Long-wavelength, multicolor, and white-light emitting carbon-based dots: Achievements made, challenges remaining, and applications

Abstract The use of carbon-based dots (C-bDs), involving carbon dots, carbon quantum dots, and graphene quantum dots, as a new class of photoluminescent nanomaterials is rapidly expanding. Their many advantages including water solubility, high stability, low toxicity, ease of functionalization, and cost-efficient and simple synthetic routes have introduced them as potential alternatives to conventional semiconductor-based quantum dots. However, difficulty in preparing long-wavelength and multicolor-emitting C-bDs has caused some major disadvantages for these nanomaterials and limited their application in fields such as bioimaging and multicolor patterning. Although different emission colors from C-bDs can be observed by varying their excitation wavelength, this is not identified as real photoluminescence tuning, and in fact, preparing C-bDs with such special photoluminescence properties has proven to be a challenging task. This review summarizes to date successes in preparing long-wavelength, multicolor, and white-light-emitting C-bDs along with their potential applications. We discuss the developments in using specific precursors, synthetic methods, heteroatom doping, and post treatments such as separation and surface modification methods that have led to C-bDs with unique emission colors.