Spin flip from dark to bright states in InP quantum dots

TL;DR

This study measures the rapid spin flip time from dark to bright exciton states in InP quantum dots, revealing a faster process than in other systems, with implications for quantum dot luminescence dynamics.

Contribution

It provides the first measurement of spin flip times in InP quantum dots and shows these are significantly shorter than in other quantum dot materials.

Findings

Spin flip time is approximately 200 ps in InP quantum dots.

The luminescence decay time is about 300 ps, limited by dark-to-bright conversion.

Spin flip time is independent of density and temperature below 70 K.

Abstract

We report measurements of the time for spin flip from dark (non-light emitting) exciton states in quantum dots to bright (light emitting) exciton states in InP quantum dots. Dark excitons are created by two-photon excitation by an ultrafast laser. The time for spin flip between dark and bright states is found to be approximately 200 ps, independent of density and temperature below 70 K. This is much shorter than observed in other quantum dot systems. The rate of decay of the luminescence intensity, approximately 300 ps, is not simply equal to the radiative decay rate from the bright states, because the rate of decay is limited by the rate of conversion from dark excitons into bright excitons. The dependence of the luminescence decay time on the spin flip time is a general effect that applies to many experiments.