Auger recombination plays a pivotal role in the photophysics of colloidal quantum dots (QDs), limiting light-emission efficiency while also providing a pathway to generate and manipulate hot, unrelaxed carriers. When the Auger process is  sufficiently fast, it can enable efficient electron photoemission—a phenomenon attracting considerable interest for its potential application in technologies ranging from photomultipliers and night-vision devices to redox photochemistry, high-resolution electron microscopy, and free-electron lasers.

Since the electron affinity (E_a) in QDs is usually larger than the bandgap energy (E_g), promotion of an electron above the QD vacuum level requires at least two consecutive Auger steps, with the second step involving re-excitation of the hot carrier generated by the first Auger-recombination event. In conventional (undoped) QDs, however, this multi-step Auger photoemission process is strongly suppressed by competing energy losses through phonon emission, which causes rapid electron cooling before the second Auger  step can occur.

In 2019, we reported that ultrafast spin-exchange (SE) interactions in Mn-doped colloidal CdSe QDs lead to a dramatic enhancement of the Auger recombination rate, making it faster carrier cooling via phonons¹. This discovery enabled us to demonstrate highly efficient visible-light driven generation of solvated electrons using Mn-doped CdSe QDs dispersed in water², achieving quantum efficiency of up to ~3%.

While demonstrating its considerable potential for generating and manipulating hot carriers, SE Auger recombination remains poorly understood from a mechanistic standpoint. To address this gap, we recently carried out a detailed investigation of SE Auger recombination in a series of Mn-doped QDs with bandgaps tuned from below to above the energy of the Mn spin-flip transition³.

From these studies, we conclude that observation of ultrafast Auger recombination requires the formation of a hybrid multiexciton state composed of intrinsic QD excitons and Mn-based excitations. In this regime, Auger recombination proceeds via a cross-relaxation process mediated by strong Coulomb-exchange interactions involving two correlated spin transfers between the QD and an excited Mn ion. We find that the Auger rate depends solely on QD exciton occupancy, rather than on the number of excited Mn ions, and exhibits no size dependence —features unusual for conventional Auger recombination but fully consistent with an SE-driven process.

These findings resolve the long-standing puzzle of Mn-induced Auger decay acceleration and provide design principles for tailoring QD properties through energetic alignment and controlled magnetic doping.