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(a) UV-vis absorbance (Abs), FL excitation (Ex) (355 nm), and emission (Em) (439 nm) spectra of N-CDs (inset: pictures of CD solution irradiated with daylight and UV light). (b) Excitation-dependent emission with the excitation wavelength of 315–455 nm. The figure is reprinted with permission from Ref. [65]. Copyright belongs to Elsevier. Abbreviations: FL: fluorescence.
