Effects of chemical bonds between nitrogen and its neighbor carbon atoms on fluorescence properties of carbon quantum dots

Abstract

The nitrogen atoms have been attracting enormous attention in improving the fluorescent properties of carbon quantum dots (CQDs), but the contribution varies widely. In this work, the effects of chemical bonds between nitrogen and its neighbor carbon atoms as well as the nitrogen/carbon molar ratio (N/C) on fluorescence properties of CQDs were investigated. Importantly, the former was disclosed based on two kinds of well-designed nitrogen doped CQDs (N-CQDs-1 and N-CQDs-2) that show differences in chemical bonds of doped nitrogen atoms but contain the same N/C ratio and are common in the content of sp2 hybridized carbon atoms and particle size. We concluded that pyridine N rather than pyrrole N is beneficial to increasing the emission intensity of CQDs, probably caused by the enhancement of electron exchange of complex luminescent centers, and the formation and introduction of electron traps. And the emission intensity does increase with the amount of doped nitrogen atoms. Therefore, the N-CQDs-1 containing the most amount of N atoms as forms of pyridine and pyrrole shows amazing fluorescent properties and highly quantum yield (QY) up to 34.23%.