Controlling the Surface of Semiconductor Nanocrystals for Efficient Light Emission from Single Excitons to Multiexcitons

Walsh, Brenna; Saari, Jonathan I.; Krause, Michael; Nick, Robert; Coe‐Sullivan, Seth; Kambhampati, Patanjali

doi:10.1021/acs.jpcc.5b03853

Cited by 17 publications

(27 citation statements)

References 33 publications

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“…To our knowledge, this marks the first time that two distinct LO phonons (i.e., phonons coupled to two different excitonic transitions) have been identified in multidimensional spectra of CdSe QDs. The features described here are distinct from the LO phonon peak structure reported elsewhere 38 that is often attributed to the surface-optical phonon; 39 the electronic correlation information afforded by GAMERS is necessary to isolate these transitions. Based on an analysis of the available coherence pathways (see SI), we note that the X 1 -coupled LO peak includes contributions from both ground and excited electronic state pathways during T, while the X 2 -coupled LO peak exclusively contains ground state pathways.…”

Section: The Journal Of Physical Chemistry Lettersmentioning

confidence: 59%

Exciton–Phonon Spectroscopy of Quantum Dots Below the Single-Particle Homogeneous Line Width

Spencer

Hutson

Irgen-Gioro

et al. 2018

J. Phys. Chem. Lett.

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We demonstrate that high-dimensionality coherent spectroscopy yields "super-resolved" spectra whereby peaks may be localized far below their homogeneous line width by resolving them across multiple, coherently coupled dimensions. We implement this technique using a fifth-order photon-echo spectroscopy called Gradient-Assisted Multidimensional Electronic-Raman Spectroscopy (GAMERS) that combines resonant and nonresonant excitation to disperse the optical response across three spectral dimensions: two involving excitonic transitions and one that encodes phonon energies. In analogy to super-resolution localization microscopies, which separate spatially overlapping signals in time, GAMERS isolates signals spectrally using combined electronic and nuclear resolution. Optical phonon lines in a colloidal solution of CdSe quantum dots at room temperature separated by less than 150 μeV are resolved despite the homogeneous line width of these transitions being nearly an order of magnitude broader. The frequency difference between these phonon modes is attributed to softening of the longitudinal phonon mode upon excitation to the lowest exciton state. Further, such phonon mode selectivity yields spectra with electronic line widths that approach the single particle limit. Through this enhanced spectral resolution, the GAMERS method yields insights into the nature of coupling between longitudinal optical and acoustic phonons and specific excitonic transitions that were previously hidden.

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Section: The Journal Of Physical Chemistry Lettersmentioning

confidence: 59%

Exciton–Phonon Spectroscopy of Quantum Dots Below the Single-Particle Homogeneous Line Width

Spencer

Hutson

Irgen-Gioro

et al. 2018

J. Phys. Chem. Lett.

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“…Chemical functionalization of the QD surface is a powerful and versatile strategy to tune the energies and spatial distributions of core and surface states of colloidal QDs because the surface ligands control (i) the degree of surface enrichment of cations or anions, − (ii) the degree of coordination of surface ions (how electron rich or electron poor they are), − (iii) in some cases, the magnitude of the confinement energy of excitonic charge carriers, − and (iv) the crystal structure and the size of QDs, when those ligands are present as surfactant in the reaction mixture. − Common protocols to prepare colloidal QDs ,,− produce QDs terminated with aliphatic organic molecules, such as alkyl carboxylates, alkyl phosphonates, or alkylamines. With dependence on the particular application of the QDs, these ligands can be replaced after synthesis with a large variety of organic molecules, ,,− in order to tune the electronic structure of the nanoscale interface and, in some cases, the electronic structure of the QD’s core.…”

Section: Role Of Molecules In the Electronic Structure Of Colloidal Qdsmentioning

confidence: 99%

Electronic Processes within Quantum Dot-Molecule Complexes

et al. 2016

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The subject of this review is the colloidal quantum dot (QD) and specifically the interaction of the QD with proximate molecules. It covers various functions of these molecules, including (i) ligands for the QDs, coupled electronically or vibrationally to localized surface states or to the delocalized states of the QD core, (ii) energy or electron donors or acceptors for the QDs, and (iii) structural components of QD assemblies that dictate QD-QD or QD-molecule interactions. Research on interactions of ligands with colloidal QDs has revealed that ligands determine not only the excited state dynamics of the QD but also, in some cases, its ground state electronic structure. Specifically, the article discusses (i) measurement of the electronic structure of colloidal QDs and the influence of their surface chemistry, in particular, dipolar ligands and exciton-delocalizing ligands, on their electronic energies; (ii) the role of molecules in interfacial electron and energy transfer processes involving QDs, including electron-to-vibrational energy transfer and the use of the ligand shell of a QD as a semipermeable membrane that gates its redox activity; and (iii) a particular application of colloidal QDs, photoredox catalysis, which exploits the combination of the electronic structure of the QD core and the chemistry at its surface to use the energy of the QD excited state to drive chemical reactions.

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“…25 Ultrafast pump/probe spectroscopy is a better measurement in that it can be used to extract and disentangle average exciton populations, gain thresholds, lifetimes, and crosssections. State-resolved pump/probe will further reveal state specificity to key processes, such as control over gain bandwidth, 26,27 and enable the measurement of biexciton level structure. 28,29 Semiconductor NCs have a number of favorable characteristics as an optical gain medium, but no single platform exists with ideal performance in all respects.…”

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confidence: 99%

Efficient Optical Gain in CdSe/CdS Dots-in-Rods

et al. 2018

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Excitonic-state-resolved pump/probe spectroscopy is performed on semiconductor dot-in-rod nanocrystals. Using excitonic-state-resolved pumping we are able to resolve effects of the rod upon exciton dynamics of the core. The shell has the effect of lowering gain threshold, increasing absorption cross-section, and increasing the Auger lifetime; hence nanorods are shown to be an effective means of enhancing gain performance of nanomaterials.

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Controlling the Surface of Semiconductor Nanocrystals for Efficient Light Emission from Single Excitons to Multiexcitons

Cited by 17 publications

References 33 publications

Exciton–Phonon Spectroscopy of Quantum Dots Below the Single-Particle Homogeneous Line Width

Exciton–Phonon Spectroscopy of Quantum Dots Below the Single-Particle Homogeneous Line Width

Electronic Processes within Quantum Dot-Molecule Complexes

Efficient Optical Gain in CdSe/CdS Dots-in-Rods

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