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.