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Journal ArticleDOI: 10.1039/D1TA00428J

Revisiting the nanocrystal formation process of zero-dimensional perovskite

02 Mar 2021-Journal of Materials Chemistry (Royal Society of Chemistry (RSC))-Vol. 9, Iss: 8, pp 4658-4663
Abstract: The nanocrystal (NC) form of zero-dimensional perovskite (Cs4PbBr6) has attracted a great deal of attention due to both its elusive green emission and phase-pure nature, which has posed a major challenge to the impurity theory used to explain CsPbBr3 being an emitter In this work, we revisit the NC formation process in real time by using an in situ photoluminescence (PL) monitoring system Through analyzing the evolution of the PL spectra, the formation process was divided into two stages, namely the nucleation stage and growing stage, which were well explained by the LaMer mechanism and the Ostwald ripening model In addition, the Johnson–Mehl–Avrami (JMA) model was used to simulate the transformation from non-emissive Cs4PbBr6 to green-emitting Cs4PbBr6, and the ensuing activation energy (Ea = 390 ± 50 kJ mol−1) was extracted Importantly, an accompanied transformation from “white spots” to “black spots” was observed, which suggested that the black spots were responsible for PL emission despite their amorphous nature Our work represents a step forward in unraveling the PL origin of the Cs4PbBr6 phase, although the nature of the white and black spots remained elusive

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Topics: Black spot (54%)

5 results found

Journal ArticleDOI: 10.1039/D1TC02571F
Abstract: Ligand-free Cs4PbBr6 particles of sub-micron dimensions were fabricated by a simple tip-sonication method showing 85.1% photoluminescence quantum yield (PLQY). Cs4PbBr6 microcrystals can be grown under saturated vapor pressure with the particles as nucleation units. Surface traps are the main defects in the Cs4PbBr6 particles with smaller size, whereas bulk defects dominate in the larger microcrystals. The intensity of the low energy PL peak increases with excitation intensity at low temperature, which can be assigned to band filling and charge transfer effects. The exciton binding energy of Cs4PbBr6 particles is 180 meV which is almost twice that of the Cs4PbBr6 microcrystals. Such tight binding of the excitons facilitates exciton radiative recombination. In addition, the long excited-state lifetime of the Cs4PbBr6 particles contributes to the higher PLQY compared to that of comparable microcrystals. Time-resolved emission microscopy images clearly indicate different recombination kinetics in the ordered and defect regions, which is hidden in ensemble measurements. This strongly suggests that surface trap states are the main reason for the high-efficiency photoluminescence of the intrinsic Cs4PbBr6 particles investigated here, although both surface and bulk traps can emit light.

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Topics: Photoluminescence (54%), Exciton (52%)

Journal ArticleDOI: 10.1016/J.PHYSE.2021.115038
Abstract: Quantum confinement effect can be realized by decreasing the structural dimension of perovskites . Although zero-dimensional perovskites (Cs 4PbBr6) demonstrate high fluorescence efficiency, it is still controversy about the nature of green emission and carrier recombination dynamics. In this work, phase-pure Cs4PbBr6 powder has been prepared in aqueous solution which supplies enough CsBr during the reaction. The high photoluminescence quantum yield (56.4%) of Cs 4PbBr6 is ascribed to high exciton binding energy 172 meV, which likely confines the excitons in the separated octahedral unit and facilitates exciton radiative recombination. The carrier recombination process is mainly trap states mediated recombination rather than bimolecular recombination which dominates in CsPbBr 3 thin films/nanocrystals. Spatially and temporally resolved fluorescence measurement clearly shows the whole regions of Cs4PbBr6 are fluorescent. These observations confirm that the green emission of Cs4PbBr6 originates from the trap states rather than the CsPbBr3 impurities, which is beneficial to its application in the field of optoelectronic devices .

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Topics: Photoluminescence (55%), Exciton (52%), Potential well (52%) ... show more


41 results found

Journal ArticleDOI: 10.1021/JA906506J
Abstract: Although gold nanoparticles (GNP) are among the most intensely studied nanoscale materials, the actual mechanisms of GNP formation often remain unclear due to limited accessibility to in situ-derived time-resolved information about precursor conversion and particle size distribution Overcoming such limitations, a method is presented that analyzes the formation of nanoparticles via in situ SAXS and XANES using synchrotron radiation The method is applied to study the classical GNP synthesis route via the reduction of tetrachloroauric acid by trisodium citrate at different temperatures and reactant concentrations A mechanism of nanoparticle formation is proposed comprising different steps of particle growth via both coalescence of nuclei and further monomer attachment The coalescence behavior of small nuclei was identified as one essential factor in obtaining a narrow size distribution of formed particles

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Topics: Nanoparticle (52%), Coalescence (physics) (52%), Trisodium citrate (51%) ... show more

527 Citations

Journal ArticleDOI: 10.1016/0040-6031(95)02466-2
01 Dec 1995-Thermochimica Acta
Abstract: The Johnson-Mehl-Avrami equation is frequently used for analysis of experimental data of non-isothermal crystallization kinetics although this theoretical model has limited applicability for the non-isothermal transformations involving nucleation and growth. It is shown that the applicability of this model should be tested by reliable methods before a quantitative analysis of non-isothermal crystallization data is made. Such testing methods are described and their uses are demonstrated.

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Topics: Crystallization (56%), Nucleation (53%), Thermal analysis (51%)

363 Citations

Journal ArticleDOI: 10.1007/BF01105093
Eric J. Mittemeijer1Institutions (1)
Abstract: A common basis of reaction-rate theories is discussed for isothermal and non-isothermal transformations As a result compatible recipes have been obtained for the extraction of kinetic parameters from isothermally and non-isothermally conducted experiments It follows that so-called Kissinger-like methods for non-isothermal kinetic analysis, originally derived for homogeneous reactions, can also be applied to heterogeneous reactions, and that these methods constitute (only) a special case of the general analysis proposed The recipes presented are illustrated by a series of examples taken from recent research on solid-state transformations; among other things, isothermal and non-isothermal analyses of the same transformation are compared and use of the notion of “effective activation energy”, that varies during the course of an overall transformation, is discussed

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358 Citations

Open accessJournal ArticleDOI: 10.1021/ACS.NANOLETT.6B05262
20 Feb 2017-Nano Letters
Abstract: We have developed a colloidal synthesis of nearly monodisperse nanocrystals of pure Cs4PbX6 (X = Cl, Br, I) and their mixed halide compositions with sizes ranging from 9 to 37 nm. The optical absorption spectra of these nanocrystals display a sharp, high energy peak due to transitions between states localized in individual PbX64– octahedra. These spectral features are insensitive to the size of the particles and in agreement with the features of the corresponding bulk materials. Samples with mixed halide composition exhibit absorption bands that are intermediate in spectral position between those of the pure halide compounds. Furthermore, the absorption bands of intermediate compositions broaden due to the different possible combinations of halide coordination around the Pb2+ ions. Both observations are supportive of the fact that the [PbX6]4– octahedra are electronically decoupled in these systems. Because of the large band gap of Cs4PbX6 (>3.2 eV), no excitonic emission in the visible range was observed...

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Topics: Halide (54%), Band gap (51%), Absorption (chemistry) (51%)

343 Citations

Journal ArticleDOI: 10.1021/NN901499C
20 Jan 2010-ACS Nano
Abstract: Gold nanoparticles (AuNP) were prepared by the homogeneous mixing of continuous flows of an aqueous tetrachloroauric acid solution and a sodium borohydride solution applying a microstructured static mixer. The online characterization and screening of this fast process (∼2 s) was enabled by coupling a micromixer operating in continuous-flow mode with a conventional in-house small angle X-ray scattering (SAXS) setup. This online characterization technique enables the time-resolved investigation of the growth process of the nanoparticles from an average radius of ca. 0.8 nm to about 2 nm. To the best of our knowledge, this is the first demonstration of a continuous-flow SAXS setup for time-resolved studies of nanoparticle formation mechanisms that does not require the use of synchrotron facilities. In combination with X-ray absorption near edge structure microscopy, scanning electron microscopy, and UV−vis spectroscopy the obtained data allow the deduction of a two-step mechanism of gold nanoparticle formati...

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Topics: Colloidal gold (55%), Small-angle X-ray scattering (51%), Nanoparticle (50%) ... show more

330 Citations

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