The Role of Ligands in Determining the Exciton Relaxation Dynamics in Semiconductor Quantum Dots

Abstract

This article reviews the mechanisms through which molecules adsorbed to the surfaces of semiconductor nanocrystals, quantum dots (QDs), influence the pathways for and dynamics of intra- and interband exciton relaxation in these nanostructures. In many cases, the surface chemistry of the QDs determines the competition between Auger relaxation and electronic-to-vibrational energy transfer in the intraband cooling of hot carriers, and between electron or hole-trapping processes and radiative recombination in relaxation of band-edge excitons. The latter competition determines the photoluminescence quantum yield of the nanocrystals, which is predictable through a set of mostly phenomenological models that link the surface coverage of ligands with specific chemical properties to the rate constants for nonradiative exciton decay.

Two‐Dimensional Visible Spectroscopy For Studying Colloidal Semiconductor Nanocrystals

“…[ 100 ] In addition, it was also shown that ultrafast electron relaxation can take place through Auger cooling, where the excess energy is transferred to the hole. [ 101 ] State-to-state relaxation can be measured in 2DES with the growth of cross peaks at high excitation and low detection energies corresponding to the optical transitions of interest.…”

Investigating the Control by Quantum Confinement and Surface Ligand Coating of Photocatalytic Efficiency in Chalcopyrite Copper Indium Diselenide Nanocrystals

“…[1][2][3][4][5][6] Given the NC composition, there are two important structural parameters -size ("quantum confinement effect") and the surface ligand chemistry of NCs -that control light absorption, enhance photogenerated charge separation, and reduce charge recombination, which together determine the catalytic efficiency. [7][8][9][10][11][12][13][14] Anatase TiO 2 is considered to be the most efficient and environmentally friendly photocatalyst. 15 However, its large band gap (~3.4 eV) allows only ultraviolet light absorption, which hinders its potential photocatalytic applications and commercialization.…”

Fluorescent carbon nanodots for optical detection of fluoride ion in aqueous media

“…In fact, thiolates have been classified as electron donor ligands with hole trapping properties [28]. A study on carrier dynamics of QDs has shown that surface bound thiolates can affect the optical properties of QDs by trapping photogenerated holes on the surface of QDs.…”