Single Trap States in Single CdSe Nanoplatelets

Hinterding, Stijn; Salzmann, Bastiaan B. V.; Vonk, Sander J. W.; Vanmaekelbergh, Daniël; Weckhuysen, Bert M.; Hutter, Eline M.; Rabouw, Freddy T.

doi:10.1021/acsnano.1c00481

Cited by 41 publications

(45 citation statements)

References 59 publications

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“…While it is often assumed that τ X – ,r is half the radiative lifetime of neutral excitons (τ X,r ), the latter has never been accurately measured or derived. As shown in Figure S12, the PL decay of neutral NPLs is multiexponential, with contributions from carrier trapping, exciton radiative recombination, carrier detrapping, and recombination of detrapped carriers, , rendering the extraction of pure exciton radiative recombination almost impossible. For this reason, we cannot quantify τ X – ,r and τ X – ,A for our 4 ML and core/shell NPLs.…”

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confidence: 99%

Colloidal n-Doped CdSe and CdSe/ZnS Nanoplatelets

Wang

Xiang

Gao

et al. 2021

J. Phys. Chem. Lett.

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Colloidal semiconductor nanoplatelets (NPLs) are chemical versions of well-studied quantum wells (QWs). For QWs, gating and carrier doping are standard tools to manipulate their optical, electric, or magnetic properties. It would be highly desirable to use pure chemical methods to dope extra charge carriers into free-standing colloidal NPLs to achieve a similar level of manipulation. Here we report colloidal n-doped CdSe and CdSe/ZnS NPLs achieved through a photochemical doping method. The extra electrons doped into the conduction band edges are evidenced by exciton absorption bleaches recoverable through dedoping and the appearance of new intersub-band transitions in the near-infrared. A high surface ligand coverage is the key to successful doping; otherwise, the doped electrons can be depleted likely by unpassivated surface cations. Large trion binding energies of 20–30 meV are found for the n-doped CdSe NPLs, which, in contrast, are reduced by 1 order of magnitude in CdSe/ZnS core/shell NPLs due to dielectric screening. Furthermore, we identify a long-lived negative trion with a lifetime of 1.5–1.6 ns that is likely dominated by radiative recombination.

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confidence: 99%

Colloidal n-Doped CdSe and CdSe/ZnS Nanoplatelets

Wang

Xiang

Gao

et al. 2021

J. Phys. Chem. Lett.

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“…The low-energy band exhibits a broad and weak appearance and is nearly vanished at elevated temperatures. The trapping centers are presumably related to surface sites that can capture hole carriers at metal vacancy sites produced by Se-rich surfaces . This broad emission band retains a constant energy shift by ∼0.57 eV from the exciton region, proposing a relation to deep states.…”

Section: Results and Discussionmentioning

confidence: 93%

“…The trapping centers are presumably related to surface sites that can capture hole carriers at metal vacancy sites produced by Se-rich surfaces. 34 This broad emission band retains a constant energy shift by ∼0.57 eV from the exciton region, proposing a relation to deep states. Further discussion about the lowest energy band is beyond the scope of this paper.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Room Temperature Colloidal Coating of II–VI Nanoplatelets with Quantum Dots

2021

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The low-temperature colloidal production of II−VI nanoplatelet heterostructures has stimulated the interest of researchers due to the possible uses of these materials in various optoelectronic devices. Here, we report a roomtemperature coating by CdS or ZnS dots of preprepared CdSe nanoplatelets. The dot coating process made use of a synthesis developed for the formation of freestanding CdS and ZnS species, involving injection of a metal precursor into reactive sulfur−amine solutions at room temperature. CdSe structured nanoplatelets with 1.75 nm thickness were used as the core constituent. The structural properties were investigated using Fourier transform infrared spectroscopy and advanced electron microscopy, while the elemental mapping was verified using high-angle annular dark field transmission electron microscopy. The results showed a dots-on-plate structure, resembling an intermediate configuration between core/crown or core/shell heterostructures. A thorough study of optical properties demonstrated a dramatic spectral shift of the absorption edge to lower energies, regardless of the uniformity of the coating layer, maintaining spectral stability over two months while stored at ambient conditions. Other optical measurements included examination of temperature-dependent photoluminescence and transient photoluminescence decay, from room temperature down to ∼4 K. These measurements revealed excitons, trions, and trapped carrier recombination emission with variable relative intensities following the temperature change. The dots-on-plate structures studied displayed a short photoluminescence decay (≤nanosecond), compatible with that of core/shell (crown) structures prepared at high temperatures. As a result, the presented techniques are alternative pathways that eliminate the requirement for excessive temperatures and/or multistep processes, instead providing rapid, inexpensive, and scalable procedures with practical advantages.

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“…The correlation of slower blinking dynamics with SD indicates that blinking on this time scale (≥3 s) is due to switching between different emissive states, particularly excitons and trions (mechanism 2, Figure 1). This result is consistent with previous work that concluded that switching between excitons and trions occurs slower than 100 ms. 51 Given that the trion states persist for seconds, the surfacetrapped carriers that have escaped from the NPL to form the trion must require unlikely detrapping events to return to a neutral exciton or biexciton before returning to the ground state. This conclusion is consistent with the observation that low-temperature emission spectra of NPLs are dominated by trion emission.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Evidence for Two Time Scale-Specific Blinking Mechanisms in Room-Temperature Single Nanoplatelets

Irgen-Gioro

López-Arteaga

et al. 2021

J. Phys. Chem. C

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Intermittent periods of low light emission (“blinking”) and time-dependent emission spectra (spectral diffusion, SD) have proven to be major obstacles to the adoption of colloidal semiconductor nanocrystals as quantum emitters. One clue to the mechanisms behind these two phenomena is how they are related, which is difficult to determine at time scales faster than can be captured using a spectrometer (∼100 ms). This work utilizes spectral correlations to access a range of time scales from 10 μs to 10 s and determines that, for quasi-2D CdSe/CdS core/shell nanoplatelets (NPLs), blinking occurs on time scales from 100 μs to seconds but is only accompanied by SD on the ∼1 s time scale and slower. This result indicates that shorter time scale blinking is due only to an equilibrium between dark and bright states with a shared, uncharged ground state, while longer time scale blinking receives contributions from an equilibrium between two distinct emissive states. The 10–15 meV energy range sampled by the NPL emission during SD implies that the two emissive states are an exciton and a trion.

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Single Trap States in Single CdSe Nanoplatelets

Cited by 41 publications

References 59 publications

Colloidal n-Doped CdSe and CdSe/ZnS Nanoplatelets

Colloidal n-Doped CdSe and CdSe/ZnS Nanoplatelets

Room Temperature Colloidal Coating of II–VI Nanoplatelets with Quantum Dots

Evidence for Two Time Scale-Specific Blinking Mechanisms in Room-Temperature Single Nanoplatelets

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