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Shell and ligand-dependent blinking of CdSe-based core/shell nanocrystals
Bonghwan Chon1, Sung Jun Lim, Wonjung Kim
1Bio-Nanotechnology Center, Department of Chemistry, Pohang University of Science and Technology, San31 Hyoja-dong Nam-gu, Pohang, Kyungbuk 790-784, Korea.
Physical Chemistry Chemical Physics : PCCP
|July 8, 2010
Summary
Blinking in cadmium selenide (CdSe) core/shell nanocrystals depends on shell materials and ligands. Thiolate passivation and specific shell structures like CdSe/CdS/ZnS enhance light emission stability.
Area of Science:
- Materials Science
- Nanotechnology
- Physical Chemistry
Background:
- Semiconductor nanocrystals, particularly cadmium selenide (CdSe)-based core/shell structures, are crucial for optoelectronic applications.
- The phenomenon of photoluminescence blinking, characterized by intermittent light emission, limits their performance.
- Understanding blinking dynamics is essential for designing stable and efficient nanocrystal-based devices.
Purpose of the Study:
- To investigate the influence of different shell materials and surface ligands on the blinking behavior of CdSe core/shell nanocrystals.
- To correlate blinking dynamics with core/shell structure and surface chemistry.
- To present a model explaining the observed blinking variations.
Main Methods:
- Colloidal synthesis of CdSe/ZnS, CdSe/ZnSe/ZnS, and CdSe/CdS/ZnS core/shell nanocrystals.
- Ligand exchange to convert organic-soluble nanocrystals to water-soluble ones using 3-mercaptopropionic acid.
- Characterization using absorption, emission spectroscopy, photoluminescence lifetime measurements, and single-nanocrystal blinking time trace analysis.
- Fitting of on- and off-time distributions to power-law models.
Main Results:
- Blinking behavior (on- and off-time distributions) is significantly influenced by shell materials and surface ligands.
- Water-soluble surface passivation with thiolate ligands consistently prolongs the non-emissive (off) state.
- The CdSe/CdS/ZnS core/shell structure demonstrated the longest emissive (on) state duration.
- Power-law exponents for on- and off-times were found to be inversely correlated.
Conclusions:
- Surface passivation and core/shell architecture are critical factors in controlling nanocrystal blinking.
- Thiolate ligands enhance the stability of the non-emissive state, while specific shell compositions (e.g., CdSe/CdS/ZnS) optimize the emissive state.
- A two competing charge-tunneling model effectively explains the observed variations in blinking exponents.
