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Rational design of the gram-scale synthesis of nearly monodisperse semiconductor nanocrystals.

Protière M, Nerambourg N, Renard O, Reiss P - Nanoscale Res Lett (2011)

Bottom Line: On the basis of these results, the synthesis has been scaled up by a factor of 20.Using a 2-L batch reactor combined with a high-throughput peristaltic pump, different-sized samples of CdSe nanocrystals with yields of 2-3 g per synthesis have been produced without sacrificing the narrow size distribution.In a similar setup, the gram-scale synthesis of CdSe/CdS/ZnS core/shell/shell nanocrystals exhibiting a fluorescence quantum yield of 81% and excellent resistance of the photoluminescence in presence of a fluorescent quencher (aromatic thiol) has been achieved.PACS: 81.20.Ka, 81.07.Bc, 78.67.Bf.

View Article: PubMed Central - HTML - PubMed

Affiliation: DSM/INAC/SPrAM (UMR 5819 CEA-CNRS-UJF)/LEMOH, CEA-Grenoble - 17 rue des Martyrs - 38054 Grenoble cedex 9, France. peter.reiss@cea.fr.

ABSTRACT
We address two aspects of general interest for the chemical synthesis of colloidal semiconductor nanocrystals: (1) the rational design of the synthesis protocol aiming at the optimization of the reaction parameters in a minimum number of experiments; (2) the transfer of the procedure to the gram scale, while maintaining a low size distribution and maximizing the reaction yield. Concerning the first point, the design-of-experiment (DOE) method has been applied to the synthesis of colloidal CdSe nanocrystals. We demonstrate that 16 experiments, analyzed by means of a Taguchi L16 table, are sufficient to optimize the reaction parameters for controlling the mean size of the nanocrystals in a large range while keeping the size distribution narrow (5-10%). The DOE method strongly reduces the number of experiments necessary for the optimization as compared to trial-and-error approaches. Furthermore, the Taguchi table analysis reveals the degree of influence of each reaction parameter investigated (e.g., the nature and concentration of reagents, the solvent, the reaction temperature) and indicates the interactions between them. On the basis of these results, the synthesis has been scaled up by a factor of 20. Using a 2-L batch reactor combined with a high-throughput peristaltic pump, different-sized samples of CdSe nanocrystals with yields of 2-3 g per synthesis have been produced without sacrificing the narrow size distribution. In a similar setup, the gram-scale synthesis of CdSe/CdS/ZnS core/shell/shell nanocrystals exhibiting a fluorescence quantum yield of 81% and excellent resistance of the photoluminescence in presence of a fluorescent quencher (aromatic thiol) has been achieved.PACS: 81.20.Ka, 81.07.Bc, 78.67.Bf.

No MeSH data available.


TEM images, UV-vis absorption spectra, and PL spectra of core and core/shell/shell nanocrystals. TEM images of 4-nm CdSe core (a) and of the corresponding 6.2-nm CdSe/CdS/ZnS core/shell/shell nanocrystals (b) at the same magnification; (c) at higher magnification. d) UV-vis absorption spectra (the spectrum of the core/shell/shell nanocrystals has been shifted vertically for clarity); e) PL spectra (excitation wavelength, 400 nm) of the core and core/shell/shell nanocrystals.
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Figure 4: TEM images, UV-vis absorption spectra, and PL spectra of core and core/shell/shell nanocrystals. TEM images of 4-nm CdSe core (a) and of the corresponding 6.2-nm CdSe/CdS/ZnS core/shell/shell nanocrystals (b) at the same magnification; (c) at higher magnification. d) UV-vis absorption spectra (the spectrum of the core/shell/shell nanocrystals has been shifted vertically for clarity); e) PL spectra (excitation wavelength, 400 nm) of the core and core/shell/shell nanocrystals.

Mentions: In order to improve the stability against photobleaching and the quantum yield of the obtained CdSe nanocrystals, their surface was subsequently passivated with a CdS/ZnS double shell. The intermediate CdS shell serves as "lattice mismatch mediator", reducing the strain between the CdSe core and the ZnS outer shell [36,37]. The same reactor was used as in the core nanocrystal synthesis, while a syringe pump replaced the peristaltic pump for the slow injection of the shell precursors. The latter were composed of a mixture of cadmium ethylxanthate and cadmium stearate for the CdS shell and of zinc ethylxanthate/zinc stearate for the ZnS shell, respectively [26]. During the shell growth, a red shift of the absorption (from 556 to 582 nm) and PL (from 573 to 592 nm) peaks is observed, indicating the partial delocalization of the exciton in the shell (Figure 4d or 4e). The PL FWHM increases from 32 to 37 nm during the shell growth, going along with the enlargement of the size dispersion from 7.5% to 10%. The fluorescence quantum yield (QY) of the obtained CdSe/CdS/ZnS nanocrystals accounts for 81%, i.e., shell growth led to an increase of the PL QY by a factor of 10. In contrast to the used rather spherical CdSe core nanocrystals, the core/shell/shell particles have a more facetted shape. On TEM images (Figure 4a, b, c), a size difference of 2.2 nm between the core and core/shell/shell nanocrystals has been determined corresponding to three to four shell monolayers. This size increase is expected in view of the quantity of the injected shell precursors (calculated for obtaining 1.3 CdS monolayers and 2.5 ZnS monolayers), indicating that essentially the whole amount of precursors has been deposited on the core nanocrystals.


Rational design of the gram-scale synthesis of nearly monodisperse semiconductor nanocrystals.

Protière M, Nerambourg N, Renard O, Reiss P - Nanoscale Res Lett (2011)

TEM images, UV-vis absorption spectra, and PL spectra of core and core/shell/shell nanocrystals. TEM images of 4-nm CdSe core (a) and of the corresponding 6.2-nm CdSe/CdS/ZnS core/shell/shell nanocrystals (b) at the same magnification; (c) at higher magnification. d) UV-vis absorption spectra (the spectrum of the core/shell/shell nanocrystals has been shifted vertically for clarity); e) PL spectra (excitation wavelength, 400 nm) of the core and core/shell/shell nanocrystals.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3211985&req=5

Figure 4: TEM images, UV-vis absorption spectra, and PL spectra of core and core/shell/shell nanocrystals. TEM images of 4-nm CdSe core (a) and of the corresponding 6.2-nm CdSe/CdS/ZnS core/shell/shell nanocrystals (b) at the same magnification; (c) at higher magnification. d) UV-vis absorption spectra (the spectrum of the core/shell/shell nanocrystals has been shifted vertically for clarity); e) PL spectra (excitation wavelength, 400 nm) of the core and core/shell/shell nanocrystals.
Mentions: In order to improve the stability against photobleaching and the quantum yield of the obtained CdSe nanocrystals, their surface was subsequently passivated with a CdS/ZnS double shell. The intermediate CdS shell serves as "lattice mismatch mediator", reducing the strain between the CdSe core and the ZnS outer shell [36,37]. The same reactor was used as in the core nanocrystal synthesis, while a syringe pump replaced the peristaltic pump for the slow injection of the shell precursors. The latter were composed of a mixture of cadmium ethylxanthate and cadmium stearate for the CdS shell and of zinc ethylxanthate/zinc stearate for the ZnS shell, respectively [26]. During the shell growth, a red shift of the absorption (from 556 to 582 nm) and PL (from 573 to 592 nm) peaks is observed, indicating the partial delocalization of the exciton in the shell (Figure 4d or 4e). The PL FWHM increases from 32 to 37 nm during the shell growth, going along with the enlargement of the size dispersion from 7.5% to 10%. The fluorescence quantum yield (QY) of the obtained CdSe/CdS/ZnS nanocrystals accounts for 81%, i.e., shell growth led to an increase of the PL QY by a factor of 10. In contrast to the used rather spherical CdSe core nanocrystals, the core/shell/shell particles have a more facetted shape. On TEM images (Figure 4a, b, c), a size difference of 2.2 nm between the core and core/shell/shell nanocrystals has been determined corresponding to three to four shell monolayers. This size increase is expected in view of the quantity of the injected shell precursors (calculated for obtaining 1.3 CdS monolayers and 2.5 ZnS monolayers), indicating that essentially the whole amount of precursors has been deposited on the core nanocrystals.

Bottom Line: On the basis of these results, the synthesis has been scaled up by a factor of 20.Using a 2-L batch reactor combined with a high-throughput peristaltic pump, different-sized samples of CdSe nanocrystals with yields of 2-3 g per synthesis have been produced without sacrificing the narrow size distribution.In a similar setup, the gram-scale synthesis of CdSe/CdS/ZnS core/shell/shell nanocrystals exhibiting a fluorescence quantum yield of 81% and excellent resistance of the photoluminescence in presence of a fluorescent quencher (aromatic thiol) has been achieved.PACS: 81.20.Ka, 81.07.Bc, 78.67.Bf.

View Article: PubMed Central - HTML - PubMed

Affiliation: DSM/INAC/SPrAM (UMR 5819 CEA-CNRS-UJF)/LEMOH, CEA-Grenoble - 17 rue des Martyrs - 38054 Grenoble cedex 9, France. peter.reiss@cea.fr.

ABSTRACT
We address two aspects of general interest for the chemical synthesis of colloidal semiconductor nanocrystals: (1) the rational design of the synthesis protocol aiming at the optimization of the reaction parameters in a minimum number of experiments; (2) the transfer of the procedure to the gram scale, while maintaining a low size distribution and maximizing the reaction yield. Concerning the first point, the design-of-experiment (DOE) method has been applied to the synthesis of colloidal CdSe nanocrystals. We demonstrate that 16 experiments, analyzed by means of a Taguchi L16 table, are sufficient to optimize the reaction parameters for controlling the mean size of the nanocrystals in a large range while keeping the size distribution narrow (5-10%). The DOE method strongly reduces the number of experiments necessary for the optimization as compared to trial-and-error approaches. Furthermore, the Taguchi table analysis reveals the degree of influence of each reaction parameter investigated (e.g., the nature and concentration of reagents, the solvent, the reaction temperature) and indicates the interactions between them. On the basis of these results, the synthesis has been scaled up by a factor of 20. Using a 2-L batch reactor combined with a high-throughput peristaltic pump, different-sized samples of CdSe nanocrystals with yields of 2-3 g per synthesis have been produced without sacrificing the narrow size distribution. In a similar setup, the gram-scale synthesis of CdSe/CdS/ZnS core/shell/shell nanocrystals exhibiting a fluorescence quantum yield of 81% and excellent resistance of the photoluminescence in presence of a fluorescent quencher (aromatic thiol) has been achieved.PACS: 81.20.Ka, 81.07.Bc, 78.67.Bf.

No MeSH data available.