On the upconversion fluorescence in carbon nanodots and graphene quantum dots

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Carbon nanodots (CNDs) and graphene quantum dots (GQDs) are widely believed to possess upconversion fluorescence properties.
• These properties have led to proposed mechanisms and potential applications in various fields.

Purpose of the Study:

• To investigate the presence and origin of upconversion fluorescence in synthesized CNDs and GQD samples.
• To critically re-evaluate the commonly accepted understanding of upconversion fluorescence in these nanomaterials.

Main Methods:

• Synthesis of five distinct batches of CNDs and GQDs.
• Characterization using fluorescence spectrophotometry.
• Analysis of excitation intensity dependence of fluorescence emission.

Main Results:

• No evidence of intrinsic upconversion fluorescence was observed in any of the synthesized CNDs and GQD samples.
• The apparent upconversion fluorescence was identified as normal fluorescence.
• This artifact arises from excitation by light leaking from the second diffraction order of the monochromator in the fluorescence spectrophotometer.

Conclusions:

• The phenomenon attributed to upconversion fluorescence in CNDs and GQD research is likely an artifact.
• Proper experimental controls, such as measuring excitation intensity dependence, are crucial for accurate interpretation of fluorescence data.
• This finding necessitates a re-examination of previous studies and proposed applications based on purported CND and GQD upconversion fluorescence.