▎ 摘　　要

In this study, N-doped graphene oxide (N-GO) and graphene quantum dots (N-GQDs) were synthesized by the carbonization of branched polyethyleneimine (PEI) in the presence of H2O2. The prepared N-GO has plenty of small sp(2) clusters, which are non-uniform in size and poorly passivated, leading to a weak and an excitation-dependent photoluminescent (PL) performance. Whereas N-GQDs exhibit a strong and excitation-independent PL property because of the sp(2) clusters uniform in size and well passivated by the partially carbonized PEI. Furthermore, the obtained N-GQDs show little cytotoxicity and promise in Pb2+ recognition as well as cell imaging.