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61.
Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with Tunable Composition and Thickness by Ultrasonication
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Yu Tong Eva Bladt Meltem F. Aygüler Aurora Manzi Dr. Karolina Z. Milowska Verena A. Hintermayr Prof. Dr. Pablo Docampo Prof. Dr. Sara Bals Dr. Alexander S. Urban Dr. Lakshminarayana Polavarapu Prof. Dr. Jochen Feldmann 《Angewandte Chemie (International ed. in English)》2016,55(44):13887-13892
We describe the simple, scalable, single‐step, and polar‐solvent‐free synthesis of high‐quality colloidal CsPbX3 (X=Cl, Br, and I) perovskite nanocrystals (NCs) with tunable halide ion composition and thickness by direct ultrasonication of the corresponding precursor solutions in the presence of organic capping molecules. High angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) revealed the cubic crystal structure and surface termination of the NCs with atomic resolution. The NCs exhibit high photoluminescence quantum yields, narrow emission line widths, and considerable air stability. Furthermore, we investigated the quantum size effects in CsPbBr3 and CsPbI3 nanoplatelets by tuning their thickness down to only three to six monolayers. The high quality of the prepared NCs (CsPbBr3) was confirmed by amplified spontaneous emission with low thresholds. The versatility of this synthesis approach was demonstrated by synthesizing different perovskite NCs. 相似文献
62.
The major arsenosugar compounds have been reported to be hydride-generation-active, however to a lesser extent in comparison
with the inorganic arsenicals. We report here for the first time the identity and quantity of the volatile arsenicals generated
by As-sugar-SO3, As-sugar-SO4, dimethylarsinoyl acetic acid and dimethylarsinoyl ethanol. Only one major volatile compound was identified for all four
compounds studied: dimethylarsine. This means that the As–C bond to the longer carbon chain was cleaved during the hydride-generation
process. Theoretical calculations at the RHF/6-31G(d,p) ab initio level confirm that this As–C bond is much weaker than the
As–CH3 bonds. Furthermore, it was revealed that the sulphur analogue of dimethylarsinic acid (DMAS ) is hydride-generation-active
at pH 7 in contrast to dimethylarsinic acid, despite the fact that arsenic is also pentavalent. This has been substantiated
by the calculation of the change in susceptibility of the arsenic towards nucleophilic attack when oxygen is replaced by sulphur.
Hence, DMAS can easily be mistaken for a trivalent arsenic species. 相似文献
63.
H. Feldmann R. Oppermann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):429-445
We analyse the competition between spin glass (SG) order and local pairing superconductivity (SC) in the fermionic Ising spin
glass with frustrated fermionic spin interaction and nonrandom attractive interaction. The phase diagram is presented for
all temperatures T and chemical potentials μ. SC-SG transitions are derived for the relevant ratios between attractive and frustrated-magnetic
interaction. Characteristic features of pairbreaking caused by random magnetic interaction and/or by spin glass proximity
are found. The existence of low-energy excitations, arising from replica permutation symmetry breaking (RPSB) in the Quantum
Parisi Phase, is shown to be relevant for the SC-SG phase boundary. Complete 1-step RPSB-calculations for the SG-phase are
presented together with a few results for -step breaking. Suppression of reentrant SG-SC-SG transitions due to RPSB is found and discussed in context of ferromagnet-SG
boundaries. The relative positioning of the SC and SG phases presents a theoretical landmark for comparison with experiments
in heavy fermion systems and high superconductors. We find a crossover line traversing the SG-phase with as its quantum critical (end)point in complete RPSB, and scaling is proposed for its vicinity. We argue that this line indicates
a random field instability and suggest Dotsenko-Mézard vector replica symmetry breaking to occur at low temperatures beyond.
Received 26 November 1998 and Received in final form 25
January 1999 相似文献
64.
We investigate non-equilibrium relaxation processes in optically excited large gold and silver clusters. Time-resolved pump-probe
experiments and model calculations show that optical excitation of the clusters by femtosecond laser pulses results in a heating
of the electron system, which is followed by electron cooling via phonon emission. The electron heating leads to an enhanced
damping of the surface-plasmon resonance in the clusters. This enhanced damping is caused by an enhancement of the Landau
damping and electron scattering rates at high electron temperatures. Furthermore, we find that the rate of electron cooling
in the clusters changes with electron temperature; this is a consequence of the temperature-dependent specific heat of the
conduction electrons. Finally, pump-probe experiments on ellipsoidal silver clusters show that the thermal expansion of the
heated clusters triggers mechanical vibrations at the acoustic eigenfrequencies of the clusters.
Received: 6 December 1999 / Published online: 7 August 2000 相似文献
65.
I. Koch J. Feldmann J. Lintschinger S. V. Serves W. R. Cullen K. J. Reimer 《应用有机金属化学》1998,12(2):129-136
The method of hydride generation for the speciation of antimony compounds was examined with respect to the problem of molecular "rearrangement'. Specifically, demethylation of trimethylstilbine during the analysis of trimethylantimony dichloride (Me3SbCl2) was studied. Previously published observations that enhanced demethylation takes place as a result of inadequate preconditioning of the analytical apparatus were found to be not reproducible. However, demethylation was enhanced as the pH decreased when using two different analytical methods: semi-continuous flow hydride generation–gas chromatography–atomic absorption spectrometry (HG– GC–AAS), and batch-type hydride generation– gas chromatography–inductively coupled plasma mass spectrometry (HG–GC–ICP MS). Applications of the hydride generation method to environmental samples revealed differences in analytical results at high and low pH, and enhanced demethylation taking place because of the matrix in a fungal extract sample. The authors recommend that researchers using the method of hydride generation for antimony compounds carefully test the reaction conditions with standard compounds and use the method of standard addition only. © 1998 John Wiley & Sons, Ltd. 相似文献
66.
By reaction of GeI4, [N(nBu)4]I as iodide donor, and [NMe(nBu)3][N(Tf)2] as ionic liquid, reddish‐black, plate‐like shaped crystals are obtained. X‐ray diffraction analysis of single crystals resulted in the compositions ;alpha;‐[NMe(nBu)3](GeI4)I (Pbca; a = 1495.4(3) pm; b = 1940.6(4) pm; c = 3643.2(7) pm; Z = 16) and β‐[NMe(nBu)3](GeI4)I (Pn; a = 1141.5(2) pm; b = 953.6(2) pm; c = 1208.9(2) pm; β = 100.8(1)°; Z = 2). Depending on the reaction temperature, the one or other compound is formed selectively. In addition, the reaction of GeI4 and [N(nBu)4]I, using [ImMe(nBu)][BF4] (Im = imidazole) as ionic liquid, resulted in the crystallization of [ImMe(nBu)][N(nBu)4](GeI4)3I2 (P21/c; a = 1641.2(3) pm; b = 1903.0(4) pm; c = 1867.7(4) pm; β = 92.0(1)°; Z = 4). The anionic network of all three compounds is established by molecular germanium(IV)iodide, which is bridged by iodide anions. The different connectivity of (GeI4–I–) networks is attributed to the flexibility of I– regarding its coordination and bond length. Here, a [3+1]‐, 4‐ and 5‐fold coordination is first observed in the pseudo‐ternary system M/Ge/I (M: cation). 相似文献
67.
The instability of metal and metalloid complexes during analytical processes has always been an issue of an uncertainty regarding
their speciation in plant extracts. Two different speciation protocols were compared regarding the analysis of arsenic phytochelatin
(AsIIIPC) complexes in fresh plant material. As the final step for separation/detection both methods used RP-HPLC simultaneously
coupled to ICP-MS and ES-MS. However, one method was the often used off-line approach using two-dimensional separation, i.e.
a pre-cleaning step using size-exclusion chromatography with subsequent fraction collection and freeze-drying prior to the
analysis using RP-HPLC–ICP-MS and/or ES-MS. This approach revealed that less than 2% of the total arsenic was bound to peptides
such as phytochelatins in the root extract of an arsenate exposed Thunbergia alata, whereas the direct on-line method showed that 83% of arsenic was bound to peptides, mainly as AsIIIPC3 and (GS)AsIIIPC2. Key analytical factors were identified which destabilise the AsIIIPCs. The low pH of the mobile phase (0.1% formic acid) using RP-HPLC–ICP-MS/ES-MS stabilises the arsenic peptide complexes
in the plant extract as well as the free peptide concentration, as shown by the kinetic disintegration study of the model
compound AsIII(GS)3 at pH 2.2 and 3.8. But only short half-lives of only a few hours were determined for the arsenic glutathione complex. Although
AsIIIPC3 showed a ten times higher half-life (23 h) in a plant extract, the pre-cleaning step with subsequent fractionation in a mobile
phase of pH 5.6 contributes to the destabilisation of the arsenic peptides in the off-line method. Furthermore, it was found
that during a freeze-drying process more than 90% of an AsIIIPC3 complex and smaller free peptides such as PC2 and PC3 can be lost. Although the two-dimensional off-line method has been used successfully for other metal complexes, it is concluded
here that the fractionation and the subsequent freeze-drying were responsible for the loss of arsenic phytochelatin complexes
during the analysis. Hence, the on-line HPLC–ICP-MS/ES-MS is the preferred method for such unstable peptide complexes. Since
freeze-drying has been found to be undesirable for sample storage other methods for sample handling needed to be investigated.
Hence, the storage of the fresh plant at low temperature was tested. We can report for the first time a storage method which
successfully conserves the integrity of the labile arsenic phytochelatin complexes: quantitative recovery of AsIIIPC3 in a formic acid extract of a Thunbergia alata exposed for 24 h to 1 mg Asv L−1 was found when the fresh plant was stored for 21 days at 193 K.
Figure On-line HPLC–ICP-MS/ES-MS (bottom) is the preferred method for MS determination of unstable arsenic peptide complexes in plant extracts, since this avoids
fractionation and subsequent freeze-drying that are responsible for loss of arsenic phytochelatin complexes in the 2D off-line
method (top)
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
68.
Becker K Lupton JM Feldmann J Setayesh S Grimsdale AC Müllen K 《Journal of the American Chemical Society》2006,128(3):680-681
Intramolecular energy transfer is investigated in an endcapped conjugated polymer on the single molecule level at low temperature. While light harvesting in one dimension is on average inefficient in the ensemble, the efficiency scatters widely on the single molecule level, with some molecules exhibiting near-unity transfer probability from the polymer backbone donor to the acceptor endcap. This transfer occurs in the absence of spectral overlap between donor and acceptor, as the electronic and vibronic transitions narrow substantially at low temperatures once inhomogeneous disorder broadening is overcome. The results illustrate how far-field absorption and emission characteristics of molecular transitions are insufficient to describe resonant energy transfer processes following F?rster theory in multichromophoric aggregates. Rather, exciton trapping due to efficient multiphonon emission has to be invoked with a possible contribution of strong polaronic coupling. 相似文献
69.
Kriegel I Jiang C Rodríguez-Fernández J Schaller RD Talapin DV da Como E Feldmann J 《Journal of the American Chemical Society》2012,134(3):1583-1590
The optical properties of stoichiometric copper chalcogenide nanocrystals (NCs) are characterized by strong interband transitions in the blue part of the spectral range and a weaker absorption onset up to ~1000 nm, with negligible absorption in the near-infrared (NIR). Oxygen exposure leads to a gradual transformation of stoichiometric copper chalcogenide NCs (namely, Cu(2-x)S and Cu(2-x)Se, x = 0) into their nonstoichiometric counterparts (Cu(2-x)S and Cu(2-x)Se, x > 0), entailing the appearance and evolution of an intense localized surface plasmon (LSP) band in the NIR. We also show that well-defined copper telluride NCs (Cu(2-x)Te, x > 0) display a NIR LSP, in analogy to nonstoichiometric copper sulfide and selenide NCs. The LSP band in copper chalcogenide NCs can be tuned by actively controlling their degree of copper deficiency via oxidation and reduction experiments. We show that this controlled LSP tuning affects the excitonic transitions in the NCs, resulting in photoluminescence (PL) quenching upon oxidation and PL recovery upon subsequent reduction. Time-resolved PL spectroscopy reveals a decrease in exciton lifetime correlated to the PL quenching upon LSP evolution. Finally, we report on the dynamics of LSPs in nonstoichiometric copper chalcogenide NCs. Through pump-probe experiments, we determined the time constants for carrier-phonon scattering involved in LSP cooling. Our results demonstrate that copper chalcogenide NCs offer the unique property of holding excitons and highly tunable LSPs on demand, and hence they are envisaged as a unique platform for the evaluation of exciton/LSP interactions. 相似文献
70.
Claus Feldmann Dominic Freudenmann 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(10):i68-i70
The title compound, [Te8][NbOCl4]2, was obtained as translucent black crystals by reaction of elemental tellurium, niobium(V) chloride and niobium(V) oxychloride in the ionic liquid BMImCl (BMImCl is 1‐butyl‐3‐methylimidazolium chloride). The synthesis was performed in argon‐filled glass ampoules. According to X‐ray structure analysis based on single crystals, the title compound crystallizes with triclinic lattice symmetry and consists of infinite {[Te8]2+}n cations associated with pyramidal [NbOCl4]− anions. The novel catena‐octatellurium(2+) cation is composed of Te5 rings that are linked via Te3 units [Te—Te = 2.6455 (18)–2.8164 (19) Å]. The composition and purity of [Te8][NbOCl4]2 were further confirmed by energy‐dispersive X‐ray diffraction (EDX) analysis. 相似文献