Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Department Online Seminar
Chair: Sebastian Mährlein

Monday, December 13, 2021, 3:00 pm
Dr. Joanna Urban
École Normale Supérieure Paris-Saclay
Department Online Seminar - Excitons and Lattice Dynamics in Novel Semiconductor Materials Probed by Optical Spectroscopy
2D layered semiconductors are both a fascinating platform to investigate quantum and dielectric confinement phenomena and versatile candidates for optoelectronic applications. Hybrid 2D layered perovskites combine large exciton binding energies with unique properties related to the dynamics of their soft, polar lattice.
I will start by presenting my work on a class of layered vdW materials which share an interesting additional degree of freedom: in-plane anisotropy [1,2,3]. In the second part of the talk, I will focus on our study of the exciton-phonon coupling in quasi-2D Ruddlesden-Popper perovskites. Based on measurements in high magnetic fields we show that excitons hosted in the inorganic lattice can couple to vibrational modes related to the motion of the organic ligands. We attribute the complex spectral shape - which is the subject of ongoing controversy - to a vibronic progression [4]. Finally, I will discuss our recent investigations of defect-related photoluminescence in the archetypal 3D perovskite MAPbI3. At 4 K, in addition to DAP and bound exciton emission, we observe sharp (<100-300 μeV) peaks which show intense spectral diffusion and originate from highly localized zones. Our study extends recent similar findings in microcrystalline all-inorganic CsPbBr3 [5] and we propose the observed spectral features originate at lattice defects or low potential-energy nanodomains within the bulk crystal.
[1] J. Urban et al., Nanoscale, 9 (2017)
[2] J. Urban et al, 2D Mater. 6 (2019)
[3] R. Frisenda et al., Nano Lett. 20, (2020), 2
[4] J. Urban et al., Phys. Chem. Lett. 2020, 11, 15
[5] S. Feng, Adv. Mater. (2021), 2106278

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