Deposition of CdSe quantum dots on graphene sheets

High-quality TOP/TOPO capped CdSe quantum dots (QDs) displaying a narrow emission band have been grafted on to graphene nanosheets through a simple wet chemical procedure. A significant red-shift of both the broad absorption and narrow emission spectra of the QDs is induced in the resultant hybrid material, presumably by a strong graphene-QD interaction consistent with a quantum tunnelling phenomenon. The optical properties of monodisperse CdSe QDs of 3-4 nm in diameter have been determined in UV-vis and photoluminescence spectra and HRTEM and XPS data, demonstrating the successful decoration of graphene sheets with CdSe QDs. The CdSe QD absorption was observed to shift to longer wavelengths by up to 30 nm, with a corresponding shift of up to 18 nm observed in the emission band. This effect is equivalent to a narrowing of the band gap by 0.094±0.015 eV in absorption and 0.033±0.013 eV in emission, or an interaction potential of 9.1±1.5 kJ mol−1. Another is to consider the effective particle growth based upon the narrowed band gap, consistently found to be 28±1%, despite the physical size remaining unchanged. By effectively shifting the absorption and emission of CdSe QDs to longer wavelengths, this type of nanocomposite may have potential applications in the fields of optics, biological imaging and sensing.