![]() The optical density at the excitation wavelength of the Rhodamine 6G (R6G) and the QD samples in the solution were set to a similar value. The PLQY of QDs at room temperature was estimated using standard method. ![]() The UV-Vis absorption spectra were recorded with a Shimadzu UV-3150 UV-Vis-near-infrared spectrophotometer (Shimadzu Corporation, Columbia, MD, USA)The photoluminescence (PL) measurements were performed using a Shimadzu RF-6301PC spectrofluorimeter (Shimadzu Corporation, Columbia, MD, USA). The TEM images were recorded from a JEOL JEM 2100 electron microscope (JEOL, Tokyo, Japan) operated at 200 kV. The samples for transmission electron microscopy (TEM) were prepared by dropping the aqueous CdTe/CdSe solution onto carbon-coated copper grids with the excess solvent evaporated. The XRD patterns were recorded from a Rigaku D/max-γB diffractometer. The as-prepared QD samples were precipitated by 2-propanol and dried in a vacuum oven for X-ray diffraction (XRD) characterization. Structural characterizations and spectroscopic measurements The samples were taken when the temperature decreased naturally to lower than 50☌ and centrifuged for high concentration. The high-quality CdTe/CdSe QDs were prepared in a very short time, and the sizes of the QDs were controlled on the basis of regulating the reaction time of microwave irradiation. The concentration of Cd 2+ was fixed at 1.25 mM. The CdTe/CdSe precursor solution was prepared by adding a certain amount of postprepared CdTe core QDs to a N 2-saturated solution mixed with CdCl 2, NaHSe, and MPA in pH 11.2. Microwave-assisted synthesis of CdTe/CdSe core/shell QDs The CdTe core QDs stabilized with MPA were concentrated from the solution and were precipitated with 2-propanol by centrifugation, and then re-dissolved in ultrapure water. The as-prepared CdTe precursor solution is subjected to microwave irradiation for about 2 min at 100☌, and is naturally cooled down lower than 50☌. The molar ratio of Cd 2+/MPA/HTe - was set as 1:2.5:0.2. Microwave-assisted synthesis of CdTe core QDsįor monodispersed CdTe core QD synthesis, the CdTe precursor solution was prepared by adding a freshly prepared NaHTe solution to a N 2-saturated CdCl 2 solution in the presence of the stabilizer of 3-mercaptopropionic acid (MPA). These aqueous-dispersed CdTe/CdSe core/shell type II QDs may have potential applications in solar cells. The photoluminescence quantum yield (PLQY) of the as-prepared QDs was enhanced from 12% to as high as 45%. The optical properties of as-prepared CdTe/CdSe nanocrystals can be optimized in the presence of Cd 2+ and mercaptopropionic acid by UV-illuminated treatment. In this paper, we employed the microwave-assisted synthesis in aqueous solution for the water-dispersed CdTe/CdSe core/shell type II nanocrystals. A microwave-assisted synthesis is an attractive method employed routinely for the synthesis of nanocrystals due to the advantages of the reaction selectivity and high efficiency for obtaining the controllable products. It is desirable to develop a facile method for fast synthesis of highly fluorescent type II core/shell QDs in aqueous ion solution. However, these synthetic methods cost several hours in an organic solvent at high temperature, and the product easily performed the agglomeration with broad size distribution. Recently, the high-quality CdTe/CdSe heterostructure QDs have been successfully synthesized via colloidal chemical routes. Specifically, it has been reported that the CdTe/CdSe core/shell QDs exhibit type II band alignment facilitating charge separations upon absorption of visible light for solar cells. Type I is where both the electrons and holes are confined in the core, in contrast, type II is where the electrons and holes are separated between the core and the shell, giving rise to a significant increase in the exciton lifetime with possible applications in photovoltaics. There are type I and type II core/shell QDs with different carrier localizations, depending on the band structure offsets between the semiconducting core and the shell. To date, QDs have various nanostructured configurations, typically as core/shell heterostructure QDs, where two different semiconductors are incorporated into a single colloidal QD. The unique optical properties are featured as narrow emission spectra, continuous absorption band, high chemical and photobleaching stability, and surface functionality. Semiconducting nanocrystals such as quantum dots (QDs) have attracted more attention due to their unique optical properties and many potential applications including nanolasers, biolabelings, and photovoltaics, etc.
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