Fluorescence Tuning of Carbon Dots from Red to Blue via UV‐Induced Photochemical Etching

Carbon dots (CDs) have attracted extensive interest owing to their outstanding optical properties, biocompatibility, and low-cost synthesis. Nevertheless, the preparation of multicolor CDs remains complex and most post-synthetic strategies allow only limited wavelength modulation, the full-spectrum tunability across the visible region still has yet to be achieved. Herein, we report a simple photochemical strategy that enables continuous fluorescence tuning of red-emissive CDs (R-CDs) via controlled UV-induced photoetching in N,N-dimethylformamide. UV irradiation generates reactive radical species, which progressively disrupt graphitic domains. Meanwhile, solvent-surface interactions synchronously regulate emissive surface states, and the two effects together enable precise size control and continuous emission modulation. Consequently, the emission peak of the R-CDs exhibits a systematic blue shift from 657 nm to 573, 530, 490, and ultimately 443 nm, achieving full-spectrum emission across the visible range. Notably, irradiation time serves as a single adjustable parameter, greatly simplifying the optimization of multiple synthetic conditions. Beyond their excellent performance in high-color-rendering-index white light-emitting diodes, the photochromic CDs were further applied in multi-level fluorescent information encryption, achieving five distinct levels of optical security. This work establishes a robust platform for progressive fluorescence tuning of CDs with promising potential in advanced photonic and information-security applications.