Doping-engineered room-temperature phosphorescent carbon dots: Mechanisms, strategies, and applications

Room-temperature phosphorescent carbon dots (RTP CDs) show great promise for applications in information security, data encryption, optoelectronic devices, and biomedicine, due to their long lifetime triplet-state emission, high signal-to-noise ratio, and excellent photostability. However, the intrinsic spin-forbidden nature of CDs restricts intersystem crossing (ISC) process, resulting in a low yield of triplet excitons. Furthermore, triplet excitons are prone to deactivation via nonradiative transitions, which significantly shortens the phosphorescence lifetime. Among various regulation strategies, heteroatom doping has proven to be an effective approach for significantly enhancing the RTP emission of CDs, as it can modulate the electronic structure and energy level distribution of CDs, strengthen spin-orbit coupling to promote ISC, and construct a rigid microenvironment to stabilize triplet excitons. In this review, we provide a comprehensive examination of how nonmetal, metal, and co-doping strategies regulate the RTP performance of CDs, focusing on the luminescence mechanisms, synthetic approaches, and performance modulation of RTP doped CDs (D-CDs), and further discusses their potential applications in information security, optical devices, sensing, and biomedicine. Finally, current challenges and future development directions for RTP D-CDs are presented, aiming to offer theoretical and practical guidance for the rational design and application expansion of high-performance RTP CDs.