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Dynamic Evolution from Negative to Positive Photocharging in Colloidal CdS Quantum Dots.
Donghai Feng1,2, Dmitri R Yakovlev1,3, Victor V Pavlov3
1Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany.
Nano Letters
|April 4, 2017
Summary
Photocharging in cadmium sulfide (CdS) quantum dots (QDs) shifts from negative to positive due to carrier trapping dynamics. This study reveals insights into emission blinking in colloidal nanostructures.
Area of Science:
- Materials Science
- Nanotechnology
- Physical Chemistry
Background:
- Optical properties of colloidal semiconductor nanocrystals are significantly affected by charge carrier trapping on their surfaces.
- Surface traps and varying capture rates lead to dynamic charging of neutral nanocrystals.
Purpose of the Study:
- To investigate the formation and evolution dynamics of photocharging in CdS colloidal quantum dots (QDs).
- To understand the underlying mechanisms of carrier trapping and detrapping influencing QD charging states.
Main Methods:
- Development of a time-resolved technique using three laser pulses (pump, orientation, probe) for picosecond resolution.
- Monitoring photocharging dynamics across a wide timescale (picoseconds to milliseconds).
- Detection based on coherent electron spin dynamics to differentiate between electron and hole carriers within the QD core.
Main Results:
- Initially, fast hole trapping causes negative photocharging in CdS QDs.
- The system evolves to positive photocharging due to subsequent electron trapping and hole detrapping.
- Positive photocharging persists for hundreds of microseconds at room temperature.
Conclusions:
- The study elucidates the complex dynamics of photocharging in colloidal QDs.
- Findings offer crucial insights into the mechanisms behind emission blinking in nanostructures.
- Understanding photocharging is vital for controlling optical properties and applications of QDs.