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Spectroscopy of Surface-State p-Doped CdSe/CdS Quantum Dots
David Morgan1, David F Kelley1
1Chemistry and Chemical Biology , University of California Merced , 5200 North Lake Road , Merced , California 95343 , United States.
The Journal of Physical Chemistry Letters
|July 12, 2018
Summary
Thermal surface charging in cadmium selenide/cadmium sulfide (CdSe/CdS) quantum dots (QDs) creates a p-type state. This leads to a 70 ps Auger recombination decay, confirmed by transient absorption and photoluminescence spectroscopy.
Area of Science:
- Materials Science
- Quantum Dot Spectroscopy
- Semiconductor Nanostructures
Background:
- II-VI quantum dots (QDs) exhibit complex surface phenomena.
- Thermal population of surface states influences QD electronic properties.
- Understanding surface charging is crucial for QD applications.
Purpose of the Study:
- To provide direct spectroscopic evidence for thermal surface charging in CdSe/CdS QDs.
- To investigate the role of surface states in photophysical processes.
- To elucidate the mechanism of Auger recombination in surface-charged QDs.
Main Methods:
- Transient Absorption (TA) spectroscopy.
- Time-Resolved Photoluminescence (PL) spectroscopy.
- Synthesis of CdSe/CdS core/shell quantum dots with chalcogenide-rich surfaces.
Main Results:
- Observed a 70 ps decay component in both TA and PL kinetics, attributed to Auger recombination of a surface-charged state (positive trion).
- Demonstrated that passivation of surface states with trialkylphosphine eliminates this fast decay component.
- Found a difference in the relative amplitude and spectral shift between TA and PL kinetics, supporting the trion assignment.
Conclusions:
- Direct spectroscopic evidence confirms thermal surface charging in CdSe/CdS QDs.
- Surface charging leads to the formation of a p-type state and subsequent Auger recombination.
- Ligand passivation effectively suppresses surface-induced recombination pathways.
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