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

Abstract

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_<i>x</i>Cd_1-<i>x</i>S/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_<i>x</i>Cd_1-<i>x</i>S. This behavior is well correlated with ultrafast measurements which show orders-of-magnitude slower energy transfer from InP to Mn²⁺ dopants than Zn_<i>x</i>Cd_1-<i>x</i>S 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.