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 Mn2+ by simple ligand assisted reprecipitation method. The reaction temperature and Pb to Mn feed ratio were optimized by preparing a series of Mn2+ - doped MAPbCl(3) NCs. The prepared NCs show bright Mn2+ emission with similar to 13% PL QY suggesting an efficient energy transfer from host NCs to Mn2+. 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 Mn2+ 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 Mn2+ PL emission in this host. These results reveal the origin of a temperature mediated energy transfer from exciton to Mn2+ and provide an understanding of the underlying mechanisms of PL properties of this new class of NCs.