Manipulation and Mechanistic Understanding of Exciton Spin Dynamics in a Chiral Inorganic Nanosystem via Facile pH-Regulation

Abstract

This study demonstrates effective manipulation of exciton spin dynamics in a prototypical chiral inorganic nanosystem, i.e., cadmium selenide (CdSe) nanosheets capped with chiral cysteine ligands in aqueous solution, via facile pH-regulation that can directly modify the electronic coupling between CdSe and cysteine's thiol group through Cd─S bonding. The comparative scrutiny by using transient circular dichroism spectroscopy enables to decipher the pertinent mechanisms behind the pH-regulated spin-flip dynamics. The hole-trapping interaction between the valence-band heavy-hole spin state of CdSe and the cysteine-induced “extrinsic” surface state is found to play a dominant role in prolonging the hole spin relaxation lifetime (by more than threefold). This study also demonstrates a relevant application in modulating the sensitivity of circularly polarized light detection. This work sets a paradigm for harnessing the elusive interactions in chiral inorganic nanosystems to achieve desired spin-polarization regulation, refreshing the fundamental understanding about the mechanisms of spin dynamics involved therein.