Time- and Polarization-Resolved Optical Spectroscopy of Colloidal CdSe Nanocrystal Quantum Dots in High Magnetic Fields

TL;DR

This study investigates the spin properties of colloidal CdSe nanocrystal quantum dots using high magnetic field optical spectroscopy, revealing spin polarization and exciton dynamics at low temperatures.

Contribution

It provides new insights into spin-polarized excitons and their dynamics in colloidal quantum dots under ultra-high magnetic fields, a novel experimental approach.

Findings

High degree of circular polarization in PL at high magnetic fields

Decrease in exciton lifetime with increasing magnetic field and temperature

Constant circular polarization during exciton lifetime despite energy transfer processes

Abstract

In an effort to elucidate the spin (rather than charge) degrees of freedom in colloidal semiconductor nanocrystal quantum dots, we report on a series of static and time-resolved photoluminescence measurements of colloidal CdSe quantum dots in ultra-high magnetic fields up to 45 Tesla. At low temperatures (1.5 K - 40 K), the steady-state photoluminescence (PL) develops a high degree of circular polarization with applied magnetic field, indicating the presence of spin-polarized excitons. Time-resolved PL studies reveal a marked decrease in radiative exciton lifetime with increasing magnetic field and temperature. Except for an initial burst of unpolarized PL immediately following photoexcitation, high-field time-resolved PL measurements reveal a constant degree of circular polarization throughout the entire exciton lifetime, even in the presence of pronounced exciton transfer via Forster energy transfer processes.