The Experts below are selected from a list of 1932 Experts worldwide ranked by ideXlab platform
Benoit Dubertret - One of the best experts on this subject based on the ideXlab platform.
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synthesis of zinc and lead chalcogenide core and core shell Nanoplatelets using sequential cation exchange reactions
Chemistry of Materials, 2014Co-Authors: Cecile Bouet, Donatien Laufer, Benoit Mahler, Brice Nadal, Hadrien Heuclin, Silvia Pedetti, G Patriarche, Benoit DubertretAbstract:We present the synthesis of a novel type of chalcogenide Nanoplatelets. Starting from CdS core or CdSe/CdS core/shell Nanoplatelets, we use sequential cation exchange to copper and then to either zinc or lead to obtain ZnS and PbS core or ZnSe/ZnS and PbSe/PbS core/shell structures. The procedure preserves well the 2D geometry of the Nanoplatelets, provided that they are more than 6 monolayers (∼1.8 nm) thick. The core/shell structure is also well conserved during the cation exchange as verified by TEM images. The Nanoplatelets exchanged with Zn crystallize in a zinc blende structure, like the initial Cd-based material, whereas when Pb is used, the final Nanoplatelets have a rock-salt crystal structure. We explored the copper cation exchange process using energy dispersive X-ray spectrometry with 1 nm resolution on Nanoplatelets standing on their edges, and we show that copper ions diffuse uniformly from the outside of the Nanoplatelet to the inside during the exchange.
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bimolecular auger recombination of electron hole pairs in two dimensional cdse and cdse cdzns core shell Nanoplatelets
Journal of Physical Chemistry Letters, 2013Co-Authors: Lucas T Kunneman, Hadrien Heuclin, Benoit Dubertret, Mickael D Tessier, Yaroslav V Aulin, Ferdinand C Grozema, Juleon M Schins, Laurens D A SiebbelesAbstract:We have determined the Auger recombination kinetics of electrons and holes in colloidal CdSe-only and CdSe/CdS/ZnS core/shell Nanoplatelets by time-resolved photoluminescence measurements. Excitation densities as high as an average of 18 electron–hole pairs per Nanoplatelet were reached. Auger recombination can be described by second-order kinetics. From this we infer that the majority of electrons and holes are bound in the form of neutral excitons, while the fraction of free charges is much smaller. The biexciton Auger recombination rate in Nanoplatelets is more than 1 order of magnitude smaller than for quantum dots and nanorods of equal volume. The latter is of advantage for application in lasers, light-emitting diodes, and photovoltaics.
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continuous transition from 3d to 1d confinement observed during the formation of cdse Nanoplatelets
Journal of the American Chemical Society, 2011Co-Authors: Sandrine Ithurria, Gabriel D Bousquet, Benoit DubertretAbstract:We study the formation of colloidal CdSe Nanoplatelets using both tansmission electron microscopy (TEM) and spectroscopic analysis. We show that the platelets form by continuous lateral extension of small (<2 nm) nanocrystal CdSe seeds. The Nanoplatelet thickness is fixed by the seed dimension and remains constant during the platelet formation. The Nanoplatelet lateral dimensions can be tuned using additional precursor injection. Absorption and fluorescence analysis of the CdSe Nanoplatelets as they continuously extend laterally confirms a continuous transition from 3D to 1D confined nanoparticles. The formation of the CdSe platelets is found to be similar for different platelet thicknesses that we control with a precision of one CdSe monolayer.
Benjamin T Diroll - One of the best experts on this subject based on the ideXlab platform.
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semiconductor Nanoplatelet excimers
Nano Letters, 2018Co-Authors: Benjamin T Diroll, Igor Coropceanu, Nicholas Holtgrewe, Michael R Wasielewski, Vitali B Prakapenka, Samantha M Harvey, Alexandra Brumberg, Scott A. Crooker, Dmitri V Talapin, Richard D SchallerAbstract:Excimers, a portmanteau of “excited dimer”, are transient species that are formed from the electronic interaction of a fluorophore in the excited state with a neighbor in the ground state, which have found extensive use as laser gain media. Although common in molecular fluorophores, this work presents evidence for the formation of excimers in a new class of materials: atomically precise two-dimensional semiconductor Nanoplatelets. Colloidal Nanoplatelets of CdSe display two-color photoluminescence resolved at low temperatures with one band attributed to band-edge fluorescence and a second, red band attributed to excimer fluorescence. Previously reasonable explanations for two-color fluorescence, such as charging, are shown to be inconsistent with additional evidence. As with excimers in other materials systems, excimer emission is increased by increasing Nanoplatelet concentration and the degree of cofacial stacking. Consistent with their promise as low-threshold gain media, amplified spontaneous emission...
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semiconductor Nanoplatelet excimers
Nano Letters, 2018Co-Authors: Benjamin T Diroll, Igor Coropceanu, Nicholas Holtgrewe, Michael R Wasielewski, Vitali B Prakapenka, Samantha M Harvey, Alexandra Brumberg, Scott A. Crooker, Wooje Cho, Dmitri V TalapinAbstract:Excimers, a portmanteau of "excited dimer", are transient species that are formed from the electronic interaction of a fluorophore in the excited state with a neighbor in the ground state, which have found extensive use as laser gain media. Although common in molecular fluorophores, this work presents evidence for the formation of excimers in a new class of materials: atomically precise two-dimensional semiconductor Nanoplatelets. Colloidal Nanoplatelets of CdSe display two-color photoluminescence resolved at low temperatures with one band attributed to band-edge fluorescence and a second, red band attributed to excimer fluorescence. Previously reasonable explanations for two-color fluorescence, such as charging, are shown to be inconsistent with additional evidence. As with excimers in other materials systems, excimer emission is increased by increasing Nanoplatelet concentration and the degree of cofacial stacking. Consistent with their promise as low-threshold gain media, amplified spontaneous emission emerges from the excimer emission line.
Beatriz Martingarcia - One of the best experts on this subject based on the ideXlab platform.
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core shell cdse cds bone shaped nanocrystals with a thick and anisotropic shell as optical emitters
Advanced Optical Materials, 2020Co-Authors: Andrea Castelli, Balaji Dhanabalan, Anatolii Polovitsyn, Vincenzo Caligiuri, Francesco Di Stasio, Milan Palei, Alice Scarpellini, Rosaria Brescia, Beatriz MartingarciaAbstract:Colloidal core/shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe Nanoplatelet seeds and obtain bone-shaped heterostructures with a highly anisotropic shell. Surprisingly, the Nanoplatelets withstand the high growth temperature of 350 °C and we obtain structures with a CdSe Nanoplatelet core that is overcoated by a shell of cubic CdS, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/shell nanocrystals show a bandedge emission around 657 nm with a photoluminescence quantum yield of ca. 42 % in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission, and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. Our work stimulates the design and fabrication of more exotic core/shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered.
Balaji Dhanabalan - One of the best experts on this subject based on the ideXlab platform.
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core shell cdse cds bone shaped nanocrystals with a thick and anisotropic shell as optical emitters
Advanced Optical Materials, 2020Co-Authors: Andrea Castelli, Balaji Dhanabalan, Anatolii Polovitsyn, Vincenzo Caligiuri, Francesco Di Stasio, Milan Palei, Alice Scarpellini, Rosaria Brescia, Beatriz MartingarciaAbstract:Colloidal core/shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe Nanoplatelet seeds and obtain bone-shaped heterostructures with a highly anisotropic shell. Surprisingly, the Nanoplatelets withstand the high growth temperature of 350 °C and we obtain structures with a CdSe Nanoplatelet core that is overcoated by a shell of cubic CdS, on top of which tetrahedral CdS structures with hexagonal lattice are formed. These complex core/shell nanocrystals show a bandedge emission around 657 nm with a photoluminescence quantum yield of ca. 42 % in solution, which is also retained in thin films. Interestingly, the nanocrystals manifest simultaneous red and green emission, and the relatively long wavelength of the green emission indicates charge recombination at the cubic/hexagonal interface of the CdS shell. The nanocrystal films show amplified spontaneous emission, random lasing, and distributed feedback lasing when the material is deposited on suitable gratings. Our work stimulates the design and fabrication of more exotic core/shell heterostructures where charge carrier delocalization, dipole moment, and other optical and electrical properties can be engineered.
Konstantinos Chrissafis - One of the best experts on this subject based on the ideXlab platform.
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kinetics of crystallization and thermal degradation of an isotactic polypropylene matrix reinforced with graphene glass fiber filler
Molecules, 2019Co-Authors: Evangelia Tarani, George Z. Papageorgiou, Dimitrios N. Bikiaris, Konstantinos ChrissafisAbstract:Polypropylene composites reinforced with a filler mixture of graphene Nanoplatelet-glass fiber were prepared by melt mixing, while conventional composites containing graphene Nanoplatelet and glass fiber were prepared for comparative reasons. An extensive study of thermally stimulated processes such as crystallization, nucleation, and kinetics was carried out using Differential Scanning Calorimetry and Thermogravimetric Analysis. Moreover, effective activation energy and kinetic parameters of the thermal decomposition process were determined by applying Friedman's isoconversional differential method and multivariate non-linear regression method. It was found that the graphene Nanoplatelets act positively towards the increase in crystallization rate and nucleation phenomena under isothermal conditions due to their large surface area, inherent nucleation activity, and high filler content. Concerning the thermal degradation kinetics of polypropylene graphene Nanoplatelets/glass fibers composites, a change in the decomposition mechanism of the matrix was found due to the presence of graphene Nanoplatelets. The effect of graphene Nanoplatelets dominates that of the glass fibers, leading to an overall improvement in performance.
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Kinetics of Crystallization and Thermal Degradation of an Isotactic Polypropylene Matrix Reinforced with Graphene/Glass-Fiber Filler
MDPI AG, 2019Co-Authors: Evangelia Tarani, George Z. Papageorgiou, Dimitrios N. Bikiaris, Konstantinos ChrissafisAbstract:Polypropylene composites reinforced with a filler mixture of graphene Nanoplatelet-glass fiber were prepared by melt mixing, while conventional composites containing graphene Nanoplatelet and glass fiber were prepared for comparative reasons. An extensive study of thermally stimulated processes such as crystallization, nucleation, and kinetics was carried out using Differential Scanning Calorimetry and Thermogravimetric Analysis. Moreover, effective activation energy and kinetic parameters of the thermal decomposition process were determined by applying Friedman’s isoconversional differential method and multivariate non-linear regression method. It was found that the graphene Nanoplatelets act positively towards the increase in crystallization rate and nucleation phenomena under isothermal conditions due to their large surface area, inherent nucleation activity, and high filler content. Concerning the thermal degradation kinetics of polypropylene graphene Nanoplatelets/glass fibers composites, a change in the decomposition mechanism of the matrix was found due to the presence of graphene Nanoplatelets. The effect of graphene Nanoplatelets dominates that of the glass fibers, leading to an overall improvement in performance
