Ligand-Controlled Microwave Synthesis of Cubic and Hexagonal CdSe Nanocrystals Supported on Graphene. Photoluminescence Quenching by Graphene

We have developed a facile, fast, and scalable microwave irradiation method for the synthesis of graphene and CdSe nanocrystals of controlled size, shape, and crystalline structure dispersed on graphene sheets. The reduction of graphite oxide into graphene takes place in DMSO within 2 min of microwave irradiation as opposed to 12 h of conventional thermal heating at 180 degrees C. The method allows the simultaneous reduction of graphite oxide and the nucleation and growth of CdSe nanocrystals using a variety of capping agents. Cubic and hexagonal CdSe nanocrystals with average sizes of 2-4 and 5-7 nm, respectively, have been prepared by the proper choice of the capping agent within a few minutes of microwave irradiation. High-quality nearly monodisperse CdSe nanocrystals have been supported on graphene with no evidence of aggregation. Direct evidence is presented for the efficient quenching of photoluminescence from the CdSe nanocrystals by graphene. The results provide a new approach for exploring the size-tunable optical properties of CdSe nanocrystals supported on graphene which could have important implications for energy conversion applications such as photovoltaic cells where CdSe quantum dots, the light-harvesting material, are supported on the highly conducting flexible graphene electrodes.