Semiconductor photocatalysts have recently received growing attention, but still meet the challenges of a weak separation ability of photogenerated electrons and holes, which leads to energy loss. In this work, we utilize ultralong-lived triplet excitons to promote the separation of electron-hole pairs and to realize the efficient transformation from excitons to carriers. Room temperature phosphorescent (RTP) carbon dots (CDs) were selected as a model system, which were highly dispersed onto g-C 3 N 4 and exhibited largely enhanced photocatalytic and electrochemical activities compared with those of typical fluorescent CD systems. Both experimental and density functional theory calculations show that the ultralong-lived triplet excitons from RTP CD@g-C 3 N 4 serve as an “energy sustained-release capsule” and thus effectively regulate the recombination of excitons and boost the intrinsic photocatalytic performances (including water splitting and dye degradation). Therefore, this work provides a new design strategy to use ultralong-lived triplet excitons as high-efficiency photocatalysts.