Solid-state fluorescent carbon dots: quenching resistance strategies, high quantum efficiency control, multicolor tuning, and applications

As a new member of the carbon family, carbon dots (CDs) not only inherit the advantages of good biocompatibility and abundant raw material sources from traditional carbon materials, but also exhibit outstanding luminescence characteristics, such as tunable emissive wavelength and light bleaching resistance. Thus, they show great application prospects in many fields. However, CDs may suffer from serious aggregation-induced fluorescence quenching and lack of high quantum efficiency and tunable full color solid-state fluorescence, which hinder their large-scale application. In this review, the recent advances in the solid-state fluorescence properties of CDs are summarized, with special emphasis on the strategies for quenching resistance, methods for high quantum efficiency, and methods for multicolor tuning. The strategies for obtaining quenching-resistant CDs include the dispersion of CDs in situ and post processing, and the preparation of CDs with uniform structure. Solid-state fluorescent CDs with high quantum efficiency can be obtained by controlling the matrix type and CD concentration, doping heteroatoms, and adding salt crystals in situ and reducing the carbonization degree. Solid-state multi-color CDs are realized using three methods, including the effective dispersion of multicolor CDs, gradient concentration dispersion of concentration-induced multicolor emissive CDs and fluorescence origin ( i.e. , core size, surface states and molecular states) tuning of self-quenching-resistant CDs. The applications of solid-state fluorescent CDs in fingerprint identification, photoelectric device and visible light communication are also outlined. Finally, their challenges and prospects in the future are presented. In this review, comprehensive overview about solid-state fluorescent CDs is given, with especial emphasis on the strategies for quenching-resistance, the methods for high quantum efficiency, the methods for multicolor tuning and their application.