Photocycle of Excitons in Nitrogen-Rich Carbon Nanodots: Implications for Photocatalysis and Photovoltaics

Nitrogen-rich carbon nanodots have emerged as promising nanomaterials for a wide range of applications where a highly emissive and photoactive material with low toxicity and cost-effectiveness is required. One of their hallmarks is indeed a bright, tunable fluorescence of excitonic nature. Disentangling the origin of their optical absorption and fluorescence properties and uncovering relaxation channels and interactions with solvents are some of the most debated issues in the field. Uncovering these aspects is essential for targeted applications, especially in the fields of photocatalysis but also photovoltaics and optoelectronics. Here, we present dedicated transient absorption measurements of purified monodispersed nanodots covering all relevant electronic transitions. Monodispersed nanodots of about 6 nm size exhibit well-separated absorption and emission features and allow us to unambiguously establish the complete and size-independent femtosecond-to-nanosecond photocycle of nitrogen-rich carbon nanodots. Further rigorous analysis shows that the often complex absorption and emission spectra of an ensemble of nanodots with a broad size distribution result from the superposition of individual size-selective contributions.