Abstract
Highly fluorescent N-doped graphene quantum dots (NGQDs) and graphitic carbon nitride quantum dots (CNQDs, g-C3N4) were synthesized using a solid-phase microwave-assisted (SPMA) technique. The SPMA method, based on the pyrolysis of citric acid and urea with different recipes, is capable of producing quantum dots with coexisting NGQDs and CNQDs at 280°C within only five minutes. The photoluminescence (PL) emissions from NGQD and CNQDs are strongly dependent on excitation wavelength and the solvent type, i.e., water, ethanol, and N-methyl pyrrolidinone. The unique design of the quantum dots possesses a multiple chromophoric band-gap structure, originated from the presence of g-C3N4, defect-related emissive traps, and grain boundaries. Thus, an appropriate excitation wavelength induces a conjugated π electron system to fulfill the most probable absorption band, resulting in wavelength-dependent emissions including ultraviolet, visible and infrared light. The quantum yield of the NGQD and CNQD samples can attain as high as 68.1%. Accordingly, one light-emitting device using the combination of the NGQD and CNQD powders embedded polymeric film can emit white-like light with high power conversion efficiency.
