Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots

Brodu, Annalisa; Ballottin, Mariana V.; Buhot, Jonathan; Harten, Elleke J van; Dupont, Dorian; Porta, Andrea La; Prins, P. Tim; Tessier, Martine; Versteegh, Marijn A. M.; Zwiller, Val; Bals, Sara; Hens, Zeger; Rabouw, Freddy T.; Christianen, Peter C. M.; Donegá, Celso de Mello; Vanmaekelbergh, Daniël

doi:10.1021/acsphotonics.8b00615

Cited by 48 publications

(87 citation statements)

References 62 publications

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“…However, in the case of InP/ZnSe QDs emitting at a similar photon energy as the QDs studied here, the dark exciton was only observed through a broad, phonon-coupled emission feature shifted 5-15 meV to the red of the bright exciton. 13 Clearly, this observation supports the assignment of the high energy doublet in the case of InP/ZnSe QDs to a bright exciton doublet rather than a bright-dark combination. Possibly, the combination of strong broadening and long radiative lifetimes makes the dark exciton indiscernible in the emission spectrum of single InP/ZnSe QDs.…”

supporting

confidence: 80%

“…To determine the overall degeneracy of the bright exciton -2-fold with a minor splitting due to anisotropy in the xy plane or 3-fold with a minor splitting due to anisotropy along the quantization axis z, see Figure 5 -we analyzed the emission of an ensemble of InP/ZnSe The three broad features labelled C, D and E in the FLN spectrum were assigned previously to (C) the phonon activated dark exciton emission, and replicas of this transition involving the additional emission of (D) ZnSe or (E) InP LO phonons. 13 Using the latter two as a yardstick, we estimate the bright-dark splitting in these InP/ZnSe QDs at ∆E bd = 6 meV (see Figure 6a). In Figure 6b, we show the low energy part of various FLN spectra obtained on the same InP/ZnSe QD ensemble, while increasing the magnetic field from 10 to 30 T.…”

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confidence: 99%

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

Brodu

Chandrasekaran

Scarpelli

et al. 2019

J. Phys. Chem. Lett.

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The fine structure of exciton states in colloidal quantum dots (QDs) results from the compound effect of anisotropy and electron-hole exchange. By means of single-dot photoluminescence spectroscopy, we show that the emission of photo-excited InP/ZnSe QDs originates from radiative recombination of such fine-structure exciton states. Depending on the excitation power, we identify a bright exciton doublet, a trion singlet and a biexciton doublet line that all show a pronounced polarization. Fluorescence line 1 narrowing spectra of an ensemble of InP/ZnSe QDs in magnetic fields demonstrate that the bright exciton effectively consists of three states. The Zeeman splitting of these states is well described by an isotropic exciton model, where the fine structure is dominated by electron-hole exchange and shape anisotropy only leads to a minor splitting of the F = 1 triplet. We argue that excitons in InP-based QDs are nearly isotropic because the particular ratio of light and heavy hole masses in InP makes the exciton fine structure insensitive to shape anisotropy.

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confidence: 80%

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confidence: 99%

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

Brodu

Chandrasekaran

Scarpelli

et al. 2019

J. Phys. Chem. Lett.

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“…Figure 1a shows an overview transmission electron microscopy image (TEM) of the InP/ZnSe core/shell QDs (sample A). Similar to previously published TEM images, 21,32 we obtained somewhat faceted nanocrystals that can be described in essence as quasi-spheres, see Supporting Information S1 for an overview of average sizes. The absorbance spectrum of these InP/ZnSe QDs, as plotted in Figure 1b, exhibits three readily observable features.…”

Section: Materials Propertiessupporting

confidence: 83%

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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“…In traditional type-I QDs, a low bandgap core material is coated with a second semiconductor with a wider bandgap than the core material with higher energy valence and conduction band offsets (Chandrasekaran et al, 2017 ; Brodu et al, 2018 ). Sufficiently large core size allows both the electron and hole to reside within the core, constituting the so-called type-I localization regime.…”

Section: Introductionmentioning

confidence: 99%

Bandgap Engineering of Indium Phosphide-Based Core/Shell Heterostructures Through Shell Composition and Thickness

et al. 2018

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The large bulk bandgap (1.35 eV) and Bohr radius (~10 nm) of InP semiconductor nanocrystals provides bandgap tunability over a wide spectral range, providing superior color tuning compared to that of CdSe quantum dots. In this paper, the dependence of the bandgap, photoluminescence emission, and exciton radiative lifetime of core/shell quantum dot heterostructures has been investigated using colloidal InP core nanocrystals with multiple diameters (1.5, 2.5, and 3.7 nm). The shell thickness and composition dependence of the bandgap for type-I and type-II heterostructures was observed by coating the InP core with ZnS, ZnSe, CdS, or CdSe through one to ten iterations of a successive ion layer adsorption and reaction (SILAR)-based shell deposition. The empirical results are compared to bandgap energy predictions made with effective mass modeling. Photoluminescence emission colors have been successfully tuned throughout the visible and into the near infrared (NIR) wavelength ranges for type-I and type-II heterostructures, respectively. Based on sizing data from transmission electron microscopy (TEM), it is observed that at the same particle diameter, average radiative lifetimes can differ as much as 20-fold across different shell compositions due to the relative positions of valence and conduction bands. In this direct comparison of InP/ZnS, InP/ZnSe, InP/CdS, and InP/CdSe core/shell heterostructures, we clearly delineate the impact of core size, shell composition, and shell thickness on the resulting optical properties. Specifically, Zn-based shells yield type-I structures that are color tuned through core size, while the Cd-based shells yield type-II particles that emit in the NIR regardless of the starting core size if several layers of CdS(e) have been successfully deposited. Particles with thicker CdS(e) shells exhibit longer photoluminescence lifetimes, while little shell-thickness dependence is observed for the Zn-based shells. Taken together, these InP-based heterostructures demonstrate the extent to which we are able to precisely tailor the material properties of core/shell particles using core/shell dimensions and composition as variables.

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Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots

Cited by 48 publications

References 62 publications

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

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

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

Bandgap Engineering of Indium Phosphide-Based Core/Shell Heterostructures Through Shell Composition and Thickness

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