Hot electron and hole dynamics in thiol-capped CdSe quantum dots revealed by 2D electronic spectroscopy†
Nils Lenngren,Mohammed J. Al-Marri,Donatas Zigmantas,Tõnu Pullerits
Physical Chemistry Chemical Physics Pub Date : 08/25/2016 00:00:00 , DOI:10.1039/C6CP04190F
Abstract

Colloidal quantum dots (QDs) have attracted interest as materials for opto-electronic applications, wherein their efficient energy use requires the understanding of carrier relaxation. In QDs capped by bifunctional thiols, used to attach the QDs to a surface, the relaxation is complicated by carrier traps. Using 2D spectroscopy at 77 K, we follow excitations in thiol-capped CdSe QDs with state specificity and high time resolution. We unambiguously identify the lowest state as an optically allowed hole trap, and identify an electron trap with excited-state absorption. The presence of traps changes the initial dynamics entirely by offering a different relaxation channel. 2D electronic spectroscopy enables us to pinpoint correlations between states and to easily separate relaxation from different starting states. We observe the direct rapid trapping of 1S3/2, 2S3/2, and 1S1/2 holes, and several competing electron relaxation processes from the 1Pe state.

Graphical abstract: Hot electron and hole dynamics in thiol-capped CdSe quantum dots revealed by 2D electronic spectroscopy