[Cd5(OH)(H2O)3][CH3CO2]9, a cadmium hydroxy-acetate compound with a layered network

Poul, Laurence; Fakhfakh, M.; Taibi, M.; Jouini, N.; Herson, Patrick; Fiévet, Fernand

doi:10.1007/s10870-005-1439-x

Cited by 10 publications

(11 citation statements)

References 26 publications

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“…Simulations starting from the ‘bridge’ (Figure a) or “chelate” geometries (similar to Figure d) both relaxed to a ‘tilted bridge’ geometry (which is ∼0.25 eV lower in energy), with one of the oxygens bonding to two Cd atoms (Figure b). This geometry is consistent with Cd NMR data for CdSeTe magic-size NCs and single-crystal XRD data for some Cd salts . Previous theoretical studies on smaller Cd 33 Se 33 clusters could not resolve the tilt and reported bridge structure as the most stable one .…”

Section: Resultssupporting

confidence: 88%

“…This geometry is consistent with Cd NMR data for CdSeTe magic-size NCs 43 and single-crystal XRD data for some Cd salts. 51 Previous theoretical studies on smaller Cd 33 Se 33 clusters could not resolve The Journal of Physical Chemistry C ARTICLE the tilt and reported bridge structure as the most stable one. 33 Due to small energy difference, at room temperature the ligand will be continuously switching between the bridge and left-tiltedand right-tilted-bridge configurations.…”

Section: Introductionmentioning

confidence: 99%

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Mobile Surface Traps in CdSe Nanocrystals with Carboxylic Acid Ligands

2011

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Since the discovery of colloidal semiconductor nanocrystals (NCs) they have found tremendous amount of applications in bioimaging, 1 lasing, 2 diodes, 3 single-photon sources, 4 photovoltaics, 5 etc. owing to a wide range of techniques 6 available to tune their optical and electronic properties.Many of those applications rely on emission properties of NCs (quantum yield, emission wavelength broadening and diffusion, Stokes shift, blinking) which are strongly affected by different types of defects, supposedly residing at the surface. 7 Surface traps may also affect the multiexciton generation yields 8 and charge carriers extraction, relevant, e.g., for photovoltaics. Understanding better the source of the trap states can help to develop the synthesis procedures to reduce or ultimately eliminate the traps. In contrast to absorption properties, which are determined mainly by the bulk crystalline structure and the macroscopic properties of the NCs (size, shape), 9,10 surface and thus emission properties require a more detailed knowledge on atomic scale.The exact atomistic nature of surface defects remains unknown 11À13 and the interpretation of experimental data is thus often based on available theoretical models. Several semiempirical studies of ligated surfaces are available 14À18 but this methodology does not reliably capture surface reconstructions and charge redistributions. Few ab initio studies of the NC surfaces available to date addressed only the bare surfaces 19À25 or weakly bound (L-type) ligands. 26À30 However, more and more experimental data suggest that the main type of ligands present on the surface are the covalently bound (X-type) ligands, e.g., deprotonated carboxylic or phosphonic acids. 31À33 Theoretical studies of such ligands on CdSe and PbSe only start to emerge. 30,33À35 In this work we investigate from first principles the atomistic nature of the surface states in NCs. To do this, we choose CdSe NCs without structural defects, small enough to be treated within the density functional theory (DFT) but large enough to distinguish delocalized (core) and localized (trap) states, with carboxylic acid ligands bound covalently. We find that even such an idealized and small model is rich enough to create structures with or without surface trap states, depending on the amount of ligands. Contrary to expectations, apparently more passivated structures (with more ligands and less dangling bonds) exhibit more surface traps. Our most important finding is the presence of mobile surface ligands whose energy levels fluctuate respectively, a feature required by several phenomenological models of blinking. 36À38 We will discuss whether the observed diffusion on its own is capable of explaining the fluorescence intermittency, and whether it is capable of producing switchable longlived trap states. ' COMPUTATIONAL METHODSCalculations were performed within DFT using the SIESTA code. 39 Generalized gradient approximation in a PerdewÀBurkeÀ Ernzerhoff formulation, Troullier-Martins norm-conserving pseudopotenti...

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Section: Resultssupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Mobile Surface Traps in CdSe Nanocrystals with Carboxylic Acid Ligands

2011

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“…The crystal structures of carboxylate salts of Cd frequently show the anions as chelating ligands, so this may be the preferred mode, though some structures show additional coordination of a carboxylate oxygen to a second Cd. [36][37][38][39] Accordingly, this all leads to a model of the probable surface structure of the CdTeSe MSQDs where Cd is attached into the body of the nanocrystal by bonds to two chalcogenides and attached to both oxygen atoms of a carboxylate anion.…”

Section: Resultsmentioning

confidence: 99%

Homogeneously-Alloyed CdTeSe Single-Sized Nanocrystals with Bandgap Photoluminescence

et al. 2009

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Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=16120cb5-f193-4c66-811a-45fa8876ee76 http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=16120cb5-f193-4c66-811a-45fa8876ee76 Homogeneously alloyed ternary CdTeSe magic-sized nanocrystals (MSNs) with bandgap emission were synthesized in 1-octadecene (ODE) via a noninjection one-pot approach featuring synthetic reproducibility and large-scale capability. The noninjection approach used cadmium acetate dihydrate (Cd(OAc) 2 · 2H 2 O), elemental selenium, and elemental tellurium as Cd, Se, and Te sources, respectively. The growth of the CdTeSe nanocrystals was carried out at temperatures from 120 to 200°C for several hours in a reaction flask containing the reactants together with a long-chain fatty acid as capping ligands and ODE as the reaction medium. During synthesis, the CdTeSe nanocrystals exhibited persistent bandgap and did not grow in size anymore after their formation, either with longer growth periods or higher reaction temperature. Also, they exhibit an absorption doublet with 288 meV energy difference between the two peaks; the first excitonic transition peak is at 520 nm and bandgap photoemission peak at 524 nm with full width at half-maximum (fwhm) of ca. 20 nm. Both the growth pattern and the optical properties suggest that they are magic-sized and thus termed as single-sized. Nuclear magnetic resonance (NMR), with sensitivity to local environment, provided valuable information regarding the structure and composition of the nanocrystals. Solid-state 13 C cross polarization/ magic angle spinning (CP/MAS) NMR spectra showed that the carboxylate capping ligand is firmly attached to the crystal, and 1 H decoupled 113 Cd MAS spectra, with and without CP, distinguished between the surface Cd species and the Cd inside a nanocrystal. The 113 Cd NMR results also confirmed, unambiguously, that the nanocrystals are homogeneously alloyed ternary CdTeSe, with 113 C...

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“…Crystalline materials are obtained in ethylene glycol and the structural resolutions clearly showed that the monoanion state of the polyol complex with the metal cations to form glycoxide species. 74,75 To test the hypothesis, initially, the synthesis of cobalt metal particles using cobalt chloride in ethylene glycol was attempted. Though cobalt chloride dissolved in ethylene glycol, the solution changed its color from pink (at RT) to blue and no visible precipitate was obtained even when the solution was heated to the boiling point of ethylene glycol and refluxed at this temperature for more than 24 hours.…”

Section: Experimental Verification Of Theoretical Predictionsmentioning

confidence: 99%