Fig. 1. (a) UV-visible absorption spectra (red), emission spectrum excited at 365 nm (blue) of a suspension of CDs. Insets: CD suspension under daylight (left) and 365 nm UV irradiation; (b) PL emission spectra of CDs at 10 ng ml⁻¹ recorded for excitation at progressively higher wavelengths from 270 to 620 nm.