PbS/CdS Core–Shell Quantum Dots Suppress Charge Transfer and Enhance Triplet Transfer

Abstract

As ub-monolayer CdS shell on PbS quantum dots (QDs) enhances triplet energy transfer (TET) by suppressing competitive charge transfer from QDs to molecules.T he CdS shell increases the linear photon upconversion quantum yield (QY) from 3.5 %f or PbS QDs to 5.0 %f or PbS/CdS QDs when functionalizedw ith at etracene acceptor, 5-CT.W hile transient absorption spectroscopyr eveals that both PbS and PbS/CdS QDs show the formation of the 5-CT triplet (with rates of 5.91 AE 0.60 ns À1 and 1.03 AE 0.09 ns À1 respectively), ultrafast hole transfer occurs only from PbS QDs to 5-CT. Although the CdS shell decreases the TET rate,i te nhances TET efficiency from 60.3 AE 6.1 %to71.8 AE 6.2 %bysuppressing hole transfer.F urthermore,t he CdS shell prolongs the lifetime of the 5-CT triplet and thus enhances TET from 5-CT to the rubrene emitter,further bolstering the upconverison QY.

Anthracene Diphosphate Ligands for CdSe Quantum Dots; Molecular Design for Efficient Upconversion

“…Overall this supports a higher overall upconversion efficiency, [33][34][35] as the overall triplet energy transfer efficiency is increased by both the rate of TET and the transmitter triplet lifetime. The threshold intensity value is the point where the photon flux just replenishes the loss of the triplet excited states (due to various non-radiative loss processes + TTA processes which lead to upconversion).…”

Direct triplet sensitization of oligothiophene by quantum dots

“…In contrast to the absorption spectrum of T6 in toluene (Fig. 2 and S4†), the QD-bound T6 shows a red-shift of ∼20 nm, which is attributed to a change in the dielectric environment and has been observed in a similar system 30. The total amounts of T6 in the samples were obtained by subtracting QD only spectra from QD–T6 complex spectra.…”

Shallow distance-dependent triplet energy migration mediated by endothermic charge-transfer

“…Overall, both spin statistics and kinetic considerations should favor the formation of QD-3 ACA* over ground-state QD-ACA. We note that a few studies proposed a competition between hole transfer and TET from QDs to molecules [52][53][54] , or in another word, recombination of the hole-transfer CT state generates ground-state QD-molecule rather than molecular triplets. However, no direct spectroscopic evidence supporting this competition has been reported.…”