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Size-Tunable Manganese-Doped Spheroidal CsPbCl 3 Quantum Dots. J Phys Chem Lett 2024; 15:3728-3732. [PMID: 38546986 DOI: 10.1021/acs.jpclett.4c00049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2024]
Abstract
Manganese doping has been demonstrated as a versatile tool to tune the emission of CsPbCl3 nanocrystals (NCs). Although this has been demonstrated in nanocubes and nanoplatelets, strategies for doping Mn2+ in size-tunable, excitonic CsPbCl3 quantum dots (QDs) remain absent. In this work, we demonstrate the synthesis of size-tunable spheroidal CsPbCl3:Mn2+ QDs, which can be obtained by a water-hexane interfacial combined anion and cation exchange strategy starting from CsPbBr3 QDs. Interestingly, the QDs exhibit a fast 0.2 ms Mn2+ photoluminescence (PL) lifetime and an energy transfer (ET) time of approximately 100 ps from the excitonic state of the QD to the atomic state of the Mn2+ ion. The size dependence observation of the manganese PL efficiency and the slow ET rate suggest that Mn2+ mainly gets incorporated at the QD's surface, highlighting the importance of strategies chosen for the incorporation of Mn2+ into perovskite QDs.
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A Bound Exciton Resonance Modulated by Bulk and Localized Coherent Phonons in Double Perovskites. J Phys Chem Lett 2024; 15:2169-2176. [PMID: 38373052 DOI: 10.1021/acs.jpclett.3c03443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2024]
Abstract
Optically excited electronic excitations are coupled to the soft and polar halide perovskite lattice, generating coherent phonons after subpicosecond interband laser-excitation. In Ag-based halide double perovskites, Ag-vacancies can bind free excitons, resulting in a pronounced bound exciton resonance. Here, we report the detection of three modulation frequencies corresponding to coherent phonons in Ag-based double perovskite nanocrystals at distinct spectral positions at the bound exciton resonance. Two of them are found in oscillatory spectral shifts of the bound exciton resonance and are identified as Cs- and Br-related bulk phonons. Surprisingly, a third frequency is observed as an intensity modulation. We argue that this amplitude oscillation is a consequence of an optically generated vibronic wave packet localized at a Ag-vacancy. Consequently, the localized coherent phonon modulates the giant oscillator strength of the bound exciton. This optically induced and spatially localized lattice shaking could potentially be useful for initiating photochemical reactions with atomic precision.
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Abstract
Postsynthetic metal salt treatments are frequently employed in the luminescence enhancement of quantum dots (QDs); however, its microscopic picture remains unclear. CsPbBr3-QDs, featuring strong excitonic absorption and high photoluminescence (PL) quantum yield, are ideal QDs to unravel the intricate interaction between QDs and such surface-bound metal salts. Herein, we study this interaction based on the controlled PL quenching of CsPbBr3-QDs with BiBr3. Upon the addition of BiBr3, an instant and complete PL quenching is observed, which can be fully recovered after the addition of an excess of PbBr2. This, together with the complete preservation of the excitonic absorption suggests a surface-driven adsorption equilibrium. Additionally, time-resolved studies reveal a non-homogeneous surface trap formation. Based on the so-called sphere of action model for the adsorption process, we show that already a single BiBr3 adsorption suffices to completely quench a QD's luminescence. This approach is expanded to analyze size-, ligand-, and metal-dependent quenching dynamics. Facet junctions are identified as regions of enhanced surface reactivity. A Langmuir-type ligand coverage is exposed with a strong impact on adsorption. Our results provide a detailed mechanistic insight into postsynthetic interaction of QDs with metal salts, opening pathways for future surface manipulations.
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Growth and Self-Assembly of CsPbBr 3 Nanocrystals in the TOPO/PbBr 2 Synthesis as Seen with X-ray Scattering. NANO LETTERS 2023; 23:667-676. [PMID: 36607192 PMCID: PMC9881167 DOI: 10.1021/acs.nanolett.2c04532] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Despite broad interest in colloidal lead halide perovskite nanocrystals (LHP NCs), their intrinsic fast growth has prevented controlled synthesis of small, monodisperse crystals and insights into the reaction mechanism. Recently, a much slower synthesis of LHP NCs with extreme size control has been reported, based on diluted TOPO/PbBr2 precursors and a diisooctylphosphinate capping ligand. We report new insights into the nucleation, growth, and self-assembly in this reaction, obtained by in situ synchrotron-based small-angle X-ray scattering and optical absorption spectroscopy. We show that dispersed 3 nm Cs[PbBr3] agglomerates are the key intermediate species: first, they slowly nucleate into crystals, and then they release Cs[PbBr3] monomers for further growth of the crystals. We show the merits of a low Cs[PbBr3] monomer concentration for the reaction based on oleate ligands. We also examine the spontaneous superlattice formation mechanism occurring when the growing nanocrystals in the solvent reach a critical size of 11.6 nm.
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Abstract
Quantum dots (QDs) offer unique physical properties and novel application possibilities like single-photon emitters for quantum technologies. While strongly confined III-V and II-VI QDs have been studied extensively, their complex valence band structure often limits clear observations of individual transitions. In recently emerged lead-halide perovskites, band degeneracies are absent around the bandgap reducing the complexity of optical spectra. We show that for spherical-like CsPbBr3 QDs with diameters >6 nm, excitons confine with respect to their center-of-mass motion leading to well-pronounced resonances in their absorption spectra. Optical pumping of the lowest-confined exciton with femtosecond laser pulses not only bleaches all excitons but also reveals a series of distinct induced absorption resonances which we attribute to exciton-to-biexciton transitions and are red-shifted by the biexciton binding energy (∼40 meV). The temporal dynamics of the bleached excitons further support our exciton confinement model. Our study provides the first insight into confined excitons in CsPbBr3 QDs and gives a detailed understanding of their linear and nonlinear optical spectra.
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Spheroidal Cesium Lead Chloride-Bromide Quantum Dots and a Fast Determination of Their Size and Halide Content. NANO LETTERS 2022; 22:8168-8173. [PMID: 36215299 DOI: 10.1021/acs.nanolett.2c02601] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Lead halide perovskite (LHP) quantum dots (QDs), with their bright and narrow emission, are promising candidates for LEDs, lasers, and quantum light sources. However, current methods to synthesize monodisperse CsPb(Cl:Br)3 and CsPbCl3 QDs exhibiting multiple sharp absorption resonances are not as well developed compared to CsPbBr3. Furthermore, both quantum confinement and the halide ratio in CsPb(Cl:Br)3 QDs strongly influence the bandgap, making it impossible to optically determine their size. In this work, monodisperse spheroidal CsPb(Cl:Br)3 QDs are synthesized in the 4-10 nm range, at any Cl:Br ratio, with up to five excitonic absorption transitions. Furthermore, in situ spectroscopy was used to cross-correlate the size and composition of these QDs directly to the energy of the first two excitonic absorption transitions. This work therefore provides not only a method for monodisperse CsPb(Cl:Br)3 QDs but also a protocol to determine their size, concentration, and halide ratio, circumventing conventional expensive and time-consuming techniques.
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Abstract
Colloidal lead halide perovskite (LHP) nanocrystals are of interest as photoluminescent quantum dots (QDs) whose properties depend on the size and shape. They are normally synthesized on subsecond time scales through hard-to-control ionic metathesis reactions. We report a room-temperature synthesis of monodisperse, isolable spheroidal APbBr3 QDs (A=Cs, formamidinium, methylammonium) that are size-tunable from 3 to over 13 nanometers. The kinetics of both nucleation and growth are temporally separated and drastically slowed down by the intricate equilibrium between the precursor (PbBr2) and the A[PbBr3] solute, with the latter serving as a monomer. QDs of all these compositions exhibit up to four excitonic transitions in their linear absorption spectra, and we demonstrate that the size-dependent confinement energy for all transitions is independent of the A-site cation.
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Exploiting the Lability of Metal Halide Perovskites for Doping Semiconductor Nanocomposites. ACS ENERGY LETTERS 2021; 6:581-587. [PMID: 33614964 PMCID: PMC7887873 DOI: 10.1021/acsenergylett.0c02448] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 01/11/2021] [Indexed: 05/31/2023]
Abstract
Cesium lead halides have intrinsically unstable crystal lattices and easily transform within perovskite and nonperovskite structures. In this work, we explore the conversion of the perovskite CsPbBr3 into Cs4PbBr6 in the presence of PbS at 450 °C to produce doped nanocrystal-based composites with embedded Cs4PbBr6 nanoprecipitates. We show that PbBr2 is extracted from CsPbBr3 and diffuses into the PbS lattice with a consequent increase in the concentration of free charge carriers. This new doping strategy enables the adjustment of the density of charge carriers between 1019 and 1020 cm-3, and it may serve as a general strategy for doping other nanocrystal-based semiconductors.
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Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures. J Am Chem Soc 2020; 142:10198-10211. [PMID: 32374173 PMCID: PMC7737912 DOI: 10.1021/jacs.0c03577] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2020] [Indexed: 11/28/2022]
Abstract
We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on Pb4S3Br2, a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS-PbBr2 phase diagram. The Pb4S3Br2 nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to ∼30 nm), an indirect bandgap, photoconductivity (responsivity = 4 ± 1 mA/W), and stability for months in air. A crystal structure is proposed for this new material by combining the information from 3D electron diffraction and electron tomography of a single nanocrystal, X-ray powder diffraction, and density functional theory calculations. Such a structure is closely related to that of the recently discovered high-pressure chalcohalide Pb4S3I2 phase, and indeed we were able to extend our synthesis scheme to Pb4S3I2 colloidal nanocrystals, whose structure matches the one that has been published for the bulk. Finally, we could also prepare nanocrystals of Pb3S2Cl2, which proved to be a structural analogue of the recently reported bulk Pb3Se2Br2 phase. It is remarkable that one high-pressure structure (for Pb4S3I2) and two metastable structures that had not yet been reported (for Pb4S3Br2 and Pb3S2Cl2) can be prepared on the nanoscale by wet-chemical approaches. This highlights the important role of colloidal chemistry in the discovery of new materials and motivates further exploration into metal chalcohalide nanocrystals.
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What Defines a Halide Perovskite? ACS ENERGY LETTERS 2020; 5:604-610. [PMID: 33344766 PMCID: PMC7739487 DOI: 10.1021/acsenergylett.0c00039] [Citation(s) in RCA: 80] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Accepted: 01/17/2020] [Indexed: 05/05/2023]
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Green-Emitting Powders of Zero-Dimensional Cs 4PbBr 6: Delineating the Intricacies of the Synthesis and the Origin of Photoluminescence. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2019; 31:7761-7769. [PMID: 32952293 PMCID: PMC7116092 DOI: 10.1021/acs.chemmater.9b02944] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
A detailed investigation into the synthesis of green-emitting powders of Cs4PbBr6 and CsPbBr3 materials by antisolvent precipitation from CsBr-PbBr2 precursor solutions in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is reported. Various solvated lead bromide and polybromide species (PbBr2, [PbBr3]-, [PbBr4]2-, and possibly [PbBr5]3-or [PbBr6]4-) are detected in the precursor solutions by optical absorbance and emission spectroscopies. The solvodynamic size of the species in solution is strongly solvent-dependent: ~1 nm species were detected in DMSO, while significantly larger species were observed in DMF by dynamic light scattering. The solvodynamic size of the lead bromide species plays a critical role in determining the Cs-Pb-Br composition of the precipitated powders: smaller species favor the precipitation of Cs4PbBr6, while larger species template the formation of CsPbBr3 under identical experimental conditions. The powders have been characterized by 133Cs and 207Pb solid-state nuclear magnetic resonance, and 133Cs sensitivity toward the different Cs environments within Cs4PbBr6 is demonstrated. Finally, the possible origins of green emission in Cs4PbBr6 samples are discussed. It is proposed that a two-dimensional Cs2PbBr4 inclusion may be responsible for green emission at ~520 nm in addition to the widely acknowledged CsPbBr3 impurity, although we found no conclusive experimental evidence supporting such claims.
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Ultrafast THz Probe of Photoinduced Polarons in Lead-Halide Perovskites. PHYSICAL REVIEW LETTERS 2019; 122:166601. [PMID: 31075027 DOI: 10.1103/physrevlett.122.166601] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 03/01/2019] [Indexed: 06/09/2023]
Abstract
We study the nature of photoexcited charge carriers in CsPbBr_{3} nanocrystal thin films by ultrafast optical pump-THz probe spectroscopy. We observe a deviation from a pure Drude dispersion of the THz dielectric response that is ascribed to the polaronic nature of carriers; a transient blueshift of observed phonon frequencies is indicative of the coupling between photogenerated charges and stretching-bending modes of the deformed inorganic sublattice, as confirmed by DFT calculations.
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The Phosphine Oxide Route toward Lead Halide Perovskite Nanocrystals. J Am Chem Soc 2018; 140:14878-14886. [PMID: 30358392 PMCID: PMC6438589 DOI: 10.1021/jacs.8b08978] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Indexed: 12/18/2022]
Abstract
We report an amine-free synthesis of lead halide perovskite (LHP) nanocrystals, using trioctylphosphine oxide (TOPO) instead of aliphatic amines, in combination with a protic acid (e.g., oleic acid). The overall synthesis scheme bears many similarities to the chemistry behind the preparation of LHP thin films and single crystals, in terms of ligand coordination to the chemical precursors. The acidity of the environment and hence the extent of protonation of the TOPO molecules tune the reactivity of the PbX2 precursor, regulating the size of the nanocrystals. On the other hand, TOPO molecules are virtually absent from the surface of our nanocrystals, which are simply passivated by one type of ligand (e.g., Cs-oleate). Furthermore, our studies reveal that Cs-oleate is dynamically bound to the surface of the nanocrystals and that an optimal surface coverage is critical for achieving high photoluminescence quantum yield. Our scheme delivers NCs with a controlled size and shape: only cubes are formed, with no contamination with platelets, regardless of the reaction conditions that were tested. We attribute such a shape homogeneity to the absence of primary aliphatic amines in our reaction environment, since these are known to promote the formation of nanocrystals with sheet/platelet morphologies or layered phases under certain reaction conditions. The TOPO route is particularly appealing with regard to synthesizing LHP nanocrystals for large-scale manufacturing, as the yield in terms of material produced is close to the theoretical limit: i.e., almost all precursors employed in the synthesis are converted into nanocrystals.
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Anisotropic 2D Cu 2-x Se Nanocrystals from Dodecaneselenol and Their Conversion to CdSe and CuInSe 2 Nanoparticles. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2018; 30:3836-3846. [PMID: 29910536 PMCID: PMC6002073 DOI: 10.1021/acs.chemmater.8b01143] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2018] [Revised: 05/09/2018] [Indexed: 05/28/2023]
Abstract
We present the synthesis of colloidal anisotropic Cu2-x Se nanocrystals (NCs) with excellent size and shape control, using the unexplored phosphine-free selenium precursor 1-dodecaneselenol (DDSe). This precursor forms lamellar complexes with Cu(I) that enable tailoring the NC morphology from 0D polyhedral to highly anisotropic 2D shapes. The Cu2-x Se NCs are subsequently used as templates in postsynthetic cation exchange reactions, through which they are successfully converted to CdSe and CuInSe2 quantum dots, nanoplatelets, and ultrathin nanosheets. The shape of the template hexagonal nanoplatelets is preserved during the cation exchange reaction, despite a substantial reorganization of the anionic sublattice, which leads to conversion of the tetragonal umangite crystal structure of the parent Cu2-x Se NCs into hexagonal wurtzite CdSe and CuInSe2, accompanied by a change of both the thickness and the lateral dimensions of the nanoplatelets. The crystallographic transformation and reconstruction of the product NCs are attributed to a combination of the unit cell dimensionalities of the parent and product crystal phases and an internal ripening process. This work provides novel tools for the rational design of shape-controlled colloidal anisotropic Cu2-x Se NCs, which, besides their promising optoelectronic properties, also constitute a new family of cation exchange templates for the synthesis of shape-controlled NCs of wurtzite CdSe, CuInSe2, and other metal selenides that cannot be attained through direct synthesis approaches. Moreover, the insights provided here are likely applicable also to the direct synthesis of shape-controlled NCs of other metal selenides, since DDSe may be able to form lamellar complexes with several other metals.
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Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals. NATURE MATERIALS 2018; 17:394-405. [PMID: 29459748 DOI: 10.1038/s41563-018-0018-4] [Citation(s) in RCA: 736] [Impact Index Per Article: 122.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2017] [Accepted: 01/08/2018] [Indexed: 05/18/2023]
Abstract
Lead halide perovskites (LHPs) in the form of nanometre-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same experimental mindset and theoretical framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.
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Doped Halide Perovskite Nanocrystals for Reabsorption-Free Luminescent Solar Concentrators. ACS ENERGY LETTERS 2017; 2:2368-2377. [PMID: 31206029 PMCID: PMC6559125 DOI: 10.1021/acsenergylett.7b00701] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 09/11/2017] [Indexed: 05/17/2023]
Abstract
Halide perovskite nanocrystals (NCs) are promising solution-processed emitters for low-cost optoelectronics and photonics. Doping adds a degree of freedom for their design and enables us to fully decouple their absorption and emission functions. This is paramount for luminescent solar concentrators (LSCs) that enable fabrication of electrode-less solar windows for building-integrated photovoltaic applications. Here, we demonstrate the suitability of manganese-doped CsPbCl3 NCs as reabsorption-free emitters for large-area LSCs. Light propagation measurements and Monte Carlo simulations indicate that the dopant emission is unaffected by reabsorption. Nanocomposite LSCs were fabricated via mass copolymerization of acrylate monomers, ensuring thermal and mechanical stability and optimal compatibility of the NCs, with fully preserved emission efficiency. As a result, perovskite LSCs behave closely to ideal devices, in which all portions of the illuminated area contribute equally to the total optical power. These results demonstrate the potential of doped perovskite NCs for LSCs, as well as for other photonic technologies relying on low-attenuation long-range optical wave guiding.
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Low-Temperature Electron Beam-Induced Transformations of Cesium Lead Halide Perovskite Nanocrystals. ACS OMEGA 2017; 2:5660-5665. [PMID: 28983524 PMCID: PMC5623946 DOI: 10.1021/acsomega.7b01009] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 08/22/2017] [Indexed: 05/21/2023]
Abstract
Cesium lead halide perovskite (CsPbX3, with X = Br, Cl, I) nanocrystals have been found to undergo severe modifications under the high-energy electron beam irradiation of a transmission electron microscope (80/200 keV). In particular, in our previous work, together with halogen desorption, Pb2+ ions were found to be reduced to Pb0 and then diffused to form lead nanoparticles at temperatures above -40 °C. Here, we present a detailed irradiation study of CsPbBr3 nanocrystals at temperatures below -40 °C, a range in which the diffusion of Pb0 atoms/clusters is drastically suppressed. Under these conditions, the irradiation instead induces the nucleation of randomly oriented CsBr, CsPb, and PbBr2 crystalline domains. In addition to the Br desorption, which accompanies Pb2+ reduction at all the temperatures, Br is also desorbed from the CsBr and PbBr2 domains at low temperatures, leading to a more pronounced Br loss, thus the final products are mainly composed of Cs and Pb. The overall transformation involves the creation of voids, which coalesce upon further exposure, as demonstrated in both nanosheets and nanocuboids. Our results show that although low temperatures hinder the formation of Pb nanoparticles in CsPbBr3 nanocrystals when irradiated, the nanocrystals are nevertheless unstable. Consequently, we suggest that an optimum combination of temperature range, electron energy, and dose rate needs to be carefully chosen for the characterization of halide perovskite nanocrystals to minimize both the Pb nanoparticle formation and the structural decomposition.
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Reversible Concentration-Dependent Photoluminescence Quenching and Change of Emission Color in CsPbBr 3 Nanowires and Nanoplatelets. J Phys Chem Lett 2017; 8:2725-2729. [PMID: 28581755 DOI: 10.1021/acs.jpclett.7b01305] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We discuss the photoluminescence (PL) of quantum-confined CsPbBr3 colloidal nanocrystals of two different shapes (nanowires and nanoplatelets) at different concentrations in solution and in solid-state films. Upon increasing the nanocrystal concentration in solution, a constant drop in photoluminescence quantum yield is observed, accompanied by a significant PL red shift. This effect is reversible, and the original PL can be restored by diluting to the original concentration. We show that this effect can be in part attributed to self-absorption and partly to aggregation. In particular, for nanoplatelets, where the aggregation is mostly irreversible, while the self-absorption effect is reversible, the two contributions can be well separated. Finally, when dry solid-state films are prepared, the emission band is shifted into the green spectral region, close to the bulk CsPbBr3 band gap, thus preventing blue emission from such films.
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Changing the Dimensionality of Cesium Lead Bromide Nanocrystals by Reversible Postsynthesis Transformations with Amines. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2017; 29:4167-4171. [PMID: 28572702 PMCID: PMC5445717 DOI: 10.1021/acs.chemmater.7b00895] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 04/01/2017] [Indexed: 05/20/2023]
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Nearly Monodisperse Insulator Cs 4PbX 6 (X = Cl, Br, I) Nanocrystals, Their Mixed Halide Compositions, and Their Transformation into CsPbX 3 Nanocrystals. NANO LETTERS 2017; 17:1924-1930. [PMID: 28196323 PMCID: PMC5345893 DOI: 10.1021/acs.nanolett.6b05262] [Citation(s) in RCA: 230] [Impact Index Per Article: 32.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
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. The Cs4PbBr6 nanocrystals can be converted into green fluorescent CsPbBr3 nanocrystals by their reaction with an excess of PbBr2 with preservation of size and size distributions. The insertion of PbX2 into Cs4PbX6 provides a means of accessing CsPbX3 nanocrystals in a wide variety of sizes, shapes, and compositions, an important aspect for the development of precisely tuned perovskite nanocrystal inks.
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In Situ Transmission Electron Microscopy Study of Electron Beam-Induced Transformations in Colloidal Cesium Lead Halide Perovskite Nanocrystals. ACS NANO 2017; 11:2124-2132. [PMID: 28122188 PMCID: PMC5345894 DOI: 10.1021/acsnano.6b08324] [Citation(s) in RCA: 110] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 01/25/2017] [Indexed: 05/20/2023]
Abstract
An increasing number of studies have recently reported the rapid degradation of hybrid and all-inorganic lead halide perovskite nanocrystals under electron beam irradiation in the transmission electron microscope, with the formation of nanometer size, high contrast particles. The nature of these nanoparticles and the involved transformations in the perovskite nanocrystals are still a matter of debate. Herein, we have studied the effects of high energy (80/200 keV) electron irradiation on colloidal cesium lead bromide (CsPbBr3) nanocrystals with different shapes and sizes, especially 3 nm thick nanosheets, a morphology that facilitated the analysis of the various ongoing processes. Our results show that the CsPbBr3 nanocrystals undergo a radiolysis process, with electron stimulated desorption of a fraction of bromine atoms and the reduction of a fraction of Pb2+ ions to Pb0. Subsequently Pb0 atoms diffuse and aggregate, giving rise to the high contrast particles, as previously reported by various groups. The diffusion is facilitated by both high temperature and electron beam irradiation. The early stage Pb nanoparticles are epitaxially bound to the parent CsPbBr3 lattice, and evolve into nonepitaxially bound Pb crystals upon further irradiation, leading to local amorphization and consequent dismantling of the CsPbBr3 lattice. The comparison among CsPbBr3 nanocrystals with various shapes and sizes evidences that the damage is particularly pronounced at the corners and edges of the surface, due to a lower diffusion barrier for Pb0 on the surface than inside the crystal and the presence of a larger fraction of under-coordinated atoms.
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Nonlinear Carrier Interactions in Lead Halide Perovskites and the Role of Defects. J Am Chem Soc 2016; 138:13604-13611. [DOI: 10.1021/jacs.6b06463] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Polymer-Free Films of Inorganic Halide Perovskite Nanocrystals as UV-to-White Color-Conversion Layers in LEDs. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2016; 28:2902-2906. [PMID: 27563171 PMCID: PMC4993521 DOI: 10.1021/acs.chemmater.6b00954] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 04/05/2016] [Indexed: 05/23/2023]
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Solution Synthesis Approach to Colloidal Cesium Lead Halide Perovskite Nanoplatelets with Monolayer-Level Thickness Control. J Am Chem Soc 2016; 138:1010-6. [PMID: 26726764 PMCID: PMC4731826 DOI: 10.1021/jacs.5b12124] [Citation(s) in RCA: 363] [Impact Index Per Article: 45.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
We report a colloidal synthesis approach to CsPbBr3 nanoplatelets (NPLs). The nucleation and growth of the platelets, which takes place at room temperature, is triggered by the injection of acetone in a mixture of precursors that would remain unreactive otherwise. The low growth temperature enables the control of the plate thickness, which can be precisely tuned from 3 to 5 monolayers. The strong two-dimensional confinement of the carriers at such small vertical sizes is responsible for a narrow PL, strong excitonic absorption, and a blue shift of the optical band gap by more than 0.47 eV compared to that of bulk CsPbBr3. We also show that the composition of the NPLs can be varied all the way to CsPbBr3 or CsPbI3 by anion exchange, with preservation of the size and shape of the starting particles. The blue fluorescent CsPbCl3 NPLs represent a new member of the scarcely populated group of blue-emitting colloidal nanocrystals. The exciton dynamics were found to be independent of the extent of 2D confinement in these platelets, and this was supported by band structure calculations.
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Abstract
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We demonstrate that, via controlled
anion exchange reactions using
a range of different halide precursors, we can finely tune the chemical
composition and the optical properties of presynthesized colloidal
cesium lead halide perovskite nanocrystals (NCs), from green emitting
CsPbBr3 to bright emitters in any other region of the visible
spectrum, and back, by displacement of Cl– or I– ions and reinsertion of Br– ions.
This approach gives access to perovskite semiconductor NCs with both
structural and optical qualities comparable to those of directly synthesized
NCs. We also show that anion exchange is a dynamic process that takes
place in solution between NCs. Therefore, by mixing solutions containing
perovskite NCs emitting in different spectral ranges (due to different
halide compositions) their mutual fast exchange dynamics leads to
homogenization in their composition, resulting in NCs emitting in
a narrow spectral region that is intermediate between those of the
parent nanoparticles.
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From Binary Cu2S to ternary Cu-In-S and quaternary Cu-In-Zn-S nanocrystals with tunable composition via partial cation exchange. ACS NANO 2015; 9:521-31. [PMID: 25551255 DOI: 10.1021/nn505786d] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We present an approach for the synthesis of ternary copper indium sulfide (CIS) and quaternary copper indium zinc sulfide (CIZS) nanocrystals (NCs) by means of partial cation exchange with In(3+) and Zn(2+). The approach consists of a sequential three-step synthesis: first, binary Cu2S NCs were synthesized, followed by the homogeneous incorporation of In(3+) by an in situ partial cation-exchange reaction, leading to CIS NCs. In the last step, a second partial exchange was performed where Zn(2+) partially replaced the Cu(+) and In(3+) cations at the surface, creating a ZnS-rich shell with the preservation of the size and shape. By careful tuning reaction parameters (growth and exchange times as well as the initial Cu(+):In(3+):Zn(2+) ratios), control over both the size and composition was achieved. This led to a broad tuning of photoluminescence of the final CIZS NCs, ranging from 880 to 1030 nm without altering the NCs size. Cytotoxicity tests confirmed the biocompatibility of the synthesized CIZS NCs, which opens up opportunities for their application as near-infrared fluorescent markers in the biomedical field.
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Self-assembly of colloidal hexagonal bipyramid- and bifrustum-shaped ZnS nanocrystals into two-dimensional superstructures. NANO LETTERS 2014; 14:1032-7. [PMID: 24433112 DOI: 10.1021/nl4046069] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We present a combined experimental, theoretical, and simulation study on the self-assembly of colloidal hexagonal bipyramid- and hexagonal bifrustum-shaped ZnS nanocrystals (NCs) into two-dimensional superlattices. The simulated NC superstructures are in good agreement with the experimental ones. This shows that the self-assembly process is primarily driven by minimization of the interfacial free-energies and maximization of the packing density. Our study shows that a small truncation of the hexagonal bipyramids is sufficient to change the symmetry of the resulting superlattice from hexagonal to tetragonal, highlighting the crucial importance of precise shape control in the fabrication of functional metamaterials by self-assembly of colloidal NCs.
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