Solid-State Emissive Carbon Quantum Dots (CQDs) with a Long Wavelength Emission

Abstract

Carbon quantum dots (CQDs)—growing stars of the nanocarbon family—have received attention owing to their intriguing photoluminescence (PL), stability, and biocompatibility. However, CQDs may suffer from serious aggregation-caused quenching (ACQ) of PL, specifically in powder or thin film form. Moreover, most engineering applications are solid-state; therefore, it is important to design solid-state emissive CQDs, potentially defeating ACQ. Previous reviews highlighted the strategies for solid-state emissive CQDs; however, less focus has been given to CQDs with emissions at longer wavelengths. This review summarizes recent advances (specifically in the last two years), focusing on long wavelengths, including yellow-, orange-, and red-emissive fluorescence. Furthermore, the synthesis method, quantum yield, and mechanism of fluorescence are explained. In addition, a detailed summary of synthesis parameters and their role in emission tuning is highlighted. Finally, the future directions and potential applications of solid-state CQDs for emerging applications were discussed.