On the origin and tunability of blue and green photoluminescence from chemically derived graphene: Hydrogenation and oxygenation studies

We report on the identification of structural defects and oxygenated functional groups responsible for blue and green photoluminescence (PL) from the chemically derived graphene (CDG) thin films with the help of Raman imaging/spectroscopy, high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR) and PL analyses. In particular, we probe the role of in-plane and edge oxygenated functionalities on the evolution of visible PL emissions from CDGs after controlled hydrogenation and oxygenation studies. The assignments of the various PL bands were corroborated from thermogravimetric and FTIR analyses in the CDGs and are directly correlated with the Raman analysis. Our studies reveal that the PL emission spectrum in CDGs can be tuned by controlled hydrogen and oxygen treatments. Two green emission bands in the range of ∼497-502 nm and ∼534-551 nm are assigned to the COOH and CO sub-band energy states belonging to the edge sites, while the blue emission is attributed to the localised states of sp2/sp3 domains and epoxy related in-plane functional groups in the CDG materials. Our study demonstrates the tunability of PL spectrum from CDG materials through selective manipulation of the functional groups at the in-plane defects and edge sites.