Fine Structure of Nearly Isotropic Bright Excitons in InP/ZnSe Colloidal Quantum Dots

Brodu, Annalisa; Chandrasekaran, Vigneshwaran; Scarpelli, Lorenzo; Buhot, Jonathan; Masia, Francesco; Ballottin, Mariana V.; Severijnen, Marion E.; Tessier, Martine; Dupont, Dorian; Rabouw, Freddy T.; Christianen, Peter C. M.; Donegá, Celso de Mello; Vanmaekelbergh, Daniël; Langbein, Wolfgang Werner; Hens, Zeger

doi:10.1021/acs.jpclett.9b01824

Cited by 25 publications

(40 citation statements)

References 28 publications

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“…More precisely, we used a laser with a linewidth of ∼300-μeV FWHM, which is narrow compared to the inhomogeneously broadened QD spectrum (150-meV FWHM; see Fig. S1) or even the homogeneously broadened single-QD spectrum measured in our previous work (3-meV FWHM [32]). By exciting on the low-energy side of the absorption spectrum, only the QDs with a high oscillator strength exciton state (bright state) that matches the energy of the excitation photons are excited.…”

Section: B Raman and Fluorescence Line Narrowing Spectroscopymentioning

confidence: 99%

Exciton-phonon coupling in InP quantum dots with ZnS and (Zn,Cd)Se shells

et al. 2020

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InP-based colloidal quantum dots are promising for optoelectronic devices such as light-emitting diodes and lasers. Understanding and optimizing their emission process is of scientific interest and essential for large-scale applications. Here we present a study of the exciton recombination dynamics in InP QDs with various shells: ZnS, ZnSe, and (Zn,Cd)Se with different amounts of Cd (5, 9, 12%). Phonon energies extracted from Raman spectroscopy measurements at cryogenic temperatures (4-5 K) are compared with exciton emission peaks observed in fluorescence line narrowing spectra. This allowed us to determine the position of both the bright F = ±1 state and the lowest dark F = ±2 state. We could identify the phonon modes involved in the radiative recombination of the dark state and found that acoustic and optical phonons of both the core and the shell are involved in this process. The Cd content in the shell increases electron wave-function delocalization, and thereby enhances the exciton-phonon coupling through the Fröhlich interaction.

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Section: B Raman and Fluorescence Line Narrowing Spectroscopymentioning

confidence: 99%

Exciton-phonon coupling in InP quantum dots with ZnS and (Zn,Cd)Se shells

et al. 2020

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“…We further note that the g factors we observed for PbS/CdS QDs are comparable in magnitude to those reported for CdSe, [ 34 ] CdSe/ZnS, [ 3 ] and InP/ZnSe QDs. [ 33 ] Increase of the g factor with transition energy has also been observed for CdSe [ 34 ] and InP/ZnS QDs. [ 35 ]…”

Section: Resultsmentioning

confidence: 93%

“…The Δ E xy values of 104–325 μeV are significantly smaller than the reported 0.5–3 meV splitting in CdSe QDs [ 32 ] and nearly quasi‐isotropic excitons recently reported in InP/ZnSe QDs. [ 33 ] These smaller Δ E xy values, together with an inability to observe any splitting in ensemble measurements, indicate that our PbS QDs maintain relatively good cubic symmetry. Furthermore, we note that these fine structure splittings also fall in the same order of magnitude as the 300–900 μeV splitting between the two lowest‐energy emitting states reported to have comparable lifetimes in the temperature‐dependent time‐resolved PL experiment on PbSe QDs.…”

Section: Resultsmentioning

confidence: 95%

Interplay of Bright Triplet and Dark Excitons Revealed by Magneto‐Photoluminescence of Individual PbS/CdS Quantum Dots

Kim

Avdeev

et al. 2021

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A low‐temperature polarization‐resolved magneto‐photoluminescence experiment is performed on individual PbS/CdS core/shell quantum dots (QDs). The experiment enables a direct measurement of the exciton Landé g factor and the anisotropic zero‐field splitting of the lowest emissive bright exciton triplet in PbS/CdS QDs. While anisotropic splittings of individual QDs distribute randomly in 104—325 μeV range, the exciton Landé g factors increase from 0.95 to 2.70 as the emission energy of the QD increases from 1.0 to 1.2 eV. The tight‐binding calculations allow to rationalize these trends as a direct consequence of reducing a cubic symmetry of QD via addition/removal of a few (<70) atoms from the surfaces of the PbS core. Furthermore, it is observed that while right (σ +) and left (σ −) circularly polarized photoluminescence (PL) peaks split linearly with magnetic field as expected for Zeeman effect, the energy splitting between X and Y linearly polarized PL peaks remains nearly unchanged. The theoretical study reveals rich and complex magnetic field‐induced interplay of bright triplet and dark exciton states explaining this puzzling behavior. These findings fill the missing gaps in the understanding of lead salt QDs and provide foundation for development of classical and quantum light sources operating at telecommunication wavelengths.

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“…Note that this finding is in line with published emission spectra of single InP/ZnSe QDs, where the biexciton emission was observed a mere 9.5 meV to the red of the exciton line. 29 Interestingly, as compared to the biexciton shift, the band-edge photoluminescence exhibits a…”

Section: Stimulated Emission -Model Descriptionmentioning

confidence: 99%

“…Ensemble-level and single-dot photoluminescence studies showed fine-structure properties and radiative lifetimes characteristic of strongly confined excitons. 25,28,29 Nevertheless, the presence of substitutional zinc that acts as a shallow hole trap was linked to the relatively broad, presumably trap-related, emission line of InP-based QDs. 30 While synthesisdependent variations of zinc incorporation may account for these differences, 31 this unclarity mostly calls for more insight in the opto-electronic properties of photo-excited InP-based QDs.…”

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State Filling and Stimulated Emission by Colloidal InP/ZnSe Core/Shell Quantum Dots

Velosa

Avermaet

Schiettecatte

et al. 2022

Preprint

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Colloidal InP-based quantum dots (QDs) have been widely studied for luminescent color conversion or electroluminescence, yet the nature of the emitting state remains a matter of debate and reports on stimulated emission by these materials are nearly absent. Here, we investigate the properties of photo-excited InP/ZnSe QDs using femtosecond transient absorption spectroscopy. We show that the evolution of the band-edge bleach with increasing exciton number can be interpreted as state filling of the conduction- and valence-band edge states by delocalized electrons and holes. In line with this interpretation, net stimulated emission is observed once the average exciton number exceeds 1. We account for this lower-than-expected gain threshold and for the spectral properties of the gain band by reckoning that the Stokes shift between band-edge absorption and emission is the dominant spectral shift. The underlying exciton-phonon coupling leads to a stimulated emission mechanism, where also single excitons could lead to net optical gain. To fully profit from this advantageous stimulated emission scheme, we argue that InP/ZnSe QDs with more narrow emission lines are needed and spurious trapping of electron-hole pairs at high exciton numbers must be suppressed, for example by better controlling the composition of the core/shell interface.

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Fine Structure of Nearly Isotropic Bright Excitons in InP/ZnSe Colloidal Quantum Dots

Cited by 25 publications

References 28 publications

Exciton-phonon coupling in InP quantum dots with ZnS and (Zn,Cd)Se shells

Exciton-phonon coupling in InP quantum dots with ZnS and (Zn,Cd)Se shells

Interplay of Bright Triplet and Dark Excitons Revealed by Magneto‐Photoluminescence of Individual PbS/CdS Quantum Dots

State Filling and Stimulated Emission by Colloidal InP/ZnSe Core/Shell Quantum Dots

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