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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.

No MeSH data available.


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Optical performance of CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The optical performance of a series of original CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The QD samples are excited at their first excitation absorption peak, and The PL intensities of all the samples are normalized. (a) Fluorescence spectra of CdTe cores (black line) and CdTe/CdSe core/shell QDs with controlled reaction time under microwave irradiation, giving rise to the different CdSe shell thickness surrounding the CdTe core. The molar ratio of [Cd2+]/[MPA]/[Se2-] was set as 1:2.4:1, the concentration of Cd2+ was fixed at 1.25 mM, reaction temperature at about 100°C, and reaction time range from 2 min to approximately 20 min. (b) Fluorescence decay curves of a CdTe core (black line) and the CdTe/CdSe core/shell QDs (red line). The lifetimes were recorded at the maxima of the emission with the excitation wavelength of 371 nm. The inset picture indicates the fluorescence spectra of the corresponding QDs. The decay lifetime increases dramatically due to the coating of CdSe shell (reaction time of about 5 min under microwave irradiation).
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Figure 2: Optical performance of CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The optical performance of a series of original CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The QD samples are excited at their first excitation absorption peak, and The PL intensities of all the samples are normalized. (a) Fluorescence spectra of CdTe cores (black line) and CdTe/CdSe core/shell QDs with controlled reaction time under microwave irradiation, giving rise to the different CdSe shell thickness surrounding the CdTe core. The molar ratio of [Cd2+]/[MPA]/[Se2-] was set as 1:2.4:1, the concentration of Cd2+ was fixed at 1.25 mM, reaction temperature at about 100°C, and reaction time range from 2 min to approximately 20 min. (b) Fluorescence decay curves of a CdTe core (black line) and the CdTe/CdSe core/shell QDs (red line). The lifetimes were recorded at the maxima of the emission with the excitation wavelength of 371 nm. The inset picture indicates the fluorescence spectra of the corresponding QDs. The decay lifetime increases dramatically due to the coating of CdSe shell (reaction time of about 5 min under microwave irradiation).

Mentions: The optical performance of a series of original CdTe cores and corresponding CdTe/CdSe type II QDs synthesized at 100°C with different reaction times were examined, as shown in Figure 2a. It shows the continuous red shift in emission with the coating of CdSe shells onto CdTe core QDs. When the reaction or coating CdSe shell time is up to 20 min, the emission wavelength shifted to 665 nm, with an increase of 120 nm compared to the CdTe core QDs whose emission peak appeared at 545 nm. The thickness of the CdSe shell is observed as up to four or five atomic layers surrounding the CdTe cores with a 2-nm radius. As the reaction time increases, the CdSe shell coating proceeds and results in longer wavelengths of the emission shift. This clearly indicates the strong type II characteristics as the excitons become more spatially separated by thicker shells. Therefore, the PL peak can be assigned to an indirect excitation, originating from the radiative recombination of electron hole pairs across the core/shell interface [14,15].


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

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

Optical performance of CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The optical performance of a series of original CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The QD samples are excited at their first excitation absorption peak, and The PL intensities of all the samples are normalized. (a) Fluorescence spectra of CdTe cores (black line) and CdTe/CdSe core/shell QDs with controlled reaction time under microwave irradiation, giving rise to the different CdSe shell thickness surrounding the CdTe core. The molar ratio of [Cd2+]/[MPA]/[Se2-] was set as 1:2.4:1, the concentration of Cd2+ was fixed at 1.25 mM, reaction temperature at about 100°C, and reaction time range from 2 min to approximately 20 min. (b) Fluorescence decay curves of a CdTe core (black line) and the CdTe/CdSe core/shell QDs (red line). The lifetimes were recorded at the maxima of the emission with the excitation wavelength of 371 nm. The inset picture indicates the fluorescence spectra of the corresponding QDs. The decay lifetime increases dramatically due to the coating of CdSe shell (reaction time of about 5 min under microwave irradiation).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211493&req=5

Figure 2: Optical performance of CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The optical performance of a series of original CdTe cores and corresponding CdTe/CdSe type II QDs by means of microwave-assisted synthesis. The QD samples are excited at their first excitation absorption peak, and The PL intensities of all the samples are normalized. (a) Fluorescence spectra of CdTe cores (black line) and CdTe/CdSe core/shell QDs with controlled reaction time under microwave irradiation, giving rise to the different CdSe shell thickness surrounding the CdTe core. The molar ratio of [Cd2+]/[MPA]/[Se2-] was set as 1:2.4:1, the concentration of Cd2+ was fixed at 1.25 mM, reaction temperature at about 100°C, and reaction time range from 2 min to approximately 20 min. (b) Fluorescence decay curves of a CdTe core (black line) and the CdTe/CdSe core/shell QDs (red line). The lifetimes were recorded at the maxima of the emission with the excitation wavelength of 371 nm. The inset picture indicates the fluorescence spectra of the corresponding QDs. The decay lifetime increases dramatically due to the coating of CdSe shell (reaction time of about 5 min under microwave irradiation).
Mentions: The optical performance of a series of original CdTe cores and corresponding CdTe/CdSe type II QDs synthesized at 100°C with different reaction times were examined, as shown in Figure 2a. It shows the continuous red shift in emission with the coating of CdSe shells onto CdTe core QDs. When the reaction or coating CdSe shell time is up to 20 min, the emission wavelength shifted to 665 nm, with an increase of 120 nm compared to the CdTe core QDs whose emission peak appeared at 545 nm. The thickness of the CdSe shell is observed as up to four or five atomic layers surrounding the CdTe cores with a 2-nm radius. As the reaction time increases, the CdSe shell coating proceeds and results in longer wavelengths of the emission shift. This clearly indicates the strong type II characteristics as the excitons become more spatially separated by thicker shells. Therefore, the PL peak can be assigned to an indirect excitation, originating from the radiative recombination of electron hole pairs across the core/shell interface [14,15].

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