The Magic-Size Nanocluster (CdSe)<sub>34</sub> as a Low-Temperature Nucleant for Cadmium Selenide Nanocrystals; Room-Temperature Growth of Crystalline Quantum Platelets

Wang, Yuanyuan; Zhang, Ying; Wang, Fudong; Giblin, Daryl; Hoy, Jessica; Rohrs, Henry W.; Loomis, Richard A.; Buhro, William E.

doi:10.1021/cm404068e

Cited by 131 publications

(262 citation statements)

References 42 publications

(147 reference statements)

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“…61,[125][126][127] The cadmium precursor dissolved in amines forms anisotropically ordered layers which will serve as templates for the nucleation and growth of the wurtzite nanoplates once the precursors of selenium is introduced. Both Hyeon 128 and Buhro's groups 118 have spectroscopically observed at the early stage of the synthesis the formation of magic sized clusters with a majority of More recently, Buhro and co-workers 124 have also shown that instead of using a pure primary amine, a mixture of a primary and secondary amine to dissolve the cadmium precursor allows the formation of CdSe quantum platelets with pure (CdSe)34 magic sized cluster as intermediate of the reaction at room temperature. The (CdSe)34 clusters can also convert to the more thermodynamically stable (CdSe)13 by lowering the temperature to 0°C, but then the annealing temperature should be higher to crystallize them in quantum platelets.…”

Section: Ligand Templatingmentioning

confidence: 99%

Two-Dimensional Colloidal Nanocrystals

et al. 2016

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Abstract:In this paper, we review recent progresses on colloidal growth of 2D nanocrystals.We identify four main sources of anisotropy which lead to the formation of plate-and sheetlike colloidal nanomaterials. Defect induced anisotropy is a growth method which relies on the presence of topological defects at the nanoscale to induce 2D shapes objects. Such a method is particularly important in the growth of metallic nanoobjects. Another way to induce anisotropy is based on ligand engineering. The availability of some nanocrystal facets can be tuned by selectively covering the surface with ligands of tunable thickness. Cadmium chalcogenides nanoplatelets (NPLs) strongly rely on this method which offers atomic control in the thinner direction, down to a few monolayers. 2D objects can also be obtained by post or in situ self-assembly of nanocrystals. This growth method differs from the previous ones in the sense that the elementary objects are not molecular precursors, and is a common method for lead chalcogenide compounds. Finally, anisotropy may simply rely on the lattice anisotropy itself as it is common for rod-like nanocrystals. Colloidally grown Transition Metal DiChalcogenides (TMDC) in particular result from such process. We also present hybrid syntheses which combine several of the previously described methods and other paths, such as cation exchange, which expand the range of available materials. Finally, we discuss in which sense 2D-objects differ from 0D nanocrystals and review some of their applications in optoelectronics, including lasing and photodetection, and biology.

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Section: Ligand Templatingmentioning

confidence: 99%

Two-Dimensional Colloidal Nanocrystals

et al. 2016

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“…[20][21][22][23][24] A narrow size distribution would result in a sharp band-edge PL peak rather than a combination of band-edge and broadband peaks. The broad PL feature and short PL lifetimes suggest the presence of surface related trap sites in the PNCs, not their size distribution.…”

Section: Scheme 1 Schematic Presentation Of the Synthesis Of White-lmentioning

confidence: 99%

Pure white-light emitting ultrasmall organic–inorganic hybrid perovskite nanoclusters

et al. 2016

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Organic-inorganic hybrid perovskites, direct band-gap semiconductors have shown tremendous promise for optoelectronic device fabrication. We report the first colloidal synthetic approach to prepare ultrasmall (~1.5 nm diameter), white light emitting, organic-inorganic hybrid perovskite nanoclusters. The nearly pure white-light emitting ultrasmall nanoclusters were obtained by selectively manipulating the surface chemistry (passivating ligands and surface trap-states) and controlled substitution of halide ions. The nanoclusters displayed a combination of band-edge and broadband photoluminescence properties, covering a major part of the visible region of the solar spectrum with unprecedentedly large quantum yields of ~12% and photoluninescence lifetime of ~20 ns. The intrinsic white light emission of perovskite nanoclusters makes them ideal and low cost hybrid nanomaterials for solid-state lighting applications.The ever-increasing global demand for energy drives the need to discover highly efficient materials capable of saving energy in solid-state lighting (SSL) applications, such as light-emitting diodes (LEDs). 1,2 In this context, pure white-light emitting materials, and their subsequent uses in LED fabrication, will be a most effective way to reduce global power consumption. Currently, white-light LEDs are prepared by: (i) mixing single wavelength emitting organic phosphors, 3 and (ii) constructing multi-layer films composed of blue, green, and red color emitting semiconductor quantum dots (QDs). 4,5 However, the self-absorption process between different organic phosphors reduces device efficiency, a similar device characteristic that has also been observed for QD-based LEDs. Ultrasmall semiconductor nanoclusters (e.g., CdSe) display white-light, but they require expensive, complicated and high temperature synthetic methods. [6][7][8] Recently, white-light emitting bulk organic-inorganic perovskites were synthesized, 9,10 which would not only expand SSL research but also facilitate inexpensive LED fabrication. Scheme 1. Schematic Presentation of the Synthesis of White-Light Emitting Organolead Bromide Perovskite NanoclustersIn this communication, we report the first colloidal synthetic method to prepare white-light emitting, ultrasmall (~1.5 nm diameter) methylammonium lead bromide (MAPbBr3) perovskite nanoclusters (PNCs). Their synthesis is outlined in Scheme 1 and the detailed procedure is provided in the Electronic Supplementary Information (ESI) file. These PNCs display a combination of band-edge and broadband photoluminescence (PL) with a quantum yield (QY) of ~5% and PL lifetime of ~7 ns. We hypothesize that the broad emission properties originate from the presence of surface-related midgap trap-states. Furthermore, we showed selective manipulation of band-gap and trap-states via the preparation of mixed halide (MAPbClxBr3-x) PNCs through controlled anion exchange reactions enhanced both QY and PL lifetime at least two-fold. We believe these ultrasmall PNCs will provide fundamentally important informati...

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“…Very recently, low temperature, nonphosphinated methods for synthesis of ultrasmall CdSe nanocrystals were reported. [30][31] In order to address the current challenges of understanding the formation mechanism of semiconductor nanocrystals, we have investigated here the formation of ~1.6 nm CdSe nanocrystals using a new Se precursor (Scheme 1) prepared from a reaction between elemental selenium and 1-octadecene (ODE) requiring 1-hexanethiol (HT), which will be heretofore referred to as Se-ODE-HT. From 77 Se and 1 H NMR, and MS characterizations, we identify this Se-ODE-HT precursor as a new Se-bridged organic species that can be used in CdSe nanocrystals synthesis as the reactive Se precursor.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

Dolai¹,

Dutta

Muhoberac³

et al. 2015

Chem. Mater.

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ABSTRACT:We have designed a new non-phosphinated reaction pathway, which includes synthesis of a new, highly reactive Se-bridged organic species (chalcogenide precursor), to produce bright white light-emitting ultrasmall CdSe nanocrystals of high quality under mild reaction conditions. The detailed characterization of structural properties of the selenium precursor through combined 77 Se NMR and laser desorption ionization-mass spectrometry (LDI-MS) provided valuable insights into Se release and delineated the nanocrystal formation mechanism at the molecular level. The 1 H NMR study showed that the rate of disappearance of Se-precursor maintained a single-exponential decay with a rate constant of 2.3 x 10 -4 s -1 at room temperature. Furthermore, the combination of LDI-MS and optical spectroscopy was used for the first time to deconvolute the formation mechanism of our bright white light-emitting nanocrystals, which demonstrated initial formation of a smaller key nanocrystal intermediate (CdSe)19. Application of thermal driving force for destabilization resulted in (CdSe)n nanocrystal generation with n = 29-36 through continuous dissolution and addition of monomer onto existing nanocrystals while maintaining a living-polymerization type growth mode. Importantly, our ultrasmall CdSe nanocrystals displayed an unprecedentedly large fluorescence quantum yield of ~27% for this size regime (<2.0 nm diameter). These mixed oleylamine and cadmium benzoate ligand-coated CdSe nanocrystals showed a fluorescence lifetime of ~90 ns, a significantly large value for such small nanocrystals, which was due to delocalization of the exciton wavefunction into the ligand monolayer. We believe our findings will be relevant to formation of other metal chalcogenide nanocrystals through expansion of the understanding and manipulation of surface ligand chemistry, which together will allow the preparation of "artificial solids" with high charge conductivity and mobility for advanced solid-state device applications.3

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The Magic-Size Nanocluster (CdSe)₃₄ as a Low-Temperature Nucleant for Cadmium Selenide Nanocrystals; Room-Temperature Growth of Crystalline Quantum Platelets

Cited by 131 publications

References 42 publications

Two-Dimensional Colloidal Nanocrystals

Two-Dimensional Colloidal Nanocrystals

Pure white-light emitting ultrasmall organic–inorganic hybrid perovskite nanoclusters

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

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The Magic-Size Nanocluster (CdSe)34 as a Low-Temperature Nucleant for Cadmium Selenide Nanocrystals; Room-Temperature Growth of Crystalline Quantum Platelets

Cited by 131 publications

References 42 publications

Two-Dimensional Colloidal Nanocrystals

Two-Dimensional Colloidal Nanocrystals

Pure white-light emitting ultrasmall organic–inorganic hybrid perovskite nanoclusters

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

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The Magic-Size Nanocluster (CdSe)₃₄ as a Low-Temperature Nucleant for Cadmium Selenide Nanocrystals; Room-Temperature Growth of Crystalline Quantum Platelets