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

Abstract

Auger processes play a critical role in the behavior of colloidal quantum dots (QDs). While nonradiative Auger recombination is a key performance-limiting factor in light-emitting applications, Auger effects also present exciting opportunities for hot-carrier manipulation in emerging optoelectronic and photochemical technologies. Recent studies have shown that incorporating magnetic manganese (Mn) dopants into QDs enables an ultrafast spin-exchange (SE) mechanism that significantly accelerates Auger recombination and related processes. However, the fundamental dynamics of SE-Auger recombination, including its dependence on QD size, exciton multiplicity, and Mn-ion content, remain largely unexplored. Here, we investigate SE-Auger recombination in Mn-doped QDs across three regimes defined by the energetic alignment between the QD band-edge exciton and the internal Mn spin-flip transition: resonant, downhill, and uphill, corresponding to the exciton energy being approximately equal to, greater than, or smaller than the Mn spin-flip transition energy, respectively. We find that SE-Auger recombination dominates multiexciton dynamics in both resonant and downhill regimes, proceeding on ultrafast, sub-picosecond timescales, that is, significantly faster than conventional Auger decay. Notably, SE-Auger lifetimes are primarily governed by the occupancy of intrinsic excitonic states, with minimal dependence on QD size or the number of excited Mn ions. In the uphill regime, SE-Auger recombination coexists with conventional Auger processes, enabling direct comparison of their timescales alongside co-occurring hot-carrier cooling. These findings establish that SE-Auger recombination outpaces phonon-assisted cooling, making it uniquely suited for the generation and manipulation of hot carriers, and opening new avenues in advanced photoconversion and photochemistry.