Surface spin magnetism controls the polarized exciton emission from CdSe nanoplatelets

TL;DR

This study demonstrates that surface spin magnetism in CdSe nanoplatelets influences their polarized exciton emission, with magnetic field-dependent effects revealing the role of dangling bond spins and their exchange interactions.

Contribution

It uncovers how surface paramagnetism from dangling bonds affects exciton polarization and emission in CdSe nanoplatelets, linking growth conditions to magnetic interactions.

Findings

Circular polarization depends nonlinearly on magnetic field up to 15 Tesla.

Surface dangling bonds induce paramagnetism affecting exciton spin polarization.

Exchange interaction sign can be tuned by nanoplatelet growth conditions.

Abstract

The surface of nominally diamagnetic colloidal CdSe nanoplatelets can demonstrate paramagnetism owing to the uncompensated spins of dangling bonds (DBSs). We reveal that by optical spectroscopy in high magnetic fields up to 15 Tesla using the exciton spin as probe of the surface magnetism. The strongly nonlinear magnetic field dependence of the circular polarization of the exciton emission is determined by the DBS and exciton spin polarization as well as by the spin-dependent recombination of dark excitons. The sign of the exciton-DBS exchange interaction can be adjusted by the nanoplatelet growth conditions.