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Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots.

Sai LM, Kong XY - Nanoscale Res Lett (2011)

Bottom Line: A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported.The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity.The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Material Science and Engineering, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai 200240, People's Republic of China. xykong@sjtu.edu.cn.

ABSTRACT
A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported. The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity. The core/shell quantum dots exhibit tunable fluorescence emissions by controlling the thickness of the CdSe shell. The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell.

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Wavelength shift and PL intensity of CdTe/CdSe core/shell QDs. The PL intensities of the as-prepared QDs solutions were estimated from the samples diluted to a certain concentration with the same absorbance values at the wavelength of their first excitation absorption peak. (a) Wavelength shift and corresponding PL intensity of CdTe/CdSe QDs versus different absorption values of the CdSe precursor solution. (b) PL spectra of CdTe/CdSe core/shell QDs synthesized with different [Se2-]/[Cd2+] molar ratio. (c) PL intensity of CdTe/CdSe QDs versus different [Cd2+]/[MPA] molar ratio. (d) PL intensity of CdTe and CdTe/CdSe QDs versus the UV-illuminated treatment time.
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Figure 3: Wavelength shift and PL intensity of CdTe/CdSe core/shell QDs. The PL intensities of the as-prepared QDs solutions were estimated from the samples diluted to a certain concentration with the same absorbance values at the wavelength of their first excitation absorption peak. (a) Wavelength shift and corresponding PL intensity of CdTe/CdSe QDs versus different absorption values of the CdSe precursor solution. (b) PL spectra of CdTe/CdSe core/shell QDs synthesized with different [Se2-]/[Cd2+] molar ratio. (c) PL intensity of CdTe/CdSe QDs versus different [Cd2+]/[MPA] molar ratio. (d) PL intensity of CdTe and CdTe/CdSe QDs versus the UV-illuminated treatment time.

Mentions: In order to obtain the appreciated properties of the as-received core/shell QDs, the synthesis conditions were optimized. Figure 3a shows that the wavelength shift and PL intensity of CdTe/CdSe QDs are strongly influenced by the CdTe concentration. All the CdTe/CdSe QD solutions were diluted to a certain concentration for the same absorbance values at the wavelength of their first excitation absorption peak, which was also used for the excitation of the QD samples in the PL measurement. The molar ratio of [Cd2+]/[MPA]/[HSe-] was set as 1:2.4:1, the concentration of Cd2+ was fixed at 1.25 mM, the reaction temperature was set at 100°C, and the reaction time was about 3 min. Here, we use the absorption values at the first excitation absorption peak of the CdTe QDs to represent the concentration of CdTe core QDs dispersed in the CdSe precursor solution. The wavelength shift refers to the emission wavelength difference of CdTe/CdSe core/shell QDs and CdTe core QDs. When this concentration was small, there would be much Se2- existing around each CdTe QD, therefore resulting in the fast coating of the CdSe shell. The wavelength shift increased with the thicker CdSe shell. When the concentration was too high (e.g., absorption value at 1.0), there would be too few Se2- for shell coating, and the emission wavelength almost did not shift. On the other hand, the PL intensity gradually decreased with the decreasing absorption value, which shows that fast coating will lead to a larger amount of surface defects and thus decrease of PL intensity. In our experiment, the proper range of CdTe absorption value was set about 0.5 to 0.7.


Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots.

Sai LM, Kong XY - Nanoscale Res Lett (2011)

Wavelength shift and PL intensity of CdTe/CdSe core/shell QDs. The PL intensities of the as-prepared QDs solutions were estimated from the samples diluted to a certain concentration with the same absorbance values at the wavelength of their first excitation absorption peak. (a) Wavelength shift and corresponding PL intensity of CdTe/CdSe QDs versus different absorption values of the CdSe precursor solution. (b) PL spectra of CdTe/CdSe core/shell QDs synthesized with different [Se2-]/[Cd2+] molar ratio. (c) PL intensity of CdTe/CdSe QDs versus different [Cd2+]/[MPA] molar ratio. (d) PL intensity of CdTe and CdTe/CdSe QDs versus the UV-illuminated treatment time.
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Figure 3: Wavelength shift and PL intensity of CdTe/CdSe core/shell QDs. The PL intensities of the as-prepared QDs solutions were estimated from the samples diluted to a certain concentration with the same absorbance values at the wavelength of their first excitation absorption peak. (a) Wavelength shift and corresponding PL intensity of CdTe/CdSe QDs versus different absorption values of the CdSe precursor solution. (b) PL spectra of CdTe/CdSe core/shell QDs synthesized with different [Se2-]/[Cd2+] molar ratio. (c) PL intensity of CdTe/CdSe QDs versus different [Cd2+]/[MPA] molar ratio. (d) PL intensity of CdTe and CdTe/CdSe QDs versus the UV-illuminated treatment time.
Mentions: In order to obtain the appreciated properties of the as-received core/shell QDs, the synthesis conditions were optimized. Figure 3a shows that the wavelength shift and PL intensity of CdTe/CdSe QDs are strongly influenced by the CdTe concentration. All the CdTe/CdSe QD solutions were diluted to a certain concentration for the same absorbance values at the wavelength of their first excitation absorption peak, which was also used for the excitation of the QD samples in the PL measurement. The molar ratio of [Cd2+]/[MPA]/[HSe-] was set as 1:2.4:1, the concentration of Cd2+ was fixed at 1.25 mM, the reaction temperature was set at 100°C, and the reaction time was about 3 min. Here, we use the absorption values at the first excitation absorption peak of the CdTe QDs to represent the concentration of CdTe core QDs dispersed in the CdSe precursor solution. The wavelength shift refers to the emission wavelength difference of CdTe/CdSe core/shell QDs and CdTe core QDs. When this concentration was small, there would be much Se2- existing around each CdTe QD, therefore resulting in the fast coating of the CdSe shell. The wavelength shift increased with the thicker CdSe shell. When the concentration was too high (e.g., absorption value at 1.0), there would be too few Se2- for shell coating, and the emission wavelength almost did not shift. On the other hand, the PL intensity gradually decreased with the decreasing absorption value, which shows that fast coating will lead to a larger amount of surface defects and thus decrease of PL intensity. In our experiment, the proper range of CdTe absorption value was set about 0.5 to 0.7.

Bottom Line: A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported.The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity.The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Material Science and Engineering, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai 200240, People's Republic of China. xykong@sjtu.edu.cn.

ABSTRACT
A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported. The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity. The core/shell quantum dots exhibit tunable fluorescence emissions by controlling the thickness of the CdSe shell. The photoluminescent properties were dramatically improved through UV-illuminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell.

No MeSH data available.


Related in: MedlinePlus