Shell and ligand-dependent blinking of CdSe-based core/shell nanocrystals.
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.
Chon
Bonghwan
B
Bio-Nanotechnology Center, Department of Chemistry, Pohang University of Science and Technology, San31 Hyoja-dong Nam-gu, Pohang, Kyungbuk 790-784, Korea.
Lim
Sung Jun
SJ
Kim
Wonjung
W
Seo
Jongcheol
J
Kang
Hyeonggon
H
Joo
Taiha
T
Hwang
Jeeseong
J
Shin
Seung Koo
SK
D019187:Cadmium Compounds / Q000737:chemistry*; D008024:Ligands; D053758:Nanoparticles / Q000737:chemistry*; D018036:Selenium Compounds / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry; D013816:Thermodynamics; D017967:Zinc Compounds / Q000737:chemistry
D019187:Cadmium Compounds; D008024:Ligands; D018036:Selenium Compounds; D013440:Sulfides; D017967:Zinc Compounds; C034939:cadmium sulfide; C058667:cadmium selenide; C031238:zinc sulfide; C044696:zinc selenide