Highly efficient carrier multiplication in inverted CdSe/HgSe quantum dots mediated by magnetic impurities

Abstract

Incorporating manganese (Mn) impurities into II-VI semiconductors alters their properties through strong exchange interactions with the host material. In colloidal quantum dots (QDs), these interactions enable ultrafast bidirectional energy transfer between the magnetic impurity and the QD intrinsic states, with rates exceeding the rate of energy loss via phonon emission. This suggests that Mn-QD interactions could harness hot carrier energy before dissipation. Here, we demonstrate that by using Mn-doped CdSe/HgSe core/shell QDs, we can efficiently convert the kinetic energy of a hot exciton into an additional electron-hole pair. This spin-exchange carrier multiplication occurs through the rapid capture of a hot exciton by a Mn ion, which then undergoes spin-flip relaxation, producing two excitons near the QD band edge. Due to the inverted band structure of CdSe/HgSe QDs, where the shell has a lower bandgap than the core, both electrons and holes produced via carrier multiplication localize in the shell. This facilitates their efficient extraction, making these QDs promising for applications in electro-optical devices and photochemical reactions.