Low-Temperature Energy Transfer Self-Trapped Excitons in Mn-Doped 2D Organometal Halide Perovskites.

We investigate the mechanisms of energy transfer in Mn-doped ethylammonium lead bromide (EAPbBr:Mn), a two-dimensional layered perovskite (2DLP), using cryogenic optical spectroscopy. At temperature > 120 K, photoluminescence (PL) is dominated by emission from Mn, with complete suppression of band edge (BE) emission and self-trapped exciton (STE) emission. However, for < 120 K, in addition to Mn emission, PL is observed from BE and STEs. Data further reveal that for 20 K < < 120 K, STEs form the most dominant routes in assisting energy transfer (ET) from 2DLP to Mn dopants. However, at higher Mn concentration, higher activation energies indicate defect states come into play, successfully competing with STEs for ET both from BE to STE states and from STE to Mn. Finally, using polarization-resolved spectroscopy, we demonstrate optical spin orientation of the Mn ions via ET from 2DLP excitons at zero magnetic field. Our results reveal fundamental insights on the interactions between quantum confined charge carriers and dopants in organometal halide perovskites.