Aggregation-induced band gap narrowing in N- doped carbon dots: concentration-dependent energy level redistribution...

A new strategy for preparing nitrogen-doped carbon quantum dots (N-CQDs) with emission in the full visible range (448-628 nm) is achieved solely through concentration modulation, bypassing complex synthesis or external stimuli. The results showed that the intensities of C = O and C = N in N-CQDs differed at different concentrations, suggesting that the concentration change may cause the alteration of intermolecular interactions, which in turn affects their surface states. Structural analyses and theoretical calculations revealed that as the concentration of N-CQDs increased, their aggregation led to a steady reduction in the band gap, ranging from 3.27 to 2.30 eV. Furthermore, N-CQDs can be applied to Fe(III) detection and multicolor cell imaging. In addition an aggregation-induced multicolor emission mechanism of N-CQDs is proposed, which provides an important scientific basis for the development of novel multicolor optical materials and the expansion of their potential applications.