Origin of Modified Luminescence Response in Reduced Graphitic Carbon Nitride Nanosheets

We report on the tuning of luminescence response of few layered graphitic carbon nitride (g-C3N4) nanosheets by reducing the functional groups though chemical reduction. The nanosheets of g-C3N4 have been obtained from its bulk counterpart through liquid phase exfoliation, while the attached functional groups have been removed through sodium borohydride treatment. X-ray photoelectron and micro Raman studies indicate the improved aromatization through the removal of the functional groups, while structural defect formation has been realized at higher reduction levels. It has been found that the increase in sp(2) C-N cluster size as a result of improved aromatization leads to the enhanced absorption through pi -> pi* transition. Consequently, the luminescence response has been found to increase at the lower reduction level. On the other hand, near-ultraviolet emission and suppressed visible emission has been witnessed at higher reduction levels. The improvement in near-ultraviolet emission originates from the modified density of states which favors the transitions involving delta* and N lone pair states. Better understanding of the reduction mechanism can lead to the fabrication of prototype flexible light emitting devices that can emit light in the ultraviolet as well as the visible region of the spectrum.