麻豆淫院

Semiconductor nanocrystals (NCs) hold great promise as sensitizers for triplet-triplet annihilation up-conversion (TTA-UC) due to their facile bandgap tunability and negligible inter-system crossing loss. However, the understanding of the correlation between bright/dark exciton and triplet energy transfer (TET) is still lacking. More research on this is strongly needed to reveal the distinctions between NCs-sensitized and molecular-sensitized TTA-UC, which is important to further tailor and enhance the NCs-sensitized TTA-UC.

In a study published in Laser and Photonics Reviews, the research group led by Prof. Zhu Haomiao from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences used 1-naphthoic acid (1-NA, mediator) decorated 2 nm thick CsPbBr₃ nanoplates (NPls) as the model system to explore the respective contribution of bright/dark exciton to TET.

The researchers found that the well-characterized and unique exciton fine structure and large bright-dark exciton splitting energy of CsPbBr₃ NPls offer an ideal platform to unambiguously resolve the role of dark exciton in TET.

Due to the large bright-dark exciton splitting energy, the dark exciton will be majorly populated at low temperature. By monitoring the exciton decay dynamic at cryogenic temperature with the presence of mediator, the researchers revealed that the singlet dark exciton is the major energy source for TET.

The researchers also explained the efficient TET between dark singlet exciton and mediator by considering the ill-defined nature of exciton spin state. In CsPbBr₃ NPls, the strong orbit-spin coupling of conduction band electron mixes the triplet and singlet states, which makes TET between singlet dark exciton and triplet state of mediator possible. In addition, the long intrinsic lifetime of dark exciton greatly facilitates the TET.

Besides, by combining 1-NA decorated CsPbBr₃ NPls with 2,5-diphenyloxazole (PPO), the researchers achieved an efficient visible-to-ultraviolet upconversion from 450 nm to 355 nm. In this system, the excitation threshold is only 0.79 W/cm² which is more than two times lower than that of using conventional CsPbBr₃ nanocrystals as the sensitizer.

This study sheds a new light on NPls sensitized TET and efficient visible-to-ultraviolet TTA-UC, which can substantially extend the working spectrum of TiO₂ or NiO based photo-catalysis.