Sunlight‐Activated Room‐Temperature Phosphorescent Carbon Dots

Abstract The efficient utilization of clean and safe sunlight as an excitation source for room‐temperature phosphorescent (RTP) materials is crucial for practical applications in solar energy. Herein, sunlight‐activated RTP nitrogen‐doped carbon dots @ alumina (N‐CDs@Al 2 O 3 ) composites with long lifetime and exceptional stability are designed and fabricated using an in situ preparation strategy. The N‐CDs@Al 2 O 3 display bright yellow RTP (more than 18 s to the naked eye) when activated by sunlight. The results indicate that the introduction of nitrogen into the CDs not only promotes the effective filling of triplet excitons but also facilitates the red‐shift of the absorption spectrum of the CDs. The high rigidity structure of Al 2 O 3 and stable strong covalent bonds effectively protect the triplet excitons. Additionally, the numerous oxygen vacancy defects formed under appropriate calcination conditions effectively store and release triplet excitons. Finally, the application of N‐CDs@Al 2 O 3 in multi‐color 3D artworks, defense markings, and emergency signs is demonstrated. This work provides design principles and feasible strategies for the development of new sunlight‐activated RTP materials.