Bimolecular Auger Recombination of Electron–Hole Pairs in Two-Dimensional CdSe and CdSe/CdZnS Core/Shell Nanoplatelets

Abstract

We have determined the Auger recombination kinetics of electrons and holes in colloidal CdSe-only and CdSe/CdS/ZnS core/shell nanoplatelets by time-resolved photoluminescence measurements. Excitation densities as high as an average of 18 electron−hole pairs per nanoplatelet were reached. Auger recombination can be described by second-order kinetics. From this we infer that the majority of electrons and holes are bound in the form of neutral excitons, while the fraction of free charges is much smaller. The biexciton Auger recombination rate in nanoplatelets is more than 1 order of magnitude smaller than for quantum dots and nanorods of equal volume. The latter is of advantage for application in lasers, light-emitting diodes, and photovoltaics.

Picosecond energy transfer and multiexciton transfer outpaces Auger recombination in binary CdSe nanoplatelet solids

“…Emitted photons were collected with a lens and directed to a 150 mm spectrograph and single-photon-sensitive streak camera. Except where noted, fluence was adjusted to an intensity corresponding to less than 1 exciton per NPL on average 15,31 , and this was further verified by ensuring that data collected at three times higher and lower fluence showed fluence independence. Fluence-dependent data were collected using a 312-µm-diameter pump spot.…”

Two‐Dimensional Visible Spectroscopy For Studying Colloidal Semiconductor Nanocrystals

“…[ 21 ] Exciton-exciton and carrier-carrier interactions lead to specifi c power-dependent behavior and are used to identify the nature of the species generated after photoexcitation as well as their fate. [ 22 ] Temperature-dependent TR-PL measurements have revealed information about the fi ne structure of the lowest energy exciton in CdSe nanocrystals (also known as colloidal quantum dots, Qds) with noticeable biexponential behavior at low temperature due to the presence of a low-emitting exciton state (called a "dark state") just below the lowest bright exciton state. [ 23,24 ] The sensitivity of fl uorescence detection has enabled the fl uorescence lifetime of single nanocrystals to be recorded, leading to intrinsic decay rates sometimes being concealed in ensemble measurements.…”

Platelet‐in‐Box Colloidal Quantum Wells: CdSe/CdS@CdS Core/Crown@Shell Heteronanoplatelets

“…[ 22 ] Also, a higher level of photoluminescence quantum yield (up to 80%) is achieved for CdSe@CdS C@S NPLs synthesized with one-pot synthesis. [ 22 ] In addition, CdSe@CdS C@S NPLs, due to the separation of electron and hole wave functions, exhibit suppressed Auger recombination (AR) [ 23 ] with reduced blinking behavior [ 22 ] . With their promising properties, light-emitting diodes having narrower emission bandwidths [ 24 ] and optically pumped lasers with very low threshold [ 25 ] have been demonstrated by using NPLs in the C@S architecture.…”