Fig. 1. (A) UV-vis absorption and fluorescence spectra of S, N, O-CDs under different excitation wavelengths. (B) High resolution XPS spectra of the S 2p region of S, N, O-CDs. (C) TEM image of S, N, O-CDs. The insets show a high resolution TEM image and the particle distribution of the S, N, O-CDs. (D) AFM image of S, N, O-CDs. Inset shows the corresponding height distribution of S, N, O-CDs along the axis.
