Temperature-dependent anomalous Mn2+ emission and excited state dynamics in Mn2+-doped MAPbCl3-xBrx nanocrystals

In hybrid perovskites, MAPbI 3 and MAPbBr 3 have been extensively studied for their optical and photovoltaic properties, but MAPbCl 3 is significantly less investigated for its optical and photovoltaic properties due to its low photoluminescence quantum yield (PL QY) and a large band gap. However, the large band gap makes it a suitable host for doping transition metal ions to explore new optical properties. We synthesized nanocrystals (NCs) of MAPbCl 3 doped with Mn 2+ by simple ligand assisted reprecipitation method. The reaction temperature and Pb to Mn feed ratio were optimized by preparing a series of Mn 2+ -doped MAPbCl 3 NCs. The prepared NCs show bright Mn 2+ emission with ~13% PL QY suggesting an efficient energy transfer from host NCs to Mn 2+ . Since the large bandgap of MAPbCl 3 precludes the possibility of investigating temperature-dependent PL and lifetime measurements to understand the excited state dynamics, we carried out these experiments on Mn 2+ doped MAPbCl 2.7 Br 0.3 with the Br concentration adjusted to bring the bandgap of the alloyed system within the limits of the experimental technique. Our studies establish an anomalous behavior of Mn 2+ PL emission in this host. These results reveal the origin of a temperature mediated energy transfer from exciton to Mn 2+ and provide an understanding of the underlying mechanisms of PL properties of this new class of NCs. Graphical abstract SYNOPSIS: Nanocrystals (NCs) of MAPbCl 3-x Br x doped with Mn 2+ were prepared by simple ligand assisted reprecipitation method. Reaction temperature and Mn 2+ concentrations were optimized to achieve maximum Mn 2+ emission. The temperature-dependent photoluminescence results reveal the origin of temperature mediated energy transfer from exciton to Mn 2+ in MAPbCl 3-x Br x NCs.