Concentration‐Dependent Photoluminescence Properties of Graphene Oxide

Herein, a comprehensive examination of the effect of concentration on graphene oxide (GO) photoluminescence (PL) is presented. It is found that GO exhibits a concentration‐induced redshift and white light PL for GO aqueous dispersions, and displays visible–NIR PL for a 3D GO foam (3DGOF) corresponding to the high‐concentration‐limit of GO. It is deduced that the effect of the coupling between the GO sheets gives rise to the observed redshift, and hopping and tunneling effects result in the saturation of the PL redshift and then the PL quenching. Due to the intense interactions and coupling of the GO sheets, the modification of the GO surface state increases the energy of the π* state and/or makes the high‐energy level appear and therefore gives rise to the blue light component. Consequently, high concentrations of GO aqueous dispersion lead to the appearance of combined white light. For 3DGOF, electron–hole radiation recombination in laser‐induced plasma and GO bandgap may be responsible for the observed visible–NIR PL. Based on its tunable PL in the visible–NIR region of the spectrum and the induced white light PL, GO has huge potential for applications in graphene‐based optoelectronics and biomedicine