Title: Spin-dependent Exciton dynamics in Colloidal Perovskite Nanocrystals
Speaker: Dr. Amrita Dey, Ludwig-Maximilian University, Germany
Abstract: Metal halide perovskite nanocrystals (PNCs) are gaining increased attention in the field of optoelectronics owing to their plethora of novel properties and have emerged as a new class of semiconductor light sources. Despite many recent studies focused on the energetic carrier relaxation dynamics in PNCs, their spin-dependent exciton kinetics has not been explored yet. In general, spin of exciton plays an important role in controlling the optical transitions of semiconductor nanocrystals due to the intimate connection between spin and optical polarization. The aim of my research is to understand the fundamental spin-polarized optical properties in colloidal PNCs. We have found out that in CsPbX 3 (X=I, Br) NCs spin- polarization of the photo-excited carriers diminishes quickly while excited far from the optical band edge. Besides exciton-phonon coupling controls the spin-transitions of the optically excited electrons and holes. Unlike CsPbBr 3 NCs, optical band edge of lead free indirect gap Cs 2 AgBiBr 6 double perovskite NCs are dominated by resonantly pronounced optical transition. We conclude that this optical transition is due to defect related bound excitons. This direct bound exciton causes a high energetic emission to occur at the direct band gap despite dominant intervalley electron scattering in these indirect gap NCs. Here, spin transitions can’t be resolved in the pico-second time scale using circularly polarized ultrafast optical excitation.
Relevant Publications
1. “Spin Polarization Dynamics of Free Charge Carriers in CsPbI 3 Nanocrystals”, S. Strohmair, A. Dey, Y. Tong, L. Polavarapu, B. J. Bohn, and J. Feldmann, submitted to Nano Letters
2. “Transfer of Direct to Indirect Bound Excitons by Electron Intervalley Scattering in Double Perovskite Nanocrystals”, A. Dey, A. F. Richter, T. Debnath, H. Huang, L. Polavarapu, and J. Feldmann, submitted to ACS Nano