Nanocrystal Shape and the Mechanism of Exciton Spin Relaxation

Scholes, Gregory D.; Kim, Jeongho; Wong, C.; Huxter, Vanessa M.; Nair, P. Sreekumari; Fritz, Karolina P.; Kumar, Sandeep

doi:10.1021/nl061414e

Cited by 43 publications

(63 citation statements)

References 55 publications

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“…The dipole-dipole coupling approximation applies directly only to singlet exciton transfer but by virtue of the ISC, it remains valid for the description of triplet states as well [83,84,89]. The time-resolved experimental data [81] indicates that ISC between the singlet and triplet state manifolds of QDs occurs faster than the excitation transfer between the dot and the dye [28]. Therefore, one can expect an average behavior that is well represented by the present model.…”

Section: Exciton Dynamicsmentioning

confidence: 51%

“…It should be noted that due to the presence of the heavy elements, the spin-orbit interaction (SOI) plays an important role in the optical properties of QDs by mixing singlet and triplet states [81]. The strength and importance of SOI is system and size dependent.…”

Section: Electronic Structurementioning

confidence: 99%

“…The exciton radius in CdSe is smaller. SOI in CdSe QDs suppresses the singlet character of the lowest energy exciton to as low as 30% [81]. Similarly, the relatively closely spaced singlet and triplet states of the porphyrin molecule are noticeably coupled by SOI, which creates the conditions required for creation of singlet oxygen.…”

Section: Electronic Structurementioning

confidence: 99%

“…Experimental data indicates that the lowest energy exciton in CdSe QDs is a mixture of singlet and triplet states [81]. The sequence of events involving an optical excitation in the manifold of singlet states and a subsequent transfer of a singlet exciton can be enriched by intersystem crossing (ISC) and formation of a triplet exciton.…”

Section: Exciton Dynamicsmentioning

confidence: 99%

See 3 more Smart Citations

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

Kilin

Tsemekhman

Prezhdo

et al. 2007

Journal of Photochemistry and Photobiology A: Chemistry

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The observed resonance energy transfer in nanoassemblies of CdSe/ZnS quantum dots and pyridyl-substituted free-base porphyrin molecules [Zenkevich et al., J. Phys. Chem. B 109 (2005) 8679] is studied computationally by ab initio electronic structure and quantum dynamics approaches. The system harvests light in a broad energy range and can transfer the excitation from the dot through the porphyrin to oxygen, generating singlet oxygen for medical applications. The geometric structure, electronic energies, and transition dipole moments are derived by density functional theory and are utilized for calculating the Förster coupling between the excitons residing on the quantum dot and the porphyrin. The direction and rate of the irreversible exciton transfer is determined by the initial photoexcitation of the dot, the dot-porphyrin coupling and the interaction to the electronic subsystem with the vibrational environment. The simulated electronic structure and dynamics are in good agreement with the experimental data and provide real-time atomistic details of the energy transfer mechanism.

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Section: Exciton Dynamicsmentioning

confidence: 51%

Section: Electronic Structurementioning

confidence: 99%

Section: Electronic Structurementioning

confidence: 99%

Section: Exciton Dynamicsmentioning

confidence: 99%

See 2 more Smart Citations

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

Kilin

Tsemekhman

Prezhdo

et al. 2007

Journal of Photochemistry and Photobiology A: Chemistry

View full text Add to dashboard Cite

show abstract

“…See ref. [93] for parameters and methods used in the calculations (except for the nanorods, where the change in the valence band ordering is accounted for by altering the crystal field shift from À25 meV to a phenomenological value of þ25 meV). The states are indicated by their total angular momentum F, which is found as the sum of electron spin quantum numbers and the summed angular momenta of occupied orbitals for each electronic configuration.…”

Section: Feature Articlementioning

confidence: 99%

Controlling the Optical Properties of Inorganic Nanoparticles

Scholes¹

2008

Adv Funct Materials

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227

198

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The sophistication with which we can now prepare and characterize inorganic nanoparticles has inspired new areas of research into the fundamental properties and applications of these fascinating nanoscale systems. In this article some of the recent ideas concerning control of their optical properties are examined and explained, focusing on semiconductor nanocrystals. It is known that the optical properties of nanocrystals can be size‐tunable, but it is less obvious how shape matters. To explain how size as well as shape matters, the electronic structure of nanocrystals is sketched in relatively simple terms, leading to an introduction to deeper concepts at the heart of spectroscopy such as the exciton fine structure. The exciton fine structure states, although obscured by inhomogeneous line broadening, dictate selection rules for optical excitation. These viewpoints are compared and contrasted to well‐established principles in molecular spectroscopy that provide inspiration as well as perspective. The control of optical poperties is founded on our ability to prepare good quality colloidal particles. Recent advances in nanocrystal shape control are described. The current status of heterostructures is examined, with an emphasis on charge separation in CdSe–CdTe nanorods.

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Evolutionary Shape Control During Colloidal Quantum‐Dot Growth

Nair

Fritz

Scholes

2007

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Size-dependent optical properties of semiconductor nanocrystals are of great interest because of the myriad of phenomena stemming from them. The preparation of more complex colloidal shapes will facilitate the systematic study of shape-dependent phenomena. It is shown that a strategy to obtain systematically more complex nanocrystal structures is to exert a sequence of shape-directing steps during the colloidal growth. Using experiments based on multiple reagent injections we show how changes in the type of surfactant introduced during growth of CdSe nanocrystals promotes shape evolution. On this basis, we propose a means to achieve a further generation of shape design in nanometer-sized colloids by using a series of growth steps, each one building from the previous conditions of shape as well as surface-specific reactivity. To understand the shape formation and stability in nanocrystalline colloids, and particularly the importance of surface ligands, we introduce an analogy with the thermodynamics of droplets.

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Nanocrystal Shape and the Mechanism of Exciton Spin Relaxation

Cited by 43 publications

References 55 publications

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

Controlling the Optical Properties of Inorganic Nanoparticles

Evolutionary Shape Control During Colloidal Quantum‐Dot Growth

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