Fig. 3. (A) Absorbance (black), excitation for 450 nm emission (red) emission for 350 nm excitation (dark blue), emission for 250 nm excitation (light blue), excitation reconstructed from wavelength dependent emission (green), spectra of an aqueous suspension of carbon nanofibers. Blue star represents deleted data corresponding to the second harmonic of the light blue emission spectrum. (B) Emission spectra taken at 20 nm incremental excitations from 290 nm (blue line) to 450 nm (purple line) showing little excitation dependent shift. Inset shows photographs of a sample in the cuvette the measurements were recorded in natural light and under 365 nm UV lamp. (C) Lifetime of carbon nanofiber suspension, in aqueous solution at pH 6.8. (D) Graph showing the effect of pH on emission at 350 nm excitation and (inset) its reversibility.