Excitation wavelength-dependent quantum yield in water-soluble CdTe quantum dots

Area of Science:

• Materials Science
• Nanotechnology
• Photochemistry

Background:

• Semiconductor quantum dots (QDs) exhibit fluorescence intermittency, limiting their quantum yield (QY).
• Typically, QD QY increases with excitation wavelength, a phenomenon observed in many QD systems.

Purpose of the Study:

• To investigate the excitation wavelength-dependent quantum yield (QY) in water-soluble cadmium telluride quantum dots (CQDs).
• To elucidate the underlying mechanisms responsible for unusual QY behavior in CQDs.

Main Methods:

• Single-particle spectroscopy to analyze fluorescence intermittency and dark states.
• Fluorescence correlation spectroscopy (FCS) to quantify dark particle populations.
• Deuterium oxide/water exchange experiments to probe the role of protons (H+ ions).
• Cell internalization studies to assess imaging brightness at different wavelengths.

Main Results:

• Observed a decrease in CQD QY with increasing excitation wavelength, a deviation from typical QD behavior.
• Identified an increase in permanently dark single particles at longer excitation wavelengths.
• Confirmed the influence of H+ ions in water on the formation of these dark states.
• Demonstrated reduced imaging brightness for CQDs at longer wavelengths in cellular studies.

Conclusions:

• The excitation wavelength-dependent QY in CQDs is governed by an increase in dark states at longer wavelengths.
• Protons in aqueous solutions play a critical role in inducing these persistent dark states.
• Understanding this phenomenon is crucial for optimizing QD applications in various devices and imaging.