Temperature Dependent Anomalous Mn2+ Emission and Excited State Dynamics in Mn2+-Doped MAPbCl3-xBrx Nanocrystals

In hybrid perovskites, MAPbI₃ and MAPbBr₃ have been extensively studied for their optical and photovoltaic properties, but MAPbCl₃ 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 MAPbCl₃ 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 MAPbCl₃ NCs. The prepared NCs show bright Mn²⁺ emission with ~13% PL QY suggesting an efficient energy transfer from host NCs to Mn²⁺. Since the large bandgap of MAPbCl3 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_2.7Br_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 provides an understanding of the underlying mechanisms of PL properties of this new class of NCs.