Fingerprinting photoluminescence of functional groups in graphene oxide

Chemically modified graphene oxide (GO) sheets exhibit three "fingerprinting" photoluminescent (PL) peaks, which originate from the σ* → n, π* → π and π* → n electronic transitions between the antibonding and the bonding molecular orbitals. The three PL peaks are associated with the C–OH, the aromatic CC and the CO 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 σ* → n, π* → π and π* → n transitions, respectively.