Metal and non-metal doped carbon dots: properties and applications

Carbon dots (CDs) have shown great potential for application in optoelectronics, owing to their merits of tunable fluorescence, biocompatibility, low toxicity, and solution processability. However, the intrinsic nature of CDs makes them prone to fluorescence quenching in the aggregated state. In addition, the emission peak width at half maximum of a single CD is usually greater than 60 nm, and the emission spectra may exhibit a multi-peak superposition state, resulting in poor monochromaticity. Further, the unsatisfactory quantum yield of CDs restricts their further application. Considering this, doping strategies have successfully improved the electrical, optical, and chemical properties of CDs. The intrinsic structure and electron distribution of CDs can be effectively adjusted by metal or nonmetal doping. Doping atoms generate n- or p-type charge carriers, changing the bandgap energy, and thereby improving the photophysical properties of the CDs. In this comprehensive review, we explore the intricate effects of various doping strategies on CDs and systematically categorize them. Notably, we elaborate on the diverse types of doped CDs and emphasize their photophysical properties, aiming to elucidate the fundamental mechanisms underlying the influence of doping on CD performance. Specifically, this review describes the extensive applications of doped carbon dots (X-CDs) in optoelectronic devices, information encryption, anti-counterfeiting measures, imaging techniques, and detection fields, to spur further X-CD exploration and application.