Demonstration of a shell-core structure in layered cadmium selenide-zinc selenide small particles by x-ray photoelectron and Auger spectroscopies

Hoener, Carolyn F.; Allan, K.; Bard, Allen J.; Campion, Alan; Fox, Marye Anne; Mallouk, Thomas E.; Webber, S. E.; White, J. M.

doi:10.1021/j100188a045

Cited by 236 publications

(168 citation statements)

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“…XPS is normally considered to be a surface sensitive technique, with a typical penetration depth of up to 10 nm. 38 However, in this case, as our QDs are around 3 nm in diameter, this technique probes the whole QD volume. The reference pure InP QD sample (black spectrum in figure 2a) shows a In 3d 5 The agreement between XPS and ICP-OES results therefore strongly supports the formation of an In x Zn y P alloy structure.…”

Section: Resultsmentioning

confidence: 99%

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

et al. 2016

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Colloidal quantum dots (QDs) show great promises as LED phosphors due to their tuneable narrow-band emission and ability to produce high-quality white light.Currently, the most suitable QDs for lighting applications are based on cadmium, which presents a toxicity problem for consumer applications. The most promising cadmiumfree candidate QDs are based on InP, but their quality lags much behind that of cadmium based QDs. This is not only because the synthesis of InP QDs is more challenging than that of Cd-based QDs, but also because the large lattice parameter of InP makes it difficult to grow an epitaxial, defect free shell on top of such material. Here we propose an original approach to overcome this problem by alloying InP nanocrystals with Zn 2+ ions, which enables the synthesis of In x Zn y P alloy QDs having lattice constant that can be tuned from 5.93 Å (pure InP QDs) down to 5.39 Å by simply varying the concentration of the Zn precursor. This lattice engineering allows for subsequent strainfree, epitaxial growth of a ZnSe z S 1-z shell with lattice parameters matching that of the core. We demonstrate, for a wide range of core and shell compositions (i.e. varying x, y and z), that the photoluminescence quantum yield is maximal (up to 60%) when lattice mismatch is minimal.3

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Section: Resultsmentioning

confidence: 99%

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

et al. 2016

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“…core nanocrystals with a higher band-gap (CdS, ZnSe, ZnS…) shells is an attractive possibility that leads to the core/shell QDs with improved luminescence, higher stability (protected from the surrounding environment), and perfect electrically connection (Korton et al, 1990, Hoener et al, 1992, Hines & Guyot-Sionnest, 1996. In early 90 th the CdSe nanocrystals have been successfully capped with ZnS (Kortan et al, 1990;Hines et al, 1996) and ZnSe (Hoener et al, 1992) for modification the surface passivation conditions. An advantage of ZnS shell in comparison with CdS shell is that ZnS forms at lower temperatures than CdS and ZnS and CdSe do not alloy well.…”

Section: Optical Properties Of Ii-vi Semiconductor Core/shell Qdsmentioning

confidence: 99%

Semiconductor II-VI Quantum Dots with Interface States and Their Biomedical Applications

Torchynska¹,

Vorobiev²

2011

Advanced Biomedical Engineering

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“…123 Therefore, ZnS and CdS are often used to shell CdSe and CdTe quantum dots. 124 The photophysical properties of quantum dots are dictated by their size. As described, an absorbed photon in a bulk material creates a bound electron-hole pair that can easily maintain a spatial separation equal to the exciton Bohr radius.…”

Section: Quantum Dot Structure and Optical Propertiesmentioning

confidence: 99%

Photophysics of Individual Single-Walled Carbon Nanotubes

2008

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Single-walled carbon nanotubes (SWNTs) are cylindrical graphitic molecules that have remained at the forefront of nanomaterials research since 1991, largely due to their exceptional and unusual mechanical, electrical, and optical properties. The motivation for understanding how nanotubes interact with light (i.e., SWNT photophysics) is both fundamental and applied. Individual nanotubes may someday be used as superior near-infrared fluorophores, biological tags and sensors, and components for ultrahigh-speed optical communications systems. Establishing an understanding of basic nanotube photophysics is intrinsically significant and should enable the rapid development of such innovations. Unlike conventional molecules, carbon nanotubes are synthesized as heterogeneous samples, composed of molecules with different diameters, chiralities, and lengths. Because a nanotube can be either metallic or semiconducting depending on its particular molecular structure, SWNT samples are also mixtures of conductors and semiconductors. Early progress in understanding the optical characteristics of SWNTs was limited because nanotubes aggregate when synthesized, causing a mixing of the energy states of different nanotube structures. Recently, significant improvements in sample preparation have made it possible to isolate individual nanotubes, enabling many advances in characterizing their optical properties. In this Account, single-molecule confocal microscopy and spectroscopy were implemented to study the fluorescence from individual nanotubes. Single-molecule measurements naturally circumvent the difficulties associated with SWNT sample inhomogeneities. Intrinsic SWNT photoluminescence has a simple narrow Lorentzian line shape and a polarization dependence, as expected for a one-dimensional system. Although the local environment heavily influences the optical transition wavelength and intensity, single nanotubes are exceptionally photostable. In fact, they have the unique characteristic that their single molecule fluorescence intensity remains constant over time; SWNTs do not “blink” or photobleach under ambient conditions. In addition, transient absorption spectroscopy was used to examine the relaxation dynamics of photoexcited nanotubes and to elucidate the nature of the SWNT excited state. For metallic SWNTs, very fast initial recovery times (300–500 fs) corresponded to excited-state relaxation. For semiconducting SWNTs, an additional slower decay component was observed (50–100 ps) that corresponded to electron–hole recombination. As the excitation intensity was increased, multiple electron–hole pairs were generated in the SWNT; however, these e−h pairs annihilated each other completely in under 3 ps. Studying the dynamics of this annihilation process revealed the lifetimes for one, two, and three e−h pairs, which further confirmed that the photoexcitation of SWNTs produces not free electrons but rather one-dimensional bound electron–hole pairs (i.e., excitons). In summary, nanotube photophysics is a rapidly developing area o...

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Demonstration of a shell-core structure in layered cadmium selenide-zinc selenide small particles by x-ray photoelectron and Auger spectroscopies

Cited by 236 publications

References 0 publications

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Semiconductor II-VI Quantum Dots with Interface States and Their Biomedical Applications

Photophysics of Individual Single-Walled Carbon Nanotubes

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Demonstration of a shell-core structure in layered cadmium selenide-zinc selenide small particles by x-ray photoelectron and Auger spectroscopies

Cited by 236 publications

References 0 publications

Tuning the Lattice Parameter of InxZnyP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Tuning the Lattice Parameter of InxZnyP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Semiconductor II-VI Quantum Dots with Interface States and Their Biomedical Applications

Photophysics of Individual Single-Walled Carbon Nanotubes

Contact Info

Product

Resources

About

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

Tuning the Lattice Parameter of In_xZn_yP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots