Low-Temperature Energy Transfer via Self-Trapped Excitons in Mn²⁺-Doped 2D Organometal Halide Perovskites

We investigate the mechanisms of energy transfer in Mn²⁺-doped ethylammonium lead bromide (EA₂PbBr₄:Mn²⁺), a two-dimensional layered perovskite (2DLP), using cryogenic optical spectroscopy. At temperature T > 120 K, photoluminescence (PL) is dominated by emission from Mn²⁺, with complete suppression of band edge (BE) emission and self-trapped exciton (STE) emission. However, for T < 120 K, in addition to Mn²⁺ emission, PL is observed from BE and STEs. Data further reveal that for 20 K < T < 120 K, STEs form the most dominant routes in assisting energy transfer (ET) from 2DLP to Mn²⁺ dopants. However, at higher Mn²⁺ 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 Mn²⁺. Finally, using polarization-resolved spectroscopy, we demonstrate optical spin orientation of the Mn²⁺ 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.