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Publication Citation: Shell and ligand-dependent blinking of CdSe-based core/shell nanocrystals

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Author(s): Bonghwan Chon; Sung Jun Lim; Wonjung Kim; Hyeong G. Kang; Taiha Joo; Jeeseong Hwang; Seung Koo Shin;
Title: Shell and ligand-dependent blinking of CdSe-based core/shell nanocrystals
Published: July 07, 2010
Abstract: Blinking of zinc blende CdSe-based core/shell nanocrystals is studied as a function of shell materials and surface ligands. CdSe/ZnS, CdSe/ZnSe/ZnS and CdSe/CdS/ZnS core/shell nanocrystals are prepared by colloidal synthesis and six monolayers of larger bandgap shell materials are grown over the CdSe core. Organic-soluble nanocrystals covered with stearate are made water-soluble by ligand exchange with 3-mercaptopropionic acid. The light-emitting states of nanocrystals are characterized by absorption and emission spectroscopy as well as photoluminescence lifetime measurements in solution. The blinking time trace is recorded for single nanocrystals on a glass coverslip. Both on- and off-time distributions are fitted to the power law. The power-law exponents vary, depending on shell materials and surface ligands. The off-time exponents for organic and water-soluble nanocrystals are measured in the range of 1.36 1.55 and 1.25 1.37, respectively, while their on-time exponents are spread in the range of 1.53 1.86 and 1.85 2.17, respectively. Water-soluble surface passivation with thiolate prolongs the dark period regardless of shell materials and core/shell structures. Of the core/shell structures, CdSe/CdS/ZnS exhibits the longest bright state. The on/off-time exponents are inversely correlated, although the successive on/off events are not individually correlated. A two competing charge-tunneling model is presented to describe the variation of on- and off-time exponents with shell materials and surface ligands.
Citation: Physical Chemistry and Chemical Physics
Volume: 12
Pages: pp. 9312 - 9319
Keywords: blinking; fluorescence; nanocrystal; quantum dot; single crystal
Research Areas: Characterization, Nanometrology, and Nanoscale Measurements, Quantitative Molecular Imaging