UV−vis absorption and fluorescence spectra of C-dots were investigated in aqueous solution (1 mg/mL) (Figure S2a). The absorption band was observed at 300 nm. The fluorescence spectra of the C-dots were highly dependent on the excitation wavelength (Figure S2b); therefore, any suitable excitation wavelength of C-dots could be employed to match a specific energy acceptor. The emission band position varied according to the different excitation wavelengths, primarily because of different emissive sites on the C-dots.59−61 Upon excitation at 340 nm, the C-dots solution showed blue emission with the most intensified intensity around 410 nm, and the emission band was gradually red-shifted with excitation wavelength variation.