Horizontal versus vertical charge and energy transfer in hybrid assemblies of semiconductor nanoparticles

Abstract

SummaryWe studied the photoluminescence and time-resolved photoluminescence from self-assembled bilayers of donor and acceptor nanoparticles (NPs) adsorbed on a quartz substrate through organic linkers. Charge and energy transfer processes within the assemblies were investigated as a function of the length of the dithiolated linker (DT) between the donors and acceptors. We found an unusual linker-length-dependency in the emission of the donors. This dependency may be explained by charge and energy transfer processes in the vertical direction (from the donors to the acceptors) that depend strongly on charge transfer processes occurring in the horizontal plane (within the monolayer of the acceptor), namely, parallel to the substrate.

Near-Quantitative Yield for Transfer of Near-Infrared Excitons within Solution-Phase Assemblies of PbS Quantum Dots

“…The enhancement of the PL of the AQDs by energy transfer increases with increasing ratio of DQDs to AQDs even after correcting for the absolute number of photons absorbed (and appears to saturate at a factor of 3.0 at DQD:AQD = 1.5:1), but the quantum yield of energy transfer, defined as the percentage of excitons in the DQDs that transfer to an AQD, peaks at 90% at DQD:AQD = 1:1−1.5:1, probably due to a combination of optimal coupling yield and maximum mixing of DQDs and AQDs within assemblies. The time constants for energy transfer, 113 and 850 ns, are within the range of those measured for EnT between PbS QDs in the solid state, [19][20][21]23 and a factor of 2−10 slower than those measured for EnT between CdSe QDs in the solid state, 10,12,15,44 although the comparison is not entirely straightforward because the quoted rate constants are directly measured (and therefore could be convoluted with exciton hopping rate constants), while ours are "intrinsic", i.e., single-step, nearest-neighbor EnT determined from fitting our data with a multipathway kinetic model.…”

“…Here we report an exceptionally high yield of excitonic energy transfer (EnT) from smaller PbS QDs ( R = 1.6 nm) to larger PbS QDs ( R = 1.9 nm) within small assemblies of QDs dispersed in CHCl 3 . In the vast majority of studies on EnT among colloidal QDs, the QDs have been deposited as a film, and the interparticle distance minimized by ligand exchange from the “native” (as-synthesized) ligand to a shorter ligand. − For EnT of NIR excitons between PbS QDs, this strategy has resulted in reported time constants of 25–200 ns (and reported efficiencies between 35 and 99%). − There are however very few studies of EnT within solution-phase aggregates of QDs, − despite the potential applications of solution-phase FRET in biological and chemical sensing, , flow cytometry, and fundamental mechanistic analysis, in part because assembly of donor and acceptor QDs selective enough to realize high, or even measurable, EnT yield while maintaining solubility of the assembly is a challenge, especially in the NIR.…”

How Isolated Are the Electronic States of the Core in Core/Shell Nanoparticles?

“…This quenching is a result of a nonradiative decay pathway opened upon adsorption of the thiols and the formation of trap Since the TPPE signal is proportional to the timeaveraged population during the laser pulse, this dramatic increase in the intensity is a result of the excited electrons being transferred to longer-lived surface state traps, a process that lengthens their lifetime; as a result, the excited-state population increases, and so does the TPPE signal. This effect is supposed to decrease the PL lifetime of the excited NPs, as indeed was observed 27 consistent with the electron trap states formed on the surface of CdSe core-only NPs when changing their capping to a capping with thiolated molecules. 26 The unchanged intensities of the HOMO, upon adsorbing DT, can be explained by a relatively fast refilling time of electrons from the metal substrate back to the HOMO.…”

Electron Transfer in Nanoparticle Dyads Assembled on a Colloidal Template

“…In complex nanoscale systems, where electron transfer is studied as a function of distance, slopes that are much less than one are frequently reported. ,− Gilbert et al described molecular wires in which electrons can hop along the bridge, as well as tunnel through it, yielding smaller β values. In complex two-nanoparticle systems separated by “alkane-like” linkers, β values have been reported to be 0.08 and 0.13 per Å.…”