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Zero-Threshold Optical Gain in Electrochemically Doped Nanoplatelets and the Physics Behind It
Jaco J Geuchies1, Robbert Dijkhuizen1, Marijn Koel1
1Optoelectronic Materials Section, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2926 HZDelft, The Netherlands.
ACS Nano
|October 18, 2022
Summary
Electrochemical n-doping significantly enhances colloidal nanoplatelets (NPLs) for lasing. These doped NPLs exhibit superior optical gain performance compared to quantum dots, with a minimal gain threshold and broad spectral range.
Area of Science:
- Materials Science
- Nanotechnology
- Optoelectronics
Background:
- Colloidal nanoplatelets (NPLs) are explored for lasing due to 2D material-like properties and strong excitonic effects.
- NPLs possess finite lateral dimensions, deviating from true 2D structures, influencing their optical characteristics.
- Excitonic effects and exciton binding energy are key factors in NPL optical properties and gain performance.
Purpose of the Study:
- To investigate the photophysics and optical gain properties of CdSe/CdS/ZnS core-shell-shell NPLs.
- To explore the impact of electrochemical n-doping on NPL gain performance and optical transitions.
- To determine if NPLs can achieve superior gain medium performance compared to existing colloidal nanomaterials.
Main Methods:
- Fabrication of CdSe/CdS/ZnS core-shell-shell nanoplatelets.
- Electrochemical n-doping of the NPLs.
- Photoluminescence (PL) and absorption spectroscopy to study optical properties.
- Transient absorption spectroscopy to measure gain thresholds and coefficients.
- Comparison of NPLs with colloidal quantum dots (CQDs).
Main Results:
- Reduced excitonic effects observed in core-shell-shell NPLs due to decreased exciton binding energy.
- A low gain threshold of one excitation per nanoplatelet was measured.
- Electrochemical n-doping led to complete bleaching of band edge exciton transitions.
- Doped NPLs showed a complete removal of the gain threshold over a broad spectral range.
- Achieved gain coefficients of several thousand cm-1, significantly outperforming n-doped CQDs.
- Optimal lateral size for minimal gain threshold per nm2 was identified.
Conclusions:
- CdSe/CdS/ZnS core-shell-shell NPLs, when electrochemically n-doped, represent the best colloidal nanomaterial gain medium reported to date.
- The unique properties of NPLs, balancing quantum confinement and 2D material characteristics, are ideal for optical gain.
- Electrochemical doping effectively suppresses excitonic effects and unlocks broad, high-gain optical properties in NPLs.
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