Engineering Energy Harvesting Pathways in Mn‐Yb‐Doped Perovskite Nanocrystals

ABSTRACT Transition‐metal‐ and lanthanide‐doped perovskite nanocrystals (NCs) exhibit efficient dopant‐induced emission across the visible and near‐infrared spectrum. Here, we investigate Mn and Yb codoping in CsPbX 3 (X = Cl, Br) NCs as a means to control both the forward energy transfer (ET) and back energy transfer (BET) dynamics. While excitonic recombination in undoped NCs occurs on nanosecond timescales, doped NCs exhibit much longer, millisecond radiative lifetimes that enable controlled exciton management. Time‐gated band‐edge emission measurements further corroborate that BET pathways exist in these doped NCs. While singly doped NCs show BET from Mn‐dopant states or Yb‐vacancy‐induced defects, codoped NCs exhibit a synergistic mechanism. This effectively enhances the availability of carriers within the perovskite beyond their traditional excitonic lifetimes. As a result, an enhanced photocatalytic CO 2 reduction is observed for codoped NCs relative to undoped and singly doped analogues. Systematic bandgap engineering by anion exchange from chlorine to bromide‐rich perovskites, further enhances the energy harvesting capabilities, yielding an 8.6‐fold enhancement in the photocatalytic CO yield rate for Br‐rich Mn‐Yb codoped NCs compared to undoped Br‐rich mixed halide NC counterparts. These findings demonstrate that suitable bandgap engineering coupled with codoping in perovskite NCs offers a powerful strategy for engineering various light‐emission and harvesting pathways.