Size and Dopant Dependent Single Particle Fluorescence Properties of Graphene Quantum Dots

The emissive properties of both doped and nondoped graphene quantum dots (GQDs) with sizes ranging from 3 to 11 nm were analyzed at the single particle level. Both doped and nondoped GQDs are a composite of particles exhibiting green, red, or NIR fluorescence on excitation at 488, 561, and 640 nm, respectively. Nitrogen-doped GQDs (N-GQDs) with diameters ranging from 3.4 to 5.2 nm show a larger proportion of particles with NIR emission as compared to nondoped particles. Doping of GQDs also resulted in changes in the photostability and the fluorescence intermittency seen in single GQD particles. While milliseconds to seconds time scale blinking was regularly observed for red-emitting nondoped GQDs, nitrogen doping significantly reduced blinking. Both doped and nondoped particles also exhibit moderate size dependent photophysical properties.