Hydrothermal synthesis and photoluminescent mechanistic investigation of highly fluorescent nitrogen doped carbon dots from amino acids

A green and facile method was developed to synthesize nitrogen doped carbon dots (NCDs) with blue-luminescence by hydrothermal treatment of different amino acids (aspartic acid, glutamic, proline, threonine, valine, phenylalanine, arginine and serine). The NCDs were characterized by various methods and the highest quantum yield reached 41.3%. The formation and surface passivation of NCDs were accomplished simultaneously via dehydration, polymerization, carbonization, and passivation process. The passivation degree of NCDs was controlled by the hydrothermal time. NCDs had good aqueous dispersibility, high stability, and preeminent photoluminescent properties. The emission of NCDs was highly dependent on excitation energy, as the excitation wavelength increased from 300 to 470 nm, the emission peak position shifted from blue to green region with the intensity decreased. These features resulted from the fact that the surface passivation could form the additional interband and we explained the relationship between luminescent properties and energy band in detail.