Multiexcitons confined within a sub-excitonic volume: Spectroscopic and dynamical signatures of neutral and charged biexcitons in ultrasmall semiconductor nanocrystals

TL;DR

This study uses ultrafast spectroscopy to investigate neutral and charged biexcitons in ultrasmall CdSe nanocrystals, revealing their high interaction energies and ultrafast nonradiative decay processes.

Contribution

It provides detailed spectroscopic and dynamical signatures of biexcitons in sub-10 nm nanocrystals, highlighting their giant interaction energies and rapid relaxation dynamics.

Findings

Giant interaction energies of tens to hundreds of meV for biexcitons.

Ultrafast lifetimes from sub-100 ps to sub-1 ps.

Efficient nonradiative Auger recombination causes rapid decay.

Abstract

The use of ultrafast gating techniques allows us to resolve both spectrally and temporally the emission from short-lived neutral and negatively charged biexcitons in ultrasmall (sub-10 nm) CdSe nanocrystals (nanocrystal quantum dots). Because of forced overlap of electronic wave functions and reduced dielectric screening, these states are characterized by giant interaction energies of tens (neutral biexcitons) to hundreds (charged biexcitons) of meV. Both types of biexcitons show extremely short lifetimes (from sub-100 picoseconds to sub-picosecond time scales) that rapidly shorten with decreasing nanocrystal size. These ultrafast relaxation dynamics are explained in terms of highly efficient nonradiative Auger recombination.