Probing photoluminescence dynamics of colloidal CdSe/ZnS core/shell nanoparticles

The paper presents the synthesis of thiol capped CdSe/ZnS core/shell nanoparticles with CdSe core and ZnS shell. The thickness of the ZnS shell has been controlled by the regulating the amount of Zn/S precursors for reaction. The steady and transient photoluminescence properties substantiate the growth of ZnS shell over the CdSe cores. High resolution transmission electron microscope and the X-ray diffraction patterns reveal nanocrystalline particles of an average size 3.4 nm packed in wurtzite lattice. Photoluminescence excitation spectra as well as the excitation-emission matrix of CdSe and CdSe/ZnS evidence the growth of ZnS for Type I hetero-junction without interfering the energy states of core. By this method, ZnS layer of 8.84 Å is optimum for fluorescence enhancement of the core/shell quantum dots. The multiexponential fluorescence decay of the quantum dots represents independent radiative recombinations with overlapped energies. It is revealed that the average fluorescence lifetimes of quantum dots decreased with increase in ZnS shell, which is due to the enhanced contribution from initially populated excitonic recombination and the reduction in the surface trap states with shell growth.