Optical Properties of Carbon Dots: A Review

Abstract

Fluorescent carbon dots (CDs) have attracted increasing attention in recent years owing to their most significant advantages in terms of low toxicity, resistance to photobleaching, small size, easy functionalization, eco-friendly synthesis and diverse imaging capabilities. However, the unclear optical mechanism of CDs greatly limits their further application. Understanding the optical property of CDs is of great significance for controllable development of top-designed CDs with functional purposes. In this review, we firstly summarize that light absorption properties of CDs, and demonstrate the relationship between the absorption spectrum and electron transition of both the core and shell of CDs. Furthermore, we summarize the common fluorescent mechanisms of CDs, including surface state, quantum confinement effect, conjugated structures, self-trapped excitons, edge defects, free zigzag sites, and multi-emissive centers. Finally, we also discuss the phosphorescence properties of CDs. This review gives new insights into how to tune the fluorescence and phosphorescence of the CDs.