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Related Concept Videos

¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

5.2K
When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
5.2K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

1.1K
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
1.1K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.5K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
1.5K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

1.8K
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
1.8K
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

1.3K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
1.3K
Molecular Spectroscopy: Absorption and Emission01:14

Molecular Spectroscopy: Absorption and Emission

2.4K
Molecules possess discrete energy levels called quantum states. Unlike atoms, which have simpler energy levels, molecules possess additional rotational and vibrational energy levels.  Each energy level is separated by an energy gap, with the gaps between adjacent electronic, vibrational, and rotational levels varying significantly. The three types of energy levels in a diatomic molecule are shown in Figure 1.
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Updated: Jul 23, 2025

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection
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Two Biexciton Types Coexisting in Coupled Quantum Dot Molecules.

Nadav Frenkel1, Einav Scharf2, Gur Lubin1

  • 1Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 7610001, Israel.

ACS Nano
|July 17, 2023
PubMed
Summary
This summary is machine-generated.

Coupled colloidal quantum dot molecules exhibit two biexciton species: one fast-decaying and strongly interacting, the other long-lived and weakly interacting. This finding aids in designing advanced quantum light emitters.

Keywords:
BiexcitonsBinding energyHybridizationQuantum dotsSPAD arraysSingle-particle spectroscopy

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Area of Science:

  • Nanoscience and Materials Science
  • Quantum Optics
  • Solid-State Physics

Background:

  • Coupled colloidal quantum dot molecules (CQDMs) are novel nanomaterials with two coupled emission centers, offering new possibilities for quantum technologies.
  • Understanding multiply excited states in CQDMs is vital for their application as quantum light emitters, but current spectroscopic methods are limited.

Purpose of the Study:

  • To characterize biexcitonic species in CQDMs, distinguishing between segregated and localized configurations.
  • To investigate the interplay between different biexciton states and their influence on CQDM properties.

Main Methods:

  • Extension of Heralded Spectroscopy to resolve distinct biexciton species in CdSe/CdS CQDMs.
  • Comparative analysis of CQDMs, single quantum dots, and nonfused quantum dot pairs.
  • Numerical simulations to validate experimental findings.

Main Results:

  • Identification of two coexisting biexciton species in CQDMs: a fast-decaying, strongly interacting type and a long-lived, weakly interacting type.
  • The strongly interacting species resembles biexcitons in single quantum dots, while the weakly interacting species involves nearly independent excitons.
  • Experimental results are consistent with simulations, attributing the species to localized or segregated exciton configurations within the CQDM.

Conclusions:

  • The study reveals distinct biexciton behaviors in CQDMs, crucial for understanding their quantum emission properties.
  • This work provides insights into the localization and segregation of excitons, enabling the design of CQDMs with tailored optical characteristics.
  • The findings support the rational design of tunable single- and multiple-photon quantum emitters based on CQDMs.