Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots
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NANO EXPRESS
Open Access
Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots Li-Man Sai and Xiang Yang Kong*
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 UVilluminated treatment, and the time-resolved fluorescence spectra showed that there is a gradual increase of decay lifetime with the thickness of CdSe shell. Introduction 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. [1,2]. The unique optical properties are featured as narrow emission spectra, continuous absorption band, high chemical and photobleaching stability, and surface functionality. To date, QDs have various nanostructured configurations, typically as core/shell heterostructure QDs, where two different semiconductors are incorporated into a single colloidal QD [3]. 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 [4]. 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 [5]. 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 [6]. Recently, the high-quality CdTe/CdSe heterostructure QDs have been successfully synthesized via colloidal chemical routes [7-9]. However, these synthetic methods * Correspondence: [email protected] School of Material Science and Engineering, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai 200240, People’s Republic of China
cost several hours in an organic solvent at high temperature, and the product easily performed the agglomeration with broad size distribution. It is desirable to develop a facile method for fast synthesis of highly fluorescent type II core/shell QDs in aqueous ion solution. 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 [10-12]. In this paper, we employed the microwave-assisted synthesis in aqueous solution for the water-dispersed CdTe/CdSe core/shell type II nanocryst
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