Optical Properties and Exciton Dynamics of Alloyed Core/Shell/Shell Cd1–xZnxSe/ZnSe/ZnS Quantum Dots

Fitzmorris, Bob C.; Pu, Ying‐Chih; Cooper, Jason K.; Lin, Yi Fang; Hsu, Yung‐Jung; Li, Yat; Zhang, Jin Z.

doi:10.1021/am303149r

Cited by 82 publications

(64 citation statements)

References 35 publications

(66 reference statements)

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“…SVD global fitting [32][33][34] was also used to analyze the TA data for each of the four samples. Each contour plot, consisting of dA as a function of both delay time and wavelength, was fitted with three exponential lifetimes, which describe the decay of the TA signal over time for each wavelength.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast Transient Absorption Studies of Hematite Nanoparticles: The Effect of Particle Shape on Exciton Dynamics

et al. 2013

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Much progress has been made in using hematite (α‐Fe2O3) as a potentially practical and sustainable material for applications such as solar‐energy conversion and photoelectrochemical (PEC) water splitting; however, recent studies have shown that the performance can be limited by a very short charge‐carrier diffusion length or exciton lifetime. In this study, we performed ultrafast studies on hematite nanoparticles of different shapes to determine the possible influence of particle shape on the exciton dynamics. Nanorice, multifaceted spheroidal nanoparticles, faceted nanocubes, and faceted nanorhombohedra were synthesized and characterized by using SEM and XRD techniques. Their exciton dynamics were investigated by using femtosecond transient absorption (TA) spectroscopy. Although the TA spectral features differ for the four samples studied, their decay profiles are similar, which can be fitted with time constants of 1–3 ps, approximately 25 ps, and a slow nanosecond component extending beyond the experimental time window that was measured (2 ns). The results indicate that the overall exciton lifetime is weakly dependent on the shape of the hematite nanoparticles, even though the overall optical absorption and scattering are influenced by the particle shape. This study suggests that other strategies need to be developed to increase the exciton lifetime or to lengthen the exciton diffusion length in hematite nanostructures.

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Section: Resultsmentioning

confidence: 99%

Ultrafast Transient Absorption Studies of Hematite Nanoparticles: The Effect of Particle Shape on Exciton Dynamics

et al. 2013

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“…Cation exchange was used to increase the bandgap and passivate trap states on the QD surface to increase PLQY. (De Trizio et al 2012;Fitzmorris et al 2013) By exchanging the surface copper and indium ions with zinc, the surface composition shifts to ZnS which facilitates the subsequent epitaxial growth of the ZnS shell (Van Embden et al 2007). The core CIS QDs were grown with an excess of the sulfur source, DPPS, which could allow some shell growth during the cation exchange step, although previous studies have shown that excess sulfur is not needed during cation exchange (Park and Kim 2011).…”

Section: Cation Exchange and Shell Growthmentioning

confidence: 99%

“…A good quality ZnS shell can be grown on the exposed CIS surfaces due to the small lattice mismatch between the two materials. ZnS shells have been shown to increase PLQY by passivating surface trap states on a range of QD systems including CdSe, CdZnSe, and CIS (Dabbousi et al 1997;Fitzmorris et al 2013;Li et al 2011;Park and Kim 2011;Speranskaya et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Structural and optical characterization of CuInS2 quantum dots synthesized by microwave-assisted continuous flow methods

et al. 2015

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Semiconductor quantum dots (QDs) have recently been incorporated into consumer displays and lighting technologies. Now that these materials are being produced on industrial scales, it is important to investigate scalable synthetic methods and less toxic materials and chemistries. To achieve these goals, we have synthesized cadmium-free, visible light-emitting QDs using a microwave-assisted continuous flow reactor. After synthesis, the CuInS 2 QD cores underwent a near-complete Zn cation exchange reaction in a batch reactor, followed by the growth of a ZnS shell. Analysis of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy data indicate that the crystal structure changes from CuInS 2 (chalcopyrite) to ZnS (zincblende) during the cation exchange reaction. Compositional analysis indicated that the core/shell QDs were *98 % ZnS, with Cu and In present at much lower concentrations. The photoluminescence (PL) peak position was blue shifted for longer cation exchange reactions, and it was found that the ZnS shell was necessary for improved PL stability.The synthesized QDs have a PL down conversion efficiency of *65 % when using a blue LED source.

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“…Smoothing of the interface in the heteronanocrystals by alloying can enhance the photoluminescence QY significantly due to swift variations in carrier‐confinement potential . As a result, the lattice strain at the interface is reduced significantly, along with a decrease in interfacial defects . The smooth nature of the alloy NC also allows an increase in the charge separation yield as compared with core–shell (type II) NCs with a sharper barrier at the interface.…”

Section: Introductionmentioning

confidence: 99%

An Insight into the Interface through Excited‐State Carrier Dynamics for Promising Enhancement of Power Conversion Efficiency in a Mn‐Doped CdZnSSe Gradient Alloy

Debnath

Parui

Maiti

et al. 2017

Chemistry A European J

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To explore the significance of impurity doping in power conversion efficiency, quaternary gradient CdZnSSe alloy nanocrystals (NCs) and its Mn-doped analogues were synthesized by high-temperature pyrolysis. The undoped and Mn-doped CdZnSSe alloy NCs have been characterized by employing high-resolution TEM, X-ray diffraction, energy-dispersive X-ray spectroscopy, and electron paramagnetic resonance spectroscopy measurements. A low-temperature injection of chalcogens led to a gradient interface in the alloy, comprised of a CdSe/CdS/ZnSe/ZnS nanostructure. Both steady-state and ultrafast time-resolved absorption studies suggested the formation of a charge-transfer (CT) state due to the inner quasi-type II CdSe/CdS part of the gradient CdZnSSe alloy NCs, in which electrons are delocalized throughout the conduction band (CB) of both CdSe and CdS. The CT-state bleach recovery kinetics gave an additional slow electron cooling component (8 ps) in the undoped alloy NCs, which has been assigned to electron equilibration in the delocalized CB before recombination (or trapping). Interestingly, in the presence of dopant Mn, the slow electron cooling component became even more sluggish at 10 ps due to Mn-mediated electron cooling, in which Mn acts as an electron storage center. An unprecedented increase in the photocurrent conversion efficiency (PCE) of approximately 30 % from (3.3±0.11) to (4.29±0.07) % was observed in the Mn-doped gradient alloy compared with the undoped alloy.

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Optical Properties and Exciton Dynamics of Alloyed Core/Shell/Shell Cd_1–xZn_xSe/ZnSe/ZnS Quantum Dots

Cited by 82 publications

References 35 publications

Ultrafast Transient Absorption Studies of Hematite Nanoparticles: The Effect of Particle Shape on Exciton Dynamics

Ultrafast Transient Absorption Studies of Hematite Nanoparticles: The Effect of Particle Shape on Exciton Dynamics

Structural and optical characterization of CuInS2 quantum dots synthesized by microwave-assisted continuous flow methods

An Insight into the Interface through Excited‐State Carrier Dynamics for Promising Enhancement of Power Conversion Efficiency in a Mn‐Doped CdZnSSe Gradient Alloy

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