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

摘要

In an effort to elucidate the spin (rather than charge) degrees of freedom incolloidal semiconductor nanocrystal quantum dots, we report on a series ofstatic and time-resolved photoluminescence measurements of colloidal CdSequantum 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 degreeof circular polarization with applied magnetic field, indicating the presenceof spin-polarized excitons. Time-resolved PL studies reveal a marked decreasein radiative exciton lifetime with increasing magnetic field and temperature.Except for an initial burst of unpolarized PL immediately followingphotoexcitation, high-field time-resolved PL measurements reveal a constantdegree of circular polarization throughout the entire exciton lifetime, even inthe presence of pronounced exciton transfer via Forster energy transferprocesses.