Magneto-Optical Functionality and Energy Transfer in Metal-Halide Perovskite Nanocrystals Doped with Transition Metals

• Applicant: Professor Dr. Gerd Bacher
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410410899

The overall goal of this project is to investigate the magneto-optical functionality and the energy transfer of perovskite nanocrystals doped with transition metals (TM, mainly Mn). The specific crystal structure of lead halide perovskites (APbX3, A = Cs, MA, FA; X = Cl, Br, I) is expected to allow for incorporation of TM2+ cations on six-fold coordinated lattice sites (replacing Pb2+) – in contrast to the more 'traditional' case of TM doping of II-VI chalocogenides, where the dopants are usually incorporated on four-fold coordinated sites. The uniqueness of these materials relies in addition on the different bandstructure (conduction band formed by p-states, valence band by s-states) and the more ionic bonds as compared to II-VI nanocrystals. Moreover, crystal phase transitions from the cubic to the tetragonal and finally the orthorhombic phase occur when lowering the temperature. In spite of several reports on Mn2+ doped APbX3 nanocrystals in literature there is no proof of any giant magneto-optical functionality caused by sp-d exchange interaction up to now. We intend to use magnetic circular dichroism measurements and magneto-photoluminescence experiments over a wide range of temperatures to investigate whether giant sp-d exchange effects are present in this novel material class, where the hybridization of the orbitals might significantly differ from II-VI nanocrystals due to the differently coordinated sites of the dopants and the more ionic bonds. In addition lead halide perovskites undergo a specific crystal phase transition when reducing the temperature leading to a discontinuous change of the emission energy. It is planned to investigate how this crystal phase transition affects the energy transfer from band states to luminescent dopants (and back), and whether this effect can be used for realizing dual emitters with two distinct critical temperatures by carefully adjusting the bandgap, e.g. by the Br/I ratio or the nanocrystal size, with respect to the internal 4T1 – 6A1 transition of the Mn2+ dopant.

• DFG Programme: Research Grants