Type-II Quantum Dots:  CdTe/CdSe(Core/Shell) and CdSe/ZnTe(Core/Shell) Heterostructures

Kim, Sungjee; Fisher, Brent; Eisler, Hans‐Jürgen; Bawendi, Moungi G.

doi:10.1021/ja0361749

Cited by 1,214 publications

(1,219 citation statements)

References 25 publications

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“…33 This will reduce the fidelity of spike detection since in the optical shotnoise-limited regime this fidelity scales as the square root of the fluorescence intensity. 34 In principle, the lower quantum yield value can be offset with higher excitation intensity.…”

Section: Voltage Sensitivity Of Type-ii Semiconductor Nanoparticlesmentioning

confidence: 99%

“…This enhancement is, however, very sensitive on the amplitude of the valence band offset between CdTe and ZnTe, which varies between preparations. 25,33 Other heterostructures, with valence band offsets yielding more confined and less polarizable holes, such as CdTe-CdS and CdTe-CdSe, displayed more modest increases in dynamic range.We note that heterostructures typically have low quantum yields (~5%), due to the restricted spatial overlap between the carrier wave functions, as compared to >50% for core-shell nanocrystals. 33 This will reduce the fidelity of spike detection since in the optical shotnoise-limited regime this fidelity scales as the square root of the fluorescence intensity.…”

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confidence: 99%

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Optical Strategies for Sensing Neuronal Voltage Using Quantum Dots and Other Semiconductor Nanocrystals

Marshall

Schnitzer

2013

ACS Nano

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Biophysicists have long sought optical methods capable of reporting the electrophysiological dynamics of large-scale neural networks with millisecond-scale temporal resolution. Existing fluorescent sensors of cell membrane voltage can report action potentials in individual cultured neurons, but limitations in brightness and dynamic range of both synthetic organic and genetically encoded voltage sensors have prevented concurrent monitoring of spiking activity across large populations of individual neurons. Here we propose a novel, inorganic class of fluorescent voltage sensors: semiconductor nanoparticles, such as ultrabright quantum dots (qdots). Our calculations revealed that transmembrane electric fields characteristic of neuronal spiking (~10 mV/nm) modulate a qdot's electronic structure and can induce ~5% changes in its fluorescence intensity and ~1 nm shifts in its emission wavelength, depending on the qdot's size, composition, and dielectric environment. Moreover, tailored qdot sensors composed of two different materials can exhibit substantial (~30%) changes in fluorescence intensity during neuronal spiking. Using signal detection theory, we show that conventional qdots should be capable of reporting voltage dynamics with millisecond precision across several tens or more individual neurons over a range of optical and neurophysiological conditions. These results unveil promising avenues for imaging spiking dynamics in neural networks and merit in-depth experimental investigation. Toward addressing these challenges, we studied whether tools from nanotechnology, specifically, bright, multifunctional semiconductor quantum dots (qdots), 22,23 might be useful for imaging neuronal membrane potentials. Qdots are known to possess voltagesensitive optical properties, including a red-shifting of the qdot's fluorescence emission peak, spectral broadening, and a decrease in the intensity of fluorescence emission ( Figure 1C,D). [24][25][26][27] Qdots also are highly resistant to photobleaching and exhibit large quantum yields and absorption cross sections for one-(σ 1 ) and two-photon (σ 2 ) excitation. For example, CdSe qdots with radius R ~ 3 nm exhibit cross sections of σ 1 > 1 nm 2 and σ 2 > 3 × 10 4 GM, as compared to σ 1 ~ 10 −2 nm 2 and σ 2 ~ 3 × 10 2 GM for green fluorescent protein. 28,29 Marshall and Schnitzer Page 2 ACS Nano. Author manuscript; available in PMC 2017 December 15. Graphical Abstract HHMI Author Manuscript HHMI Author Manuscript HHMI Author ManuscriptTo evaluate the spike detection capabilities of qdot indicators quantitatively, we applied a theoretical approach that incorporates the physical, biophysical, and statistical components of the problem. We calculated the effect of applied electric fields on the qdot's electronic structure and examined how this modulates a qdot's fluorescence intensity and emission spectra. We also studied nonspherical, nonhomogenous qdots, which we refer to more generally as semiconductor nanocrystals, and found that these nanoparticles can demonstrate muc...

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Section: Voltage Sensitivity Of Type-ii Semiconductor Nanoparticlesmentioning

confidence: 99%

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confidence: 99%

Optical Strategies for Sensing Neuronal Voltage Using Quantum Dots and Other Semiconductor Nanocrystals

Marshall

Schnitzer

2013

ACS Nano

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“…For example, in PbS QDSCs, the fast exciton recombination limits the photon‐to‐power conversion efficiency (PCE), which is less than 12%, well below typical values of commercial silicon solar cells (in general around 20%) and its theoretical value (44% in QDSCs) 3. The synthesis of heterostructured QDs and tailoring of their composition/shape are shown to be an efficient approach to control exciton and charge carrier dynamics 4. For instance, heterostructured tetrapod‐shaped QDs (PbSe/CdSe/CdS QDs), which are nonspherical, can favor the spatial separation of electron–hole wave functions, resulting in long radiative lifetime that facilitates charge extraction and transport.…”

Section: Introductionmentioning

confidence: 99%

Optoelectronic Properties in Near‐Infrared Colloidal Heterostructured Pyramidal “Giant” Core/Shell Quantum Dots

et al. 2018

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Colloidal heterostructured quantum dots (QDs) are promising candidates for next‐generation optoelectronic devices. In particular, “giant” core/shell QDs (g‐QDs) can be engineered to exhibit outstanding optical properties and high chemical/photostability for the fabrication of high‐performance optoelectronic devices. Here, the synthesis of heterostructured CuInSexS2− x (CISeS)/CdSeS/CdS g‐QDs with pyramidal shape by using a facile two‐step method is reported. The CdSeS/CdS shell is demonstrated to have a pure zinc blend phase other than typical wurtzite phase. The as‐obtained heterostructured g‐QDs exhibit near‐infrared photoluminescence (PL) emission (≈830 nm) and very long PL lifetime (in the microsecond range). The pyramidal g‐QDs exhibit a quasi‐type II band structure with spatial separation of electron–hole wave function, suggesting an efficient exciton extraction and transport, which is consistent with theoretical calculations. These heterostructured g‐QDs are used as light harvesters to fabricate a photoelectrochemical cell, exhibiting a saturated photocurrent density as high as ≈5.5 mA cm−2 and good stability under 1 sun illumination (AM 1.5 G, 100 mW cm−2). These results are an important step toward using heterostructured pyramidal g‐QDs for prospective applications in solar technologies.

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“…It is possible to engineer core-shell quantum dots [34,35], for example of type II with a CdTe core and a CdSe shell or a CdSe core and a ZnTe shell [35]. We apply our method to such a type II quantum dot with a CdSe core (a) The inset shows the band structure of a type II quantum dot of CdSe with a ZnTe shell in the case of an applied electric field.…”

Section: Resultsmentioning

confidence: 99%

Förster Coupling in Nanoparticle Excitonic Circuits

2010

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Exciton transport in semiconductor nanoparticles underlies recent experiments on electrically controlled excitonic circuits and proposals for new artificial light-harvesting systems. In this work, we develop a new method for the numerical evaluation of the Förster matrix element, based on a three-dimensional real space grid and the self-consistent solution of the mesoscopic exciton in a macroscopic dielectric environment. This method enables the study of the role of the nanoparticle shape, spatially varying dielectric environment, and externally applied electric fields. Depending on the orientation of the transition dipole, the Förster coupling is shown to be either increased or decreased as a function of the nanoparticle shape and of the properties of the dielectric environment. In the presence of an electric field, we investigate the relation between excitonic binding and confinement effects. We also study a type II core-shell quantum dot where electron and hole are spatially separated due to a particular configuration of the bandstructure.

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Type-II Quantum Dots: CdTe/CdSe(Core/Shell) and CdSe/ZnTe(Core/Shell) Heterostructures

Cited by 1,214 publications

References 25 publications

Optical Strategies for Sensing Neuronal Voltage Using Quantum Dots and Other Semiconductor Nanocrystals

Optical Strategies for Sensing Neuronal Voltage Using Quantum Dots and Other Semiconductor Nanocrystals

Optoelectronic Properties in Near‐Infrared Colloidal Heterostructured Pyramidal “Giant” Core/Shell Quantum Dots

Förster Coupling in Nanoparticle Excitonic Circuits

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