Picosecond energy transfer in quantum dot Langmuir-Blodgett nanoassemblies

TL;DR

This study investigates ultrafast energy transfer in quantum dot monolayers and bilayers assembled via Langmuir-Blodgett techniques, revealing picosecond transfer times and enhanced absorption due to inter-dot coupling.

Contribution

It provides a detailed spectrally resolved analysis of energy transfer dynamics and demonstrates engineered unidirectional transfer in bilayer quantum dot assemblies.

Findings

Energy transfer times range from 50 ps to 10 ns.

Enhanced absorption cross section up to 4 times for larger nanocrystals.

Fast, unidirectional energy flow of ~120 ps in bilayer structures.

Abstract

We study spectrally resolved dynamics of Forster energy transfer in single monolayers and bilayers of semiconductor nanocrystal quantum dots assembled using Langmuir-Blodgett (LB) techniques. For a single monolayer, we observe a distribution of transfer times from ~50 ps to ~10 ns, which can be quantitatively modeled assuming that the energy transfer is dominated by interactions of a donor nanocrystal with acceptor nanocrystals from the first three shells surrounding the donor. We also detect an effective enhancement of the absorption cross section (up to a factor of 4) for larger nanocrystals on the red side of the size distribution, which results from strong, inter-dot electrostatic coupling in the LB film (the light-harvesting antenna effect). By assembling bilayers of nanocrystals of two different sizes, we are able to improve the donor-acceptor spectral overlap for engineered transfer in a specific (vertical) direction. These bilayers show a fast, unidirectional energy flow with a time constant of ~120 ps.