Steering Energy Transfer Pathways through Mn-Doping in Perovskite Nanocrystals

Modulation of singlet and triplet energy transfer from excited semiconductor nanocrystals to attached dye molecules remains an important criterion for the design of light-harvesting assemblies. Whereas one can consider the selection of donor and acceptor with favorable energetics, spectral overlap, and kinetics of energy transfer as a means to direct the singlet and triplet energy transfer pathways, it is not obvious how to control the singlet and triplet characteristics of the donor semiconductor nanocrystal itself. By doping CsPb(Cl_0.7Br_0.3)₃ nanocrystals with Mn²⁺, we have now succeeded in increasing the triplet characteristics of semiconductor nanocrystals. The singlet and triplet energy transfer between excited Mn-CsPb(Cl_0.7Br_0.3)₃ nanocrystals and a cyanine dye (4,5-benzoindotricarbocyanine) show the participation of band gap states in singlet energy transfer and Mn²⁺-activated states in triplet energy transfer. By tracking donor and acceptor emission as well as transient absorption spectral features, we were able to distinguish the two independent energy transfer pathways. Whereas singlet energy transfer from the exciton emission band remains unchanged (2%), increasing the concentration of Mn²⁺ in perovskite nanocrystals results in an increase of triplet energy transfer yield up to 17.5%. The ability to enhance the triplet transfer yield in CsPb(Cl_0.7Br_0.3)₃ nanocrystals through Mn-doping opens up new opportunities to develop optoelectronic and display devices.