  Fluorescent organic compounds are of significant importance to the
development of low-cost opto-electronic devices. Blue fluorescence from
aromatic or olefinic molecules and their derivatives is particularly important
for display and lighting applications. Thin film deposition of
low-molecular-weight fluorescent organic compounds typically requires costly
vacuum evaporation systems. On the other hand, solution-processable polymeric
counterparts generally luminesce at longer wavelengths due to larger
delocalization in the chain. Blue light emission from solution-processed
materials is therefore of unique technological significance. Here we report
near-UV to blue photoluminescence (PL) from solution-processed graphene oxide
(GO). The characteristics of the PL and its dependence on the reduction of GO
indicates that it originates from the recombination of electron-hole (e-h)
pairs localized within small sp2 carbon clusters embedded within an sp3 matrix.
These results suggest that a sheet of graphene provides a parent structure on
which fluorescent components can be chemically engineered without losing the
macroscopic structural integrity. Our findings offer a unique route towards
solution-processable opto-electronics devices with graphene.
