Carbonized polymer dots (CPDs) have received tremendous attention during the last decade due to their excellent fluorescent properties and catalytic performance. Doping CPDs with transition metal atoms accelerates the local electron flow in CPDs and improves the fluorescent properties and catalytic performance of the CPDs. However, the binding sites and the formation mechanisms of the transition‐metal‐atom‐doped CPDs remain inconclusive. In this work, Mn2+‐ion–doped CPDs (Mn‐CPDs) are synthesized by the hydrothermal method. The Mn2+ ions form MnO bonds that bridge the sp2 domains of carbon cores and increases the effective sp2 domains in the Mn‐CPDs, which redshifts the fluorescence emission peak of the Mn‐CPDs slightly. The Mn2+ ions form covalent bonds in the CPDs and remedy the oxygen vacancies of the CPDs, which cuts off the non‐radiative–recombination process of the Mn‐CPDs and increases the quantum yield of the Mn‐CPDs to 70%. Furthermore, the MnO bonds accelerate the electron flow between adjacent sp2 domains and enhances the electron transport in the Mn‐CPDs. Thus, the Mn‐CPDs demonstrate excellent catalytic performance to activate hydrogen peroxide (H2O2) and produce hydroxyl radicals (•OH) to degrade methylene blue (MB) and rhodamine B (RhB).

The preparation of multicolor and white light-emitting carbon dots (CDs) is of both significant importance and challenging for their applications as white phosphors for light-emitting diodes (LEDs). In this report, a facile reaction system that is capable of preparing both multicolor and white light-emitting CDs was disclosed. In this system, three CDs emitting yellow, red, and green lights were prepared, and monochromatic LEDs were constructed using these multicolor CDs. Most importantly, single-component white light-emitting CDs with CIE coordinates of (0.33, 0.33) were also prepared. The white light-emitting CDs were applied as single-component white phosphors for the fabrication of white LEDs. The white LEDs constructed demonstrated excellent performance, emitting warm white light (CCT = 3723 K) with CIE coordinates of (0.39, 0.37) and an extremely high color-rendering index of 91.5, which should find favorable applications for indoor illumination.

The development of red emission carbon dots with bright solid-state fluorescence would significantly broaden their application in optoelectronic devices and sensors. Herein, a red-emissive carbon dot-based nanocomposite has been synthesized through chemical bonding with cellulose films. The red emission originating from the surface states of carbon dots was maintained in the cellulose films. Due to the stable chemical bonding, the photoluminescence intensity and emission wavelength remained unchanged for 12 months, and the quantum yield of the composite was enhanced over 4 times. It also showed outstanding stability in water or weak acid–base environments under pHs ranging from 2 to 11. Therefore, the mechanism of chemical bonding that eliminated the defects and preserved the efficient radiative process through surface states was proposed.

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