Visible‐Light‐Excited Ultralong‐Lifetime Room Temperature Phosphorescence Based on Nitrogen‐Doped Carbon Dots for Double Anticounterfeiting

Abstract Visible light is ubiquitous and safer than ultraviolet light; however, synthesizing ultralong‐lifetime room temperature phosphorescent (URTP) carbon dots (CDs) with visible‐light excitation remains a formidable challenge. Herein, an easy and fast method for synthesizing visible‐light‐excited URTP CDs is devised. The synthesized CDs have URTP lifetime of 1.51 s which is a relatively long life RTP lifetime ever reported. Furthermore, it is revealed that the dense core of CDs, the formation of long‐chain polymers on the surface, and the presence of hydrogen bond skeleton play a crucial role in the production of URTP. Also, the introduction of the N element is a critical factor in the URTP synthesis as it promotes the n–π* transition and facilitates intersystem crossing (ISC) such that the triplet state is filled with effective excitons. Notably, the CDs demonstrate URTP properties under the excitation of 365 UV light and exhibit URTP under the excitation of visible light. This is a rare report of visible‐light‐excited URTP based on CDs. Considering this excellent property, URTP CDs may be applied in the field of anticounterfeiting. These findings may broaden the path for the development of visible‐light‐excited URTP materials and their applications.