Carbon dots (CDs) are new carbon-based photoluminescence (PL) nanomaterials with a core-shell motif. Due to their fascinating advantages, such as chemical inertness, high quantum yields (QYs), high water solubility, thermal stability, and excellent biocompatibility, CDs have attracted extensive attention in various research applications, such as cancer diagnosis, phototherapy, and optoelectronic devices. However, the underlying PL phenomena of CDs remain a mystery due to the polydispersity of the products and the difficulty in ascertaining their atomic structures.