Near-Infrared Carbon Dots: From Precursors and Synthesis to Luminescence Mechanisms and Multifunctional Applications.

Carbon dots (CDs) are emerging zero-dimensional carbon-based nanomaterials with unique optical properties. Among them, near-infrared carbon dots (NIR-CDs), exhibiting absorption/emission in the biological transparency window (650-1700 nm), have attracted increasing attention due to their excellent biocompatibility, high spatial resolution, and low photo-toxicity. In this review, we systematically summarize the development of NIR-CDs including preparation methods, rational design and choice of precursors, optical characteristics and mechanisms, and multifunctional applications. A comprehensive and detailed methodological description encompassing the synthesis strategies, rational design, and precursor engineering of NIR-CDs are provided. And then the optical properties of NIR-CDs, including absorption, fluorescence, phosphorescence, nonlinear optical properties, and their mechanisms are further discussed and analyzed. Finally, recent advances in the multifunctional applications of NIR-CDs are summarized, covering light-emitting devices, fluorescence sensing, environmental, hydrogen energy, and biomedical fields. By consolidating current knowledge into a unified framework and identifying key challenges and opportunities, the review not only offers the most up-to-date and holistic perspective on NIR-CDs but also serves as a guide to accelerate the translation of NIR-CDs from laboratory research to practical applications.