  Photoluminescence of graphene quantum dots (GQDs) of shungite, attributed to
individual fragments of reduced graphene oxide (rGO), has been studied for the
frozen rGO colloidal dispersions in water, carbon tetrachloride, and toluene.
Morphological study shows a steady trend of GQDs to form fractals and a drastic
change in the colloids fractal structure caused by solvent was reliably
established. Spectral study reveals a dual character of emitting centers:
individual GQDs are responsible for the spectra position while fractal
structure of GQD colloids provides high broadening of the spectra due to
structural inhomogeneity of the colloidal dispersions and a peculiar dependence
on excitation wavelength. For the first time, photoluminescence spectra of
individual GQDs were observed in frozen toluene dispersions which pave the way
for a theoretical treatment of GQD photonics.
