Effect of nitrogen doping on the structural and the optical variations of graphene quantum dots by using hydrazine treatment

Graphene quantum dots (GQDs) have been prepared by hydrothermal cutting of graphene sheets and subsequently doped with N atoms by using hydrazine treatment to study the effect of doping on the structural and the optical properties of the GQDs. The pyridinic N atoms, which were increased in number by hydrazine treatment, are bonded with C atoms at the edge of the GQDs, thereby making the GQDs not only larger but also n-type conductive with a concomitant reduction of the edge-related defects. The absorption band of GQDs is peaked at ~300 nm, and after doping, they show an additional absorption peak at ~354 nm, which originates from the impurity energy level formed by the N doping. The GQDs emit bright blue photoluminescence (PL) peaked at 418 nm, and after hydrazine treatment, the PL emission is redshifted by ~15 nm and its decay becomes slower, resulting from the N-related impurity level.