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Tycko, Robert; Dabbagh, G.; Kurtz, Sarah; Goral, J.P.

doi:10.1103/physrevb.75.249901

Cited by 7 publications

(25 citation statements)

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“…5 Å of one another). The intense 31 P NMR signal centered at −164 ppm is attributed to P atoms residing in the phosphide core of InP and In 0.50 Ga 0.50 P because this peak has the highest intensity in the spin-echo spectrum, and a similar chemical shift was reported in prior studies of InP and In 1– x Ga x P phases. − There is one additional 31 P NMR signal at ca. −119 ppm observed in the spectrum of the InP QDs next to the most intense 31 P NMR signal, which is assigned to subsurface phosphide 31 P atoms .…”

Section: Resultssupporting

confidence: 54%

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In_1–xGa_xP/ZnS Colloidal Quantum Dots

et al. 2023

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Semiconductors are commonly divided into materials with direct or indirect band gaps based on the relative positions of the top of the valence band and the bottom of the conduction band in crystal momentum (k) space. It has, however, been debated if k is a useful quantum number to describe the band structure in quantum-confined nanocrystalline systems, which blur the distinction between direct and indirect gap semiconductors. In bulk III−V semiconductor alloys like In 1−x Ga x P, the band structure can be tuned continuously from the direct-to indirect-gap by changing the value of x. The effect of strong quantum confinement on the direct-to-indirect transition in this system has yet to be established because high-quality colloidal nanocrystal samples have remained inaccessible. Herein, we report one of the first systematic studies of ternary III−V nanocrystals by utilizing an optimized molten-salt In-to-Ga cation exchange protocol to yield bright In 1−x Ga x P/ZnS core−shell particles with photoluminescence quantum yields exceeding 80%. We performed two-dimensional solid-state NMR studies to assess the alloy homogeneity and the extent of surface oxidation in In 1−x Ga x P cores. The radiative decay lifetime for In 1−x Ga x P/ZnS monotonically increases with higher gallium content. Transient absorption studies on In 1−x Ga x P/ZnS nanocrystals demonstrate signatures of direct-and indirect-like behavior based on the presence or absence, respectively, of excitonic bleach features. Atomistic electronic structure calculations based on the semi-empirical pseudopotential model are used to calculate absorption spectra and radiative lifetimes and evaluate band-edge degeneracy; the resulting calculated electronic properties are consistent with experimental observations. By studying photoluminescence characteristics at elevated temperatures, we demonstrate that a reduced lattice mismatch at the III−V/II−VI core−shell interface can enhance the thermal stability of emission. These insights establish cation exchange in molten inorganic salts as a viable synthetic route to nontoxic, high-quality In 1−x Ga x P/ZnS QD emitters with desirable optoelectronic properties.

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Section: Resultssupporting

confidence: 54%

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In_1–xGa_xP/ZnS Colloidal Quantum Dots

et al. 2023

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“…The comparison of the experimentally observed populations (Figure a, dots) with the populations resulting for a random distribution (Figure a, dashed lines) shows an overall good agreement, with small but systematic deviations especially for the mixed contact MA–FA (red). This indicates a weak tendency for clustering of MA and FA cations, leading to local fluctuations in composition, which can be quantified by introducing an order parameter S , − in analogy to the analysis of XRD data . For a cluster model, an order parameter of S = 0 corresponds to a random distribution, whereas S = 1 characterizes a complete phase separation.…”

Section: Resultsmentioning

confidence: 99%

Microscopic (Dis)order and Dynamics of Cations in Mixed FA/MA Lead Halide Perovskites

Grüninger¹,

Bokdam

Leupold

et al. 2021

J. Phys. Chem. C

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Recent developments in the field of high efficiency perovskite solar cells are based on stabilization of the perovskite crystal structure of FAPbI 3 while preserving its excellent optoelectronic properties. Compositional engineering of, for example, MA or Br mixed into FAPbI 3 results in the desired effects, but detailed knowledge of local structural features, such as local (dis)order or cation interactions of formamidinium (FA) and methylammonium (MA), is still limited. This knowledge is, however, crucial for their further development. Here, we shed light on the microscopic distribution of MA and FA in mixed perovskites MA 1– x FA x PbI 3 and MA 0.15 FA 0.85 PbI 2.55 Br 0.45 by combining high-resolution double-quantum 1 H solid-state nuclear magnetic resonance (NMR) spectroscopy with state-of-the-art near-first-principles accuracy molecular dynamics (MD) simulations using machine-learning force-fields (MLFFs). We show that on a small local scale, partial MA and FA clustering takes place over the whole MA/FA compositional range. A reasonable driving force for the clustering might be an increase of the dynamical freedom of FA cations in FA-rich regions. While MA 0.15 FA 0.85 PbI 2.55 Br 0.45 displays similar MA and FA ordering as the MA 1– x FA x PbI 3 systems, the average cation–cation interaction strength increased significantly in this double mixed material, indicating a restriction of the space accessible to the cations or their partial immobilization upon Br – incorporation. Our results shed light on the heterogeneities in cation composition of mixed halide perovskites, helping to exploit their full optoelectronic potential.

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“…All experiments, including transmission electron microscopy (TEM), [1−3] atomic force microscopy, [4,5] electron diffraction, [2] x-ray diffraction (XRD) [2,6,7] and nuclear magnetic resonance (NMR) [8,9] demonstrated that in A x B 1−x C epilayers A and B atoms on their group III sublattices often show spontaneously partially ordered structure because of surface-induced effects. [10,11] In partially ordered domains of A x B 1−x C epilayers, as shown in Fig.…”

Section: Various Epitaxial Techniques Have Been Utilizedmentioning

confidence: 99%

Relations between compositional modulation and atomic ordering degree in thin films of ternary III–V semiconductor alloys

Zhang

Liang

et al. 2008

Chinese Phys. B

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Erratum: Quantitative study of atomic ordering inGa0.5In0.5Pthin films byP

Abstract: In Eq. ͑1͒, the expression for A 2 should be Fig. 4a, curves labeled n = 3 and n = 1 should be exchanged, and curves labeled n = 4 and n = 0 should be exchanged. These corrections have no effect on the conclusions of this paper.

Cited by 7 publications

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Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In_1–xGa_xP/ZnS Colloidal Quantum Dots

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In_1–xGa_xP/ZnS Colloidal Quantum Dots

Microscopic (Dis)order and Dynamics of Cations in Mixed FA/MA Lead Halide Perovskites

Relations between compositional modulation and atomic ordering degree in thin films of ternary III–V semiconductor alloys

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Erratum: Quantitative study of atomic ordering inGa0.5In0.5Pthin films byP

Abstract: In Eq. ͑1͒, the expression for A 2 should be Fig. 4a, curves labeled n = 3 and n = 1 should be exchanged, and curves labeled n = 4 and n = 0 should be exchanged. These corrections have no effect on the conclusions of this paper.

Cited by 7 publications

References 0 publications

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In1–xGaxP/ZnS Colloidal Quantum Dots

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In1–xGaxP/ZnS Colloidal Quantum Dots

Microscopic (Dis)order and Dynamics of Cations in Mixed FA/MA Lead Halide Perovskites

Relations between compositional modulation and atomic ordering degree in thin films of ternary III–V semiconductor alloys

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Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In_1–xGa_xP/ZnS Colloidal Quantum Dots

Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core–Shell In_1–xGa_xP/ZnS Colloidal Quantum Dots