Fig. 2

a UV–vis absorption spectrum of the NIR-CDs dissolved in water (100 µg/mL), inset: digital photograph of the NIR-CDs solution under daylight. b Fluorescence excitation spectrum (black line) and emission spectra under varying excitation wavelengths of the NIR-CDs solution (10 µg/mL), inset: digital photograph of the NIR-CDs under the excitation of laser pointer (405 nm)