Interplay of Conventional and Spin-Exchange Auger Recombination in Magnetically Doped Quantum Dots.

Abstract

Auger recombination strongly influences the photophysics of colloidal quantum dots (QDs), limiting light-emission efficiency while enabling the generation and manipulation of hot carriers via Auger up-conversion. Recent work has shown that incorporating magnetic manganese (Mn) dopants accelerates multiexciton Auger decay by two to three orders of magnitude─down to subpicosecond time scales─yet the underlying mechanism has remained unclear. Here, we demonstrate that ultrafast Auger recombination arises only from hybrid multiexciton states comprising intrinsic QD excitons coupled to Mn-based excitations. In this regime, the Auger rates exhibit no QD-size dependence and are governed solely by QD exciton occupancy, with no appreciable dependence on the number of excited Mn ions. These observations are inconsistent with a conventional Auger recombination scenario but can be rationalized by a spin-exchange (SE) mechanism involving two concerted spin-transfer events coupled through a virtual intermediate state. In this framework, the process effectively preselects a single excited Mn ion, while all others remain inactive. Unlike conventional Auger recombination, where the hot-carrier spin is not well-defined, the SE-mediated process generates carriers with well-defined spin polarization linked to the spin state of the participating Mn ion. These findings establish spin-exchange Auger recombination as an exceptionally fast energy-transfer pathway, outpacing both conventional Auger decay and phonon-assisted cooling. By enabling efficient generation and control of hot carriers, SE-mediated Auger recombination has important implications for photoconversion and photochemistry.