Long-term effects of impurities on the particle size and optical emission of carbon dots

Carbon dots (CDs) are fluorescent nanoparticles that exhibit strong photoluminescence (PL) emission throughout the visible range of the electromagnetic spectrum. Recent studies highlight the presence of fluorescent impurities in CD dispersions. Here, the long-term impact of these impurities on the stability of the physical and optical properties of CDs synthesized by the solvothermal method is studied. A significant increase in particle size is observed as a function of time after synthesis from transmission electron microscopy analysis of CDs. Furthermore, the quantum yield of blue PL emission, which is mostly caused by impurities that contain carboxyl groups, gradually decays from 30% to similar to 3% over 13 weeks. The reduction in quantum yield is attributed to decomposition of impurities that, consequently, deposit on the particles and increase particle size. Finally, it is observed that the blue emission decreases considerably when CDs are properly purified and a solvent-dependent yellow emission arises. The yellow emission is almost negligible when CDs are dispersed in water; however, the intensity of yellow emission increases significantly when the concentration of ethanol is increased.

Automated summary

This study explores the long-term impact of fluorescent impurities in CDs on their stability, leading to a significant increase in particle size over time and a gradual decay in the quantum yield of blue PL emission. It is found that the reduction in quantum yield is due to the decomposition of impurities, which deposit on the particles and increase their size. Additionally, purification of CDs results in a decrease in blue emission and the emergence of a solvent-dependent yellow emission, with ethanol concentration affecting the intensity of the yellow emission.