Multilevel Stimulus‐Responsive Room Temperature Phosphorescence Achieved by Efficient Energy Transfer from Triplet Excitons to Mn²⁺ Pairs in 2D Hybrid Metal Halide

Abstract Synthesis of color‐tunable ultralong room temperature phosphorescence (RTP) crystals with multilevel stimuli‐responsive properties is highly desirable due to their tremendous application prospects but has rarely been explored. Herein, a 2D organic–inorganic metal‐halide hybrid (ABA₂CdCl₄) has been originally designed and synthesized with efficient blue fluorescence and green RTP through Cd induced heavy atom effect. Due to the improved intermolecular interactions and enhanced light absorption, a high RTP efficiency up to 34% is achieved in ABA₂CdCl_4. With ABA₂CdCl₄ as a prototype, Mn²⁺‐doping strategy is successfully employed to construct multicomponent RTP material with wide‐tunable RTP property in response to multilevel external stimulus such as time, temperature and light. More importantly, Mn²⁺ pairs are formed in Mn²⁺‐doped ABA₂CdCl₄, which are observed in 2D metal‐halide hybrids for the first time. Due to the thermal assisted energy transfer from triplet excitons (organic unit) to Mn²⁺ pairs, and the thermally activated emission from Mn²⁺ pairs, tunable RTP colors between 270 and 333 K are easily realized, showing the highest sensitivity against temperature reported so far. By virtue of the above advantages, such materials are successfully applied in multilevel information storage and temperature sensors. The work promotes the development of multi‐stimuli responsive RTP systems based on hybrid metal halides.