Phosphorescent Carbon Dots Confined in Al ₂ O ₃ With Broad Excitation Range

Developing single‐component carbon dot (CD)‐based composites with long‐lived emission, tunable colors, and broad excitation range remains scientifically challenging. Herein, CDs and alumina composites (CDs@Al 2 O 3 ) with broad excitation range were synthesized through a one‐step calcination method using benzamide as the carbon source. The room temperature phosphorescence (RTP) emission color shifts from blue to green to yellow as excitation wavelength increases. CDs@Al 2 O 3 synthesized at an optimized calcination temperature of 500°C exhibits lifetimes of up to 1.36 s under 258 nm excitation and 0.63 s at 520 nm. Photophysical analysis reveals that the multicolor afterglow originates from multiple emission centers within the CDs. N, O co‐doping creates novel surface states, while the rigid matrix confines emission centers, suppressing non‐radiative decay and enabling phosphorescence tuning. CDs@Al 2 O 3 demonstrates potential in anti‐counterfeiting and information encryption due to its unique optical properties. This work provides a novel strategy for designing single‐component optical materials with color‐tunable emission and broad excitation range.