Fingerprinting photoluminescence of functional groups in graphene oxide

Chemically modified graphene oxide (GO) sheets exhibit three fingerprinting photoluminescent (PL) peaks, which originate from the sigma* -> n, pi* -> pi and pi* -> n electronic transitions between the antibonding and the bonding molecular orbitals. The three PL peaks are associated with the C-OH, the aromatic C=C and the C=O functional groups in the GO sheets, respectively. The relative intensities of the three PL peaks are modulated by varying the oxygen-containing functional groups. The three PL emission peaks exhibit a red-shift with an increase in the excitation wavelength. The difference between the emission peak and the excitation wavelength shows a constant Stokes shift of 53.3 nm, 112.1 nm and 217.9 nm for the sigma* -> n, pi* -> pi and pi* -> n transitions, respectively.