Optically Detected Magnetic Resonance Studies of Colloidal Semiconductor Nanocrystals

Lifshitz, Efrat; Fradkin, Leonid; Glozman, A.; Langof, L.

doi:10.1146/annurev.physchem.55.091602.094359

Cited by 44 publications

(57 citation statements)

References 155 publications

(143 reference statements)

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“…(1)]; so, in our case, this is determined by the free parameter g ex . The value found for g ex is larger than that reported in the literature, 24,30,31 but close to the theoretically expected value |g ex | ≈ 4 for the dark exciton ground state. Figure 5 demonstrates that this model qualitatively explains the behavior of the PL decay times in CdTe NQDs as a function of the magnetic field.…”

Section: Discussionsupporting

confidence: 75%

Exciton lifetimes of CdTe nanocrystal quantum dots in high magnetic fields

et al. 2011

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We have measured the low-temperature (4.2 K) exciton lifetimes of zinc-blende CdTe nanocrystal quantum dots (NQDs), 2.6-3.8 nm in diameter, in magnetic fields up to 30 T. The exciton photoluminescence decay time decreases with both dot size and magnetic field. We explain the decrease in decay time in magnetic fields by the mixing of bright and dark exciton states due to a small shape asymmetry in the zinc-blende CdTe NQDs. We show that this behavior resembles that of wurtzite CdSe NQDs, and we demonstrate that an asymmetry of NQDs caused by either shape or crystal structure leads to similar exciton decay dynamics.

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Section: Discussionsupporting

confidence: 75%

Exciton lifetimes of CdTe nanocrystal quantum dots in high magnetic fields

et al. 2011

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“…A large exchange interaction would shift considerably the singlet EHP energy state with respect to the triplet and would result in two distinguished spin 1/2 magnetic resonance peaks [30]. This is not observed in our samples.…”

mentioning

confidence: 58%

“…[7,30], we can describe the dynamics of our spin system in the postpulse recovery using the following rate equations: …”

mentioning

confidence: 99%

Time-resolved spin processes inAlq3light-emitting diodes

Comandè

Ansermet

2014

Phys. Rev. B

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Using pulsed electroluminescence detected magnetic resonance (PELDMR), we study the dynamics of spin processes in Alq 3 based light-emitting diodes. The transitions induced by magnetic resonance are found to be much faster than the space charge reaction time that is measured by looking at the electroluminescence frequency response to an ac bias voltage. This observation excludes a change in the equilibrium space charge distributions as the cause of PELDMR, in favor of a change of the electron-hole recombination rate. At low temperatures the effect of electron spin resonance on the electroluminescence changes sign and lasts longer. The postpulse electroluminescence recovery is well fitted by a biexponential function characterized by two very different time scales, which are consistent with a detailed balance for the singlet and triplet states, in conformity with the electron-hole pair model.

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“…[176] Coherent pulsed optically or electrically detected magnetic resonance could offer a unique route to accessing charge localization dynamics in nanostructured materials, such as semiconductor nanocrystal quantum dots. [177] In such compounds, charge trapping can give rise to a range of dynamic optical and electrical effects, the most prominent of which is known as luminescence blinking [178] (the microscopic origins of blinking-charge separation-have been studied in depth in single organic molecules using spin resonance techniques [179] ). Recombination in quantum dot materials such as CdSe is inherently spin dependent, and leads to a range of remarkable fluorescence dynamics.…”

Section: Open Questionsmentioning

confidence: 99%

Coherent Spin Manipulation in Molecular Semiconductors: Getting a Handle on Organic Spintronics

Lupton¹,

McCamey²,

Boehme³

2010

ChemPhysChem

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Organic semiconductors offer expansive grounds to explore fundamental questions of spin physics in condensed matter systems. With the emergence of organic spintronics and renewed interest in magnetoresistive effects, which exploit the electron spin degree of freedom to encode and transmit information, there is much need to illuminate the underlying properties of spins in molecular electronic materials. For example, one may wish to identify over what length of time a spin maintains its orientation with respect to an external reference field. In addition, it is crucial to understand how adjacent spins arising, for example, in electrostatically coupled charge‐carrier pairs, interact with each other. A periodic perturbation of the field may cause the spins to precess or oscillate, akin to a spinning top experiencing a torque. The quantum mechanical characteristic of the spin is then defined as the coherence time, the time over which an oscillating spin, or spin pair, maintains a fixed phase with respect to the driving field. Electron spins in organic semiconductors provide a remarkable route to performing “hands‐on” quantum mechanics since permutation symmetries are controlled directly. Herein, we review some of the recent advances in organic spintronics and organic magnetoresistance, and offer an introductory description of the concept of pulsed, electrically detected magnetic resonance as a technique to manipulate and thus characterize the fundamental properties of electron spins. Spin‐dependent dissociation and recombination allow the observation of coherent spin motion in a working device, such as an organic light‐emitting diode. Remarkably, it is possible to distinguish between electron and hole spin resonances. The ubiquitous presence of hydrogen nuclei gives rise to strong hyperfine interactions, which appear to provide the basis for many of the magnetoresistive effects observed in these materials. Since hyperfine coupling causes quantum spin beating in electron–hole pairs, an extraordinarily sensitive probe for hyperfine fields in such pairs is given.

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Optically Detected Magnetic Resonance Studies of Colloidal Semiconductor Nanocrystals

Cited by 44 publications

References 155 publications

Exciton lifetimes of CdTe nanocrystal quantum dots in high magnetic fields

Exciton lifetimes of CdTe nanocrystal quantum dots in high magnetic fields

Time-resolved spin processes inAlq3light-emitting diodes

Coherent Spin Manipulation in Molecular Semiconductors: Getting a Handle on Organic Spintronics

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