Doping of a heteroatom such as nitrogen in carbon nanomaterials provides a means to tailor their electronic properties and chemical reactivities. In this article, we present simple methods to synthesize carbon quantum dots (CQDs) with high nitrogen doping content (18–22%), involving the reaction of glucose in the presence of urea under hydrothermal conditions or by microwave irradiation. The N-doped carbon quantum dots (N-CQDs) show high aqueous solubility and tunable photoluminescence (PL). Interaction of N-CQDs with exfoliated graphene or dimethylaniline quenches PL. Interaction of N-doped as well as undoped C-dots with electron-donating tetrathiafulvalene and electron-withdrawing tetracyanoethylene has been examined. The intense blue PL of CQDs has been exploited to produce white light by mixing the CQDs with yellow light emitting ZnO nanoparticles or graphene oxide. The N-doped CQDs exhibit superior photocatalytic activity compared to pristine CQDs.