Anomalous temperature dependence of the the spin-flip thermalization time between the dark and bright exciton states in silicon nanocrystals

TL;DR

This paper investigates the temperature-dependent thermalization time between dark and bright exciton states in silicon nanocrystals, revealing an unexpected increase in thermalization time at higher temperatures through time-resolved fluorescence spectroscopy.

Contribution

It reports the anomalous temperature dependence of exciton thermalization times in silicon nanocrystals, supported by a simple two-state model analysis.

Findings

Thermalization time is about 100 ns below 100 K.

Thermalization time increases unexpectedly at higher temperatures.

Decay curves fit a two-state exciton model.

Abstract

Silicon nanocrystals are studied by time-resolved fluorescence spectroscopy. After laser excitation the bright and dark exciton ground state levels are populated at random, but subsequently the decay curves reveal a thermalization between these levels. The characteristic thermalization time is found to be approximately 100 ns for temperatures below 100 K and surprisingly increases for higher temperatures. The decay curves are analyzed using a simple two-state model for the bright and dark exciton ground states.