Anomalous Stokes shift in CdSe nanocrystals

Liptay, Thomas J.; Marshall, Lisa F.; Rao, P. Sambasiva; Ram, Rajeev J.; Bawendi, Moungi G.

doi:10.1103/physrevb.76.155314

Cited by 90 publications

(109 citation statements)

References 28 publications

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“…2,3,10,12,13,15−18 el-ph coupling is also crucial for thermal transport processes 19 and underpins the temperature dependence of both electron transport and nonradiative energy transfer processes in colloidal quantum dot (QD) superlattices. 20−22 Moreover, coupling to acoustic phonon modes determines the homogeneous linewidths of optical transitions and contributes to the resonant Stokes shift, 23 whereas coupling to longitudinal optical (LO) phonon modes has been observed to relax selection rules, yielding momentum-conserving optical transitions (i.e., phonon-assisted transitions or phonon replicas) from the so-called "dark exciton states" in semiconductor QDs and quantum rods. 24−28 Interestingly, it has been recently proposed that coupling to low energy acoustic phonons 2.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Exciton–Phonon Coupling in Colloidal Type-II CdTe-CdSe Heteronanocrystals

Groeneveld

Donegá

2012

J. Phys. Chem. C

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In this paper, the observation of LO-phonon progressions in the low temperature (4.2 K) photoluminescence excitation spectra of different types of colloidal NCs is reported. The strength of the exciton-LO-phonon coupling at 4.2 K, as reflected by the Huang−Rhys parameter S, increases from CdSe QDs (S = 0.8−1.0) to Type-I 1/2 CdTe/CdSe HNCs (S = 1.5), and from these to Type-II CdTe/CdSe HNCs (S = 2.9). This trend is explained by the decrease in the electron−hole wave function overlap that accompanies the gradual increase in the CdSe volume fraction in the HNCs. The decrease in the electron−hole overlap increases the exciton polarization, which in turn enhances the exciton-LO-phonon coupling via the Froḧlich interaction. The results provide novel insights into the nature of spatially indirect exciton transitions and show that compositional control of semiconductor heteronanocrystals can be used as a very effective tool to tailor the exciton−phonon coupling strength of nanoscale excitons.

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Section: Introductionmentioning

confidence: 99%

Enhanced Exciton–Phonon Coupling in Colloidal Type-II CdTe-CdSe Heteronanocrystals

Groeneveld

Donegá

2012

J. Phys. Chem. C

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“…Stokes shift in CdSe NP PL is thought to arise from radiative decay from either dark to bright exciton states during and after electronic level relaxation or from lower energy levels after interactions with phonons, or from both [25][26][27] . Coupling from a bound NP (acting as donor) to the SWNT (as acceptor) could be due to the dipole-dipole coupling of Förster resonance energy transfer (FRET) and/or charge transfer, including exciton transfer, or transfer of electrons and/or holes [28][29][30][31] .…”

Section: Discussionmentioning

confidence: 99%

“…This expression is appropriate for transfer between a point "dipole" and an infinitely long linear "dipole" in the dipole-dipole coupling limit (R >> r + ρ) and is used here even for R < r + ρ; this assumption is re-examined below 26,28,29 . This rate is also assumed to be independent of i (≥1).…”

Section: Relaxation Modes and Ratesmentioning

confidence: 99%

“…Figure S4 shows that the agreement improves with smaller f (0.25), but we use f = 0.5 as the base case because roughly half of this Stokes shift is usually in the vibrational manifold of the excited electronic state 26 and the fits for the NP and hybrids Stokes shifts are best for f = 0.5 (Fig. S5).…”

Section: Figures 3 and S2 Plot The Phonon Model Predictions For The Smentioning

confidence: 99%

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Anomalous photoluminescence Stokes shift in CdSe nanoparticle and carbon nanotube hybrids

Akey

Zhu

et al. 2012

Phys. Rev. B

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A very large decrease in the Stokes shift in CdSe nanoparticle photoluminescence is seen from hybrid materials in which the nanoparticles are attached to single-walled carbon nanotubes after pyridine treatment relative to unbound nanoparticles capped by pyridine. This is observed particularly for very small nanoparticles, for hybrids composed of core-only and core-shell nanoparticles, and for hybrids made with bundles of mixtures of semiconducting and metallic nanotubes or with semiconducting nanotubes only, and is likely due to fast Förster resonance energy transfer (FRET) from the nanoparticles to the nanotubes. A simple model demonstrates the plausibility of the hot luminescence explanation of this decreased Stokes shift.2

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“…[27,[83][84][85][86][87] One should note that the existence of "kink" has up to now only been reported with respect to the PL properties of QDs. Unusual "luminescence antiquenching" at a well defined temperature of T∼250 K (manifested in our experiments as "kink") has been observed for CdTe or CdSe/ZnS QDs initially dissolved in liquid solutions such as toluene, and has been related to a phase transition in the surfactant capping layer.…”

Section: Ligand Capping Phase Transitions In "Qd-dye" Nanocomposites mentioning

confidence: 99%

Ligand Exchange Dynamics and Temperature Effects upon Formation of Nanocomposites Based on Semiconductor CdSе/ZnS Quantum Dots and Porphyrins: Ensemble and Single Object Measurements

Zenkevich¹,

Blaudeck²,

Kowerko³

et al. 2012

MHC

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Dye molecules with pyridyl side substituents (porphyrins and heterocyclic perylene diimides) coordinatively attached to semiconductor CdSe/ZnS quantum dots (QDs) surface form quasi-stable "QD-Dye" nanocomposites of various geometry in the competition with capping molecules (tri-n-octyl phosphine oxide or long chain amines) exchange. This results in photoluminescence (PL) quenching of the QDs both due to Foerster resonance energy transfer and formation of non-radiative surface states. QD surface is inhomogeneous with respect to the involved attachment and detachment processes. The formation of "QD-Porphyrin" nanocomposites is realized at least two time scales (60 and 600 s), which is attributed to a reorganisation of tri-n-octylphosphine oxide capping shell. In a low temperature range of 220÷240 K related changes in QD absorption and emission reveal a phase transition of the capping shell (tri-n-octyl phosphine oxide and amine). In "QD-Dye" nanocomposites, this phase transition is enhanced considerably by only a few attached

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Anomalous Stokes shift in CdSe nanocrystals

Cited by 90 publications

References 28 publications

Enhanced Exciton–Phonon Coupling in Colloidal Type-II CdTe-CdSe Heteronanocrystals

Enhanced Exciton–Phonon Coupling in Colloidal Type-II CdTe-CdSe Heteronanocrystals

Anomalous photoluminescence Stokes shift in CdSe nanoparticle and carbon nanotube hybrids

Ligand Exchange Dynamics and Temperature Effects upon Formation of Nanocomposites Based on Semiconductor CdSе/ZnS Quantum Dots and Porphyrins: Ensemble and Single Object Measurements

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