Measurement of ligand coverage on cadmium selenide nanocrystals and its influence on dielectric dependent photoluminescence intermittency

Abstract

Photoluminescent quantum dots are used in a range of applications that exploit the unique size tuneable emission, light harvesting and quantum efficient properties of these semiconductor nanocrystals. However, optical instabilities such as photoluminescence intermittency, the stochastic switching between bright, emitting states and dark states, can hinder quantum dot performance. Correlations between this blinking of emission and the dielectric properties of the nanoenvironment between the quantum dot interface and host medium, suggest surface ligands play a role in modulating on-off switching rates. Here we elucidate the nature of the cadmium selenide nanocrystal surface, by combining magic angle spinning NMR and x-ray photoelectron spectroscopy to determine ligand surface densities, with molecular dynamics simulation to assess net ligand filling at the nanocrystal interface. Results support a high ligand coverage and are consistent with photoluminescence intermittency measurements that indicate a dominant contribution from surface ligand to the dielectric properties of the local quantum dot environment.

Near-Infrared-II Photodetectors Based on Silver Selenide Quantum Dots on Mesoporous TiO2 Scaffolds

“…The Ag 2 Se QDs lose ∼30% weight from 195 to 300 °C as determined by thermogravimetric analysis (TGA) (see Scheme S1b); i.e., the surface ligands occupy ∼30% weight, corresponding to a ligand density of 6.5/nm 2 (see detailed calculation in Scheme S1c). Fisher et al reported 2.3 ligand (stearic acid)/nm 2 on the surface of 3.0 nm in diameter CdSe QDs calculated from 1D proton NMR spectrum acquired by the magic angle spinning technique, and ∼29% coverage (ligand per atom) was estimated . Therefore, the seemingly high sulfur content in our Ag 2 Se QDS arises from the high DDT coverage on Ag 2 Se QD surface.…”

P band intermediate state (PBIS) tailors photoluminescence emission at confined nanoscale interface

“…Considering the diversity of the ligand binding motif and packing mode on the varied crystallographic planes of metal NCs 6,7,50-52 , the previously reported abnormal luminescence phenomena for metal NCs now can be readily understood due to the formation of diversity of PBIS at the nanoscale interface, such as solvent-induced dual-luminescence emissions, large Stokes shift (near-infrared emission), high quantum yield, long lifetime emission, broad emission peak, and ligand selectivity. We believe that this significant conceptual advance is not only useful for explaining the peculiar optoelectronic properties of semi-conductor quantum dots, carbon (or graphene) quantum dots and MOFs [1][2][3][4]49,[53][54][55][56] , but also provides completely new insights for the understanding of multiexcitonic relaxation of singlet fission and photoluminescent organometallic complexes 43,47,[57][58][59] .…”

Study of Physico-Chemical Changes of CdTe QDs after Their Exposure to Environmental Conditions

“…Until the last decade, most studies had focused on QDs of groups II-VI (most commonly CdSe or CdTe) [25][26][27]. Fisher et al described in detail the physical characteristics of CdSe QDs [28]. A typical diameter of QDs is in the range of 1 to 20 nm and may contain between 100 and 100,000 atoms per nanoparticle [29].…”