Anomalous Laser-Fluence Dependence of Electron Spin Excitation in CdS Colloidal Quantum Dots: Surface Effects

Abstract

Electron spin dynamics in CdS quantum dots (QDs) with hole acceptor 1octanethiol organic molecules are investigated by time-resolved ellipticity spectroscopy. An anomalous dependence of laser fluences on electron spin excitation for the first time is reported. Increasing the laser fluence, the electron spin is switched from one direction to an antiparallel direction (spin direction switching, SDS) when adding enough 1-octanethiol hole acceptors in an air atmosphere. The analysis shows that the electron spin direction changes from heavy hole excitation defined to spin−orbit split hole excitation defined. In as-grown CdS QDs with native ligands, laser-fluence-dependent SDS phenomena are absent. Electron wave function spread into 1-octanethiol molecules is demonstrated to be important for the presence of SDS phenomena. The finding here thus reveals the importance of surface conditions on electron spin excitation processes in semiconductor QDs and that the surface can be used as an important factor to manipulate the spin.

Enhancement of Photoluminescence in CsPbBr3 Nanocrystals with 1-Octanethiol by Light Illumination for Potential Emitting Applications

“…On the other hand, the addition of some organic molecules, such as electron or hole acceptors, into CsPbX 3 NCs will weaken their PL intensities and lead to a charge separation state, − which is crucial for photocatalytic and photovoltaic applications. 1-Octanethiol (OT) is a well-known hole-acceptor in II–VI colloidal NCs, − which can sustain stable negative photocharging in CdSe quantum dots in both air and nitrogen (N 2 ) atmospheres . However, systematic investigations of carrier dynamics and PL performance in perovskite NCs with OT molecules are still lacking.…”

Coherent Spin Dynamics of Electrons in CdSe Colloidal Nanoplatelets

“…Spin studies of CdSe nanocrystals started more than 20 years ago [26][27][28] and still attract attention of researchers [29][30][31][32]. A very unusual effect has been found, i.e., the manifestation of surface spins, which strongly polarize exciton spins in CdSe NPLs at low temperatures [33].…”