS/ZnS, and CdSeS/ZnS-in a continuous flow reactor. The simple reactor design and liquid-phase chemistry obviate the need for preheating or in-line mixing, and the chosen reactor dimensions and operating conditions allow for high flow rates (∼10 mL min-1). Additionally, the simple reactor design is well suited for scale-up. The CdSe/CdS/ZnS particles synthesized at elevated temperatures in the reactor exhibit quantum yields of over 60% at longer wavelengths (red region). The shell growth for these particles is conducted without the need for complex dropwise addition or SILAR shell growth procedures used in batch reactors. CdS-based particles were shown to have a higher performance when using octadecene-S instead of TOP-S, which improved the quality of shell growth. In addition, stoichiometric synthesis of the alternate CdSeS/ZnS alloy particles was conducted, removing the need for a large excess of S to offset the lower S reactivity. CdSeS/ZnS alloy nanoparticles exhibit quantum yields of about 50% in the intermediate wavelength range (500-600 nm).

CdTe and CdSe quantum dots: synthesis, …
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  • Synthesis of radioactively labelled CdSe/CdS/ZnS …

    (ZnS, CdS, CdSe, ..

  • CdSe ZnS Core-Shell Quantum Dots Synthesis and ..

    Synthesis of CdSe/ZnS Core ..

  • Synthesis of Air-Stable CdSe/ZnS Core–Shell …

    Aqueous synthesis of glutathione-capped CdTe/CdS/ZnS and CdTe/CdSe/ZnS core/shell/shell nanocrystal heterostructures

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Synthesis of Extremely Small CdSe and Highly …

A red shift in the absorbance and PL spectra indicates the formation of a CdS shell surrounding the CdSe QDs (). During the formation of the non-radioactive ZnS shell, a slight blue shift and a weakening of the absorbance was observed. Due to the radioactivity and safety issues, spectra could not be taken for the CdSe/CdS/65ZnS/ZnS QDs. However, the PL of both the cleaned CdSe/CdS/ZnS and the CdSe/CdS/65ZnS/ZnS QDs show no significant difference under UV illumination () with the PL remaining unchanged even after one month. The radiation due to the 65Zn decay does not appear to influence the PL intensity to any great extent.

Synthesis and Optical Properties of CdSe and CdSe/ZnS …

For the synthesis of radioactively labelled material, it was necessary to significantly alter the coating process from the routine SILAR protocol. The main challenges were to use 65ZnCl2 as the radioactive zinc precursor instead of the commonly used ZnO or Zn(oleate)2 in the SILAR synthetic routes and to reduce the contact time involved in the handling of the radioactive material as much as possible. For this purpose, 65ZnCl2 diluted in 0.1 M HCl(aq) was placed in an empty, lead glass shielded flask where it was converted to a species more useful for the labelling of CdSe/CdS QDs by the in situ formation of zinc stearate (65Zn(stearate)2). After addition of the previously prepared QD materials and adsorption of 65Zn2+ onto the QD surface, the sulphur precursor was added to the flask to form a shell of 65ZnS. To avoid later desorption of radioactive 65Zn2+ ions from the surface, another ZnS shell (using a nonradioactive zinc precursor) was applied to the QDs using the typical SILAR procedure () [,]. The main advantage of this method is that the radioactive material can be added at ambient temperature and shielded by lead glass using a pipette, which prevents direct hand contact from the very beginning. All other materials may be added safely from a sufficient distance and behind lead glass.

A simple and facile synthesis of MPA capped CdSe and CdSe/CdS core ..

In light of the above considerations, down-scaling entails the design of a completely new synthesis route which includes the optimization of the typical synthesis parameters such as batch size, relative concentrations, injection and ripening temperatures, etc. By contrast, due to the extremely small volumes and masses involved, the down-scaling is limited by the degree of control over the stirring rates and temperature. A judicious modification of the protocol with respect to the ratio of reactants, ligands and solvents allows the synthesis procedure to be scaled down to amounts of CdSe/CdS QDs on the order of 5 nmol.

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