Surface passivation extends single and biexciton lifetimes of InP quantum dots

Yang, Wenxing; Yang, Yawei; Kaledin, Alexey L.; He, Sheng; Jin, Tao; McBride, James R.; Lian, Tianquan

doi:10.1039/d0sc01039a

Cited by 61 publications

(116 citation statements)

References 62 publications

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“…15 Despite these studies, it has only been very recently that a TA study of InP nanocrystals has reported biexciton lifetimes for assynthesized and ZnS shell-passivated InP QDs. 16 The powerdependent bleach recovery kinetics indicate that surface passivation greatly increases the biexciton lifetimes. Passivation is provided by deposition of a very thin ZnS shell and is only partial; PL QYs of 35−40% are obtained.…”

Section: ■ Introductionmentioning

confidence: 99%

Auger Dynamics in InP/ZnSe/ZnS Quantum Dots Having Pure and Doped Shells

et al. 2021

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In this study, we report the negative trion and biexciton Auger dynamics in very high-quality InP/ZnSe/ZnS quantum dots (QDs) having varying amounts of indium-based traps in the ZnSe shell. Negative trion times are determined by time-correlated photon-counting measurements on QDs that have been photoreduced with lithium triethylborohydride. We find that the Auger times vary from 280 to 425 ps and scale linearly with the total particle volume. Excess indium in the ZnSe shell gives rise to hole traps that are transiently populated following photoexcitation. Comparing stoichiometric and nonstoichiometric particles, we find that the negative trion lifetimes are independent of the presence of indium in the ZnSe shell. Biexciton dynamics are determined from transient absorption (TA) bleach recovery measurements. Absorption of two photons results in the formation of two types of biexcitons: those having both holes in the InP core (XX state) and those having one hole trapped in the ZnSe shell (XT state). XX state Auger times are measured in stoichiometric QDs, and for these particles, the Auger times are ∼80 ps. Nonstoichiometric QDs show an additional long TA decay component, assigned to Auger recombination of the XT state. A previous study (J. Phys. Chem. C 2021, 125, 4110−4118) found that hole trapping at indium-based shell traps results in a slow photoluminescence (PL) rise component. We find that the fraction of the XT state formed by the absorption of two photon correlates with the product of the fraction of slow PL rise and the rise time constant following one-photon excitation.

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Section: ■ Introductionmentioning

confidence: 99%

Auger Dynamics in InP/ZnSe/ZnS Quantum Dots Having Pure and Doped Shells

et al. 2021

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“…Multiexcitonic states in colloidal quantum dots are usually studied by time-resolved photoluminescence and transient absorption spectroscopy. ,− These techniques enable one to measure, for example, the energies and dynamics of biexciton states. There are also some drawbacks, however.…”

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confidence: 99%

Observing Multiexciton Correlations in Colloidal Semiconductor Quantum Dots via Multiple-Quantum Two-Dimensional Fluorescence Spectroscopy

et al. 2021

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Correlations between excitons, that is, electron–hole pairs, have a great impact on the optoelectronic properties of semiconductor quantum dots and thus are relevant for applications such as lasers and photovoltaics. Upon multiphoton excitation, these correlations lead to the formation of multiexciton states. It is challenging to observe these states spectroscopically, especially higher multiexciton states, because of their short lifetimes and nonradiative decay. Moreover, solvent contributions in experiments with coherent signal detection may complicate the analysis. Here we employ multiple-quantum two-dimensional (2D) fluorescence spectroscopy on colloidal CdSe1–x S x /ZnS alloyed core/shell quantum dots. We selectively map the electronic structure of multiexcitons and their correlations by using two- and three-quantum 2D spectroscopy, conducted in a simultaneous measurement. Our experiments reveal the characteristics of biexcitons and triexcitons such as transition dipole moments, binding energies, and correlated transition energy fluctuations. We determine the binding energies of the first six biexciton states by simulating the two-quantum 2D spectrum. By analyzing the line shape of the three-quantum 2D spectrum, we find strong correlations between biexciton and triexciton states. Our method contributes to a more comprehensive understanding of multiexcitonic species in quantum dots and other semiconductor nanostructures.

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“…Considering the significant deviation from the power law dependence between the fast decay time (<10 ps) and the effective exciton radius (τ ∝ r n ) [ 39 ] in Figure S14, Supporting Information, we attribute the picosecond dynamics to the Auger‐assisted trapping dynamics. [ 40–43 ] The fast trapping terms in the decay profiles of a series of InP/ZnSe/ZnS QDs increased from 2.8 to 10 ps upon increasing the thickness of the ZnSe shell. While the trapping rates are inversely proportional to the ZnSe shell thickness, the energy difference Δ E between two bleaching bands (480–520 nm) in the DA spectra, assigned as band‐edge and trap states, becomes larger (Table 1).…”

Section: Resultsmentioning

confidence: 99%

Increasing the Energy Gap between Band‐Edge and Trap States Slows Down Picosecond Carrier Trapping in Highly Luminescent InP/ZnSe/ZnS Quantum Dots

Sung

Kim

Yun

et al. 2021

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Non‐toxic InP‐based nanocrystals have been developed for promising candidates for commercial optoelectronic applications and they still require further improvement on photophysical properties, compared to Cd‐based quantum dots (QDs), for better device efficiency and long‐term stability. It is, therefore, essential to understand the precise mechanism of carrier trapping even in the state‐of‐the‐art InP‐based QD with near‐unity luminescence. Here, it is shown that using time‐resolved spectroscopic measurements of systematically size‐controlled InP/ZnSe/ZnS core/shell/shell QDs with the quantum yield close to one, carrier trapping decreases with increasing the energy difference between band‐edge and trap states, indicating that the process follows the energy gap law, well known in molecular photochemistry for nonradiative internal conversion between two electronic states. Similar to the molecular view of the energy gap law, it is found that the energy gap between the band‐edge and trap states is closely associated with ZnSe phonons that assist carrier trapping into defects in highly luminescent InP/ZnSe/ZnS QDs. These findings represent a striking departure from the generally accepted view of carrier trapping mechanism in QDs in the Marcus normal region, providing a step forward understanding how excitons in nanocrystals interact with traps, and offering valuable guidance for making highly efficient and stable InP‐based QDs.

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Surface passivation extends single and biexciton lifetimes of InP quantum dots

Abstract: Combined optical spectroscopic study now reveals the photophysical changes of InP QDs upon surface passivation by various methods.

Cited by 61 publications

References 62 publications

Auger Dynamics in InP/ZnSe/ZnS Quantum Dots Having Pure and Doped Shells

Auger Dynamics in InP/ZnSe/ZnS Quantum Dots Having Pure and Doped Shells

Observing Multiexciton Correlations in Colloidal Semiconductor Quantum Dots via Multiple-Quantum Two-Dimensional Fluorescence Spectroscopy

Increasing the Energy Gap between Band‐Edge and Trap States Slows Down Picosecond Carrier Trapping in Highly Luminescent InP/ZnSe/ZnS Quantum Dots

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