Mn(II)-doped 2D perovskite for light emitting devices.

Low dimensional perovskites are considered good candidates for light emitting applications given the high exciton binding energy which should in principle improve the radiative recombination efficiency. Yet, single-layered two-dimensional (2D) perovskite films are strongly limited by trap-assisted recombination and suffer from low luminescence yields, hampering their application in electroluminescence devices. Here, we use ad hoc synthetic and defect engineering strategies to overcome such issue. We employ metallic doping to controllably introduce luminescent impurities in a matrix made of 2D perovskite $NMA_{2}PbX_{4}$ based on the cation NMA = 1-naphtylmethylammonium. By means of temperature-dependent and time-resolved spectroscopy we demonstrate efficient energy transfer to $Mn^{2+}$ centres. Such process avoids the funnelling of the photo-excited species in inefficient recombination channels represented by intra-gap trap states and enhances photoluminescence, with quantum yield surpassing 20% in doped films. Eventually, we embody Mn-doped $NMA_{2}PbBr_{4}$ in a light emitting diode architecture and show, for the first time, electroluminescence from the $Mn^{2+}:^{4}T_{1}-^{6}A_{1}$ transition. This proof-of-concept demonstration shows the potential of doping in layered perovskites and prompt for the study of a wider range of host/guest structures.