Switching between Plasmonic and Fluorescent Copper Sulfide Nanocrystals.

Area of Science:

• Materials Science
• Nanotechnology
• Electrochemistry

Background:

• Doping density in copper sulfide nanocrystals is crucial for optoelectronic applications.
• Existing methods lack precise, reversible control over carrier density.

Purpose of the Study:

• To demonstrate reversible control of hole carrier density in copper sulfide nanocrystals.
• To explore electrochemical methods for tuning doping and phase transitions.
• To enable switching between plasmonic and fluorescent properties.

Main Methods:

• Electrochemical methods utilizing different charge compensating cations (e.g., Li+, Cu+).
• Investigating capacitive charging versus ion intercalation.
• Characterizing phase transitions and optical properties (band gap, plasmon resonance, fluorescence).

Main Results:

• Reversible control of hole carrier density from >10^22 cm^-3 to intrinsic achieved.
• Lithium intercalation enables reversible switching between covellite CuS (plasmonic) and low-chalcocite CuLiS (semiconducting) phases.
• Copper ion intercalation induces a permanent phase transition to intrinsic low-chalcocite Cu2S, exhibiting stable near-infrared fluorescence (~1050 nm).

Conclusions:

• Electrochemical control offers dynamic tuning of copper sulfide nanocrystal properties.
• The ability to switch between plasmonic and fluorescent states is demonstrated.
• These findings pave the way for applications in photovoltaic devices, NIR optical switches, and smart windows.