Spin-Exchange Interaction in Mn²⁺-Doped InP Colloidal Quantum Dots Revealed through Correlated Magneto-Optical Spectroscopy and Transient Carrier Dynamics

Previous studies on Mn²⁺-doped colloidal quantum dots (QDs) mostly focused on Cd-based QDs, whereas Mn²⁺-doped III–V group InP QDs, which not only represent an environmentally friendly alternative but also could enable potential opportunities for ferromagnetism, have remained relatively underexplored. Here we systematically investigated the magneto-optical spectroscopy and carrier dynamics in Mn²⁺-doped InP/ZnS core/shell QDs and made a comprehensive, side-to-side comparison to doped Zn_xCd_1–xS/ZnS QDs of similar optical gap. Our cryogenic magnetic circular dichroism spectroscopy reveals much weaker (and inverted-sign) exchange interaction between InP and Mn²⁺ dopants in comparison to Zn_xCd_1–xS. This behavior is well correlated with ultrafast measurements which show orders-of-magnitude slower energy transfer from InP to Mn²⁺ dopants than Zn_xCd_1–xS and the absence of a rapid spin-exchange Auger recombination in the former. These findings provide crucial fundamental insights into spin-exchange mechanisms in Mn²⁺-doped colloidal QDs, with also important implications for the optimization and enhancement of the host–dopant interaction in Mn²⁺-doped InP QDs.