Ultrafast insights into full-colour light-emitting C-Dots

Designing carbon dots (C-Dots) in a controlled way requires a profound understanding of their photophysical properties, such as the origin of their fluorescence and excitation wavelength-dependent emission properties, which has been a perennial problem in the last few decades. Herein, we synthesized three different C-Dots (blue, green, and red-emitting C-Dots) from the same starting materials via a hydrothermal method and separated them by silica column chromatography. All the purified C-Dots exhibited three different emission maxima after a certain range of different excitations, showing a high optical uniformity in their emission properties. It was also observed that the average distributions of the particle size in all the C-Dots were the same with a typical size of 4 nm and the same interplanar d spacing of similar to 0.21 nm. Here, we tried to establish a well-defined conclusive answer to the puzzling optical properties of C-Dots via successfully investigating the carrier dynamics of their core and surface state with a myriad use of steady-state, time-resolved photoluminescence, and ultrafast transient absorbance spectroscopy techniques. The ultrafast charge-carrier dynamics of the core and surface state clearly indicated that the graphitic nitrogen in the core state and the oxygen-containing functional group in the surface state predominately contribute to controlling their wide range of emission properties. We believe that these findings will give the C-Dots their own designation in the fluorophore world and create a new avenue for designing and developing C-Dot-based new architectures.

Automated summary

This study synthesized and separated C-Dots with different emission peaks and investigated their carrier dynamics to reveal the origin and control mechanism of their fluorescence properties. These findings are of great significance for the design and development of new architectures based on C-Dots.