Carbon dots (CDs), a versatile class of fluorescent carbon-based nanomaterials, have attracted widespread attention due to their exceptional optical properties, biocompatibility, and cost-effectiveness. Their applications span biomedicine, optoelectronics, and smart food packaging, yet large-scale synthesis remains a significant challenge. This review categorizes large-scale synthesis methods into liquid-phase (hydrothermal/solvothermal, microwave-assisted, magnetic hyperthermia, aldol condensation polymerization), gas-phase (plasma synthesis), solid-phase (pyrolysis, oxidation/carbonization, ball milling), and emerging techniques (microfluidic, ultrasonic, molten-salt). Notably, microwave-assisted and solid-state synthesis methods show promise for industrial production due to their scalability and efficiency. Despite these advances, challenges persist in optimizing synthesis reproducibility, reducing energy consumption, and developing purification methods and quality control strategies. Addressing these issues will be critical for transitioning CDs from laboratory research to real-world applications.

Carbon dots (CDs), especially multicolor carbon dots, have tremendous potential applications in light-emitting diodes, photocatalysis, bioimaging and sensing; however, the production of carbon dots with multicolor emissions involving tunable PL (photo-luminescence) from blue to red is still difficult. Here, we proposed solvent-controlled and solvent-dependent strategies to obtain multicolor carbon dots via adjusting the graphitization degree and surface functional groups. Blue and red carbon dots were successfully prepared by the hydrothermal method using p-phenylenediamine and oxalic acid. By simply varying the solvent in the reaction, the fluorescence emissions of CDs notably shifted from blue to red. More importantly, it was demonstrated that r-CDs (red CDs) can produce different independent long-wavelength fluorescence emissions ranging from green to red by dispersing CDs into different solvents. Moreover, the as-prepared r-CDs exhibited a response to the changes in pH values and showed apparent color changes from reddish brown to light purple visible to the naked eye in daylight. With low cytotoxicity and tunable emissions, our CDs show potential in solvent sensing, pH sensing and bio-labeling.

Transforming carbon dots (CDs) fluorescent materials into smart materials with complex functions is a topic of great interest to nanoscience. However, designing CDs with regulating fluorescence/phosphorescence that can be visually monitored with the environment changes in real‐time remains a challenge. Here, a very simple strategy, one‐step solvent‐free catalytic assistant strategy, which is low cost, facile, environment‐friendly, and high throughput, is put forward. Hydrogen bond is used to manipulate nanostructure of CDs, and the obtained carbon dots (M‐CDs) show a series of attractive properties including matrix‐free room‐temperature phosphorescence, time‐dependent fluorescence, and near‐infrared emissive characteristics. Different from the traditional aggregation caused quenching or aggregation‐induced emission fluorescent materials, M‐CDs exhibit unprecedented and unique dispersion induced redshift fluorescence phenomenon, promoting the studies of fluorescence from static to dynamic. The causes of this phenomenon are further analyzed in detail. As a kind of intelligent fluorescent materials, this new designed CDs greatly enrich the basic recognition of CDs by illustrating the relationship between redshift fluorescence behaviors and the dispersion states, and may provide with an opportunity for solid‐state fluorescent materials, anti‐counterfeiting, cellular imaging, and hopefully many others.