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Monodisperse gold cuboctahedral nanocrystals directly synthesized in reverse micelles: Preparation, colloidal dispersion in organic solvents and water, reversible self-assembly and plasmonic properties
摘要： The synthesis of organic-solvent-dispersible gold nanoparticles in reverse micelles of didodecyldimethylammonium bromide (DDAB) is revisited in the present investigation. Some parameters of synthesis, specifically the reaction volume and the concentration of the reducing agent, were slightly modified obtaining directly monodisperse gold nanocrystals (AuNCs) without the need to use additional active surfactants or additional treatments such as digestive ripening. Interestingly, most of the obtained AuNCs display the same exposed crystalline faces composed of six bounding facets (four {111} faces and two {002} faces), corresponding to single-crystalline face-centered cubic (fcc) nanoparticles with a cuboctahedron shape. When these AuNCs are subsequently functionalized with 1-decanethiol (C10H21SH) or 1-dodecanethiol (C12H25SH) they don′t experience significant changes in their size or crystalline texture, however, they self-aggregate directly in the suspension at room temperature into faceted supramolecular structures, and exhibit collective plasmonic excitations. Such self-organization is reversible under heating treatments allowing the observation of the influence of the AuNCs aggregation state on their plasmonic properties. Fast Fourier infrared spectroscopy reveals that thiols only replace partially the DDAB molecules, thus, DDAB molecules remain present in the thiol-capped AuNCs. In order to turn the thiol-capped nanocrystals into water-dispersible nanocrystals and extend their technological potential, they are stabilized with poloxamer 407 obtaining highly stable purple colloids in water.
关键词： collective behaviors,gold,self-assembly,supramolecular structures,nanocrystals
更新于2025-09-12 10:27:22
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Stronger Reductive Environment in Solvothermal Synthesis Leads to Improved Ga Doping Efficiency in ZnO Nanocrystals and Enhanced Plasmonic Absorption
摘要： The key parameter for degenerated semiconductor oxide plasmonic nanocrystals is the doping level. Hydrothermal and solvothermal approaches are considered to be less effective toward achieving high concentration of aliovalent donor dopants in a host oxide when compared to other synthesis methods that use long chain hydrocarbon solvents, fatty acids, and fatty amines as precursors. Because of this, although they have several advantages such as sustainability, ease of use, relatively inexpensive reagents and apparatus, and reduced environmental impact, they are excluded from the list of potential synthesis methods. Herein, an effective Zn2+ substitution with aliovalent Ga3+ in the ZnO host lattice is demonstrated, and it is achieved by increasing the reductive power of the solvothermal synthesis conditions by either solvent substitution or the addition of reducing agents. This increase results in an increased oxidation affinity of the medium. This in turn promotes Ga3+ incorporation into the ZnO lattice, by skewing the reaction equilibrium toward oxygen evolution.
关键词： plasmonic resonance,semiconductor nanocrystals,gallium-doped zinc oxide,degenerated oxide semiconductor nanocrystals
更新于2025-09-11 14:15:04
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A Layered Photo-Anode Prepared Using TiO <sub/>2</sub> ?Nanocrystals with Different Sizes for Enhanced Light-Trapping in Quantum Dots-Sensitized Solar Cells
摘要： Using TiO2 nanocrystals (NCs) with diameters of 20 nm (T20), 40 nm (T40) and 60 nm (T60) as starting materials, three TiO2 photo-anodes were constructed on FTO glass. Meanwhile, a triple-layered photo-anode was prepared by depositing the T20, the T40, and the T60 layer by layer on FTO glass (T60/T40/T20/FTO/glass). These four kinds of photo-anodes were sensitized with CdZn0.02S0.08Se0.92 QDs by successive ionic layer adsorption and reaction (SILAR). Based on these photo-anodes, four quantum dot-sensitized solar cells (QDSSCs) were ?nally obtained. The results indicated that the highest ef?ciency of 3.95% was obtained in the QDSSC with the triple-layered photo-anode. The short-circuit photocurrent density (Jsc) of the QDSSC with the triple-layered photo-anode was 1.25, 1.21 and 1.13-fold higher than that of the QDSSCs with T20-, T40- and T60-based photo-anode, respectively. Moreover, with the increase of the average size of the TiO2 NCs from 20 to 60 nm, the Jsc increased from 13.8 to 15.24 mA·cm?2. The optical properties, crystal structure and morphologies of the bare TiO2 ?lms and the CdZn0.02S0.08Se0.92 sensitized TiO2 photo-anodes were characterized by UV-Vis spectroscopy, XRD and SEM. The incident photon-to-electron conversion ef?ciency, the open circuit voltage decay and the electrochemical impedance spectroscopy of the QDSSCs were measured and discussed, so as to clarify the underlying mechanism of the property enhancement.
关键词： quantum dots-sensitized solar cells,TiO2 nanocrystals,light-trapping,CdZn0.02S0.08Se0.92 QDs,photo-anode
更新于2025-09-11 14:15:04
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Effects of alkylamine chain length on perovskite nanocrystals after washing and perovskite light-emitting diodes
摘要： Organic-inorganic hybrid lead halide perovskite nanocrystals (PeNCs) have great attention as a light source for perovskite light-emitting diodes (PeLEDs) owing to the superior optical properties. However, PeNCs typically use octylamine (OAm) as capping ligands which have insulating properties. Exploring a desirable short-alkylamine instead of OAm is required for the improvement of PeLEDs. Here, as a one of the strategies to solve this issue, the effects of alkylamine chain length for optical properties of PeNCs and PeLED characteristics are investigated. Pentylamine is an optimal short-alkylamine and precipitate luminescent PeNCs with high PLQY values of 90%. Importantly, pentylamine maintains a relatively high PLQY of 48% after spin-coating, due to the durability pentylamine has to ethyl acetate as a washing solvent. PeNCs capped with pentylamine also demonstrate an external quantum efficiency of over 1% with luminance of over 2000 cd/cm2, indicating that pentylamine has the potential to overcome the insulator properties of PeNC thin film.
关键词： optical properties,light-emitting diodes,perovskite nanocrystals,washing process,alkylamine chain length
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - A Novel Saturable Absorber: Transparent Glass-Ceramics Based on Co <sup>2+</sup> :Li(Al,Ga) <sub/>5</sub> O <sub/>8</sub> Spinel Nanocrystals
摘要： Cobalt ions (Co2+) embedded in tetrahedral (Td) sites are known for their intense absorption around 1.5 μm. Crystals such as spinel, MgAl2O4, doped with Co2+ ions in Td sites are recognized as excellent saturable absorbers (SAs) for eye-safe erbium lasers. Due to the relative difficulty to grow high-quality Co:MgAl2O4 crystals and fixed position of the Co2+ absorption band in spinel single-crystals, other Co2+-doped materials were proposed such as transparent glass-ceramics (GCs) and ceramics based on various spinels [1]. Transparent GCs offer a size-scalable synthesis method based on glass melting technology and variable spectroscopic properties as compared to crystals, and much higher laser induced damage threshold (LIDT) as compared to ceramics. GCs based on MgAl2O4 spinel nanocrystals modified by the addition of Ga3+ cations allow one to extend the SA properties until 1.7 μm [2]. In the present work, we describe the synthesis, structure, optical spectroscopy, nonlinear properties and passive Q-switching (PQS) performance of novel transparent GCs based on Co2+:Li(Al,Ga)5O8 nanocrystals. A lithium gallium aluminosilicate glass nucleated by TiO2 was doped with 0.1 mol% CoO. The GCs were produced by secondary heat-treatments at 680-850 oC for 6 h resulting in highly transparent, blue-colored samples, Fig. 1(a). The precipitation of nanosized spinel crystals was confirmed by XRD and TEM, Fig. 1(b,c), and Raman spectroscopy. The transparent GCs exhibited a broadband absorption band at 1.3-1.65 μm due to the 4A2(4F) → 4T1(4F) transition of Co2+ ions in Td sites in Li(Al,Ga)5O8 nanocrystals, Fig. 2(a). The saturable absoption of GC heat-treated at 750 oC for 6 h was studied by Z-scan method at 1540 nm using ns pulses. The saturation fluence FS is 0.50±0.05 J/cm2 and the LIDT exceeded 20 J/cm2, Fig. 2(b). This transparent GC was used to fabricate a SA for PQS of a compact diode-pumped Er,Yb:glass laser. This laser generated stable 7.4 ns / 1.34 mJ pulses at 1535 nm (peak power: 181 kW). The developed GC are promising as SAs for erbium lasers based on glass and crystalline materials (e.g., Er:YAG lasers emitting at 1617 nm and 1645 nm). This is because the broadband absorption of Co2+ ions in GCs is notably red-shifted as compared to Co:MgAl2O4 crystals which, in turn, is caused by the different spinel nanophase composition.
关键词： transparent glass-ceramics,Ga)5O8,Co2+:Li(Al,spinel nanocrystals,passive Q-switching,saturable absorber
更新于2025-09-11 14:15:04
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Nanocomposite material that protects against laser attack
摘要： An international group of researchers has produced a new biologically based optical-nanocomposite material that helps protect against strong light. The material, which consists of biologically generated elemental tellurium nanocrystals as well as a polymer, could protect electronic devices from attack by high-intensity bursts of light, such as emitted by common lasers aimed at aircraft, drones, surveillance cameras and other equipment, and could also find applications in improving the capacity of high-speed optical networking.
关键词： Nanocomposite material,tellurium nanocrystals,laser attack protection,high-speed optical networking,biologically generated
更新于2025-09-11 14:15:04
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Orientational Disorder in Epitaxially Connected Quantum Dot Solids
摘要： Periodic arrays of strongly coupled colloidal quantum dots (QDs) may enable unprecedented control of electronic bandstructure through manipulation of QD size, shape, composition, spacing, and assembly geometry. This includes the possibilities of precisely engineered bandgaps and charge carrier mobilities, as well as remarkable behaviors such as metal-insulator transitions, massless carriers, and topological states. However, experimental realization of these theoretically predicted electronic structures is presently limited by structural disorder. Here, we use aberration-corrected scanning transmission electron microscopy to precisely quantify the orientational disorder of epitaxially connected QD films. In spite of coherent atomic connectivity between nearest neighbor QDs, we find misalignment persists with a standard deviation of 1.9 degrees, resulting in significant bending strain localized to the adjoining necks. We observe and quantify a range of out-of-plane particle orientations over thousands of QDs, and correlate the in-plane and out-of-plane misalignments, finding QDs misoriented out-of-plane display a statistically greater misalignment with respect to their in-plane neighbors as well. Using the bond orientational order metric ψ4, we characterize both the fourfold symmetry and introduce a quantification of the local superlattice (SL) orientation. This enables direct comparison between local orientational order in the SL and atomic lattice (AL). We find significantly larger variations in the SL orientation, and a statistically robust but locally highly variable correlation between the orientations of the two differently scaled lattices. Distinct AL and SL behaviors are observed about a grain boundary, with a sharp boundary in the AL orientations, but a more smooth transition in the SL, facilitated by lattice deformation between the neighboring grains. Coupling between the AL and SL is a fundamental driver of film growth, and these results suggest nontrivial underlying mechanics, implying that simplified models of epitaxial attachment may be insufficient to understand QDs growth and disorder when oriented attachment and superlattice growth occur in concert.
关键词： orientational disorder,quantum dot solids,self-assembly,scanning transmission electron microscopy,nanocrystals,PbSe
更新于2025-09-11 14:15:04
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New strategies for colloidal-quantum-dot-based intermediate-band solar cells
摘要： The intermediate-band solar cell (IBSC) concept promises to increase the efficiency limit in a single-junction solar cell through the absorption of below-bandgap-energy photons. Despite their operating principle having been proposed over 20 years ago, IBSCs have not delivered on this promise yet, and the devices fabricated so far, mainly based on embedded epitaxial quantum dots, have instead operated with lower efficiency than conventional solar cells. A new paradigm, based on the exploitation as the intermediate band of the intragap states naturally occurring in the density functional theory description of colloidal (i.e., chemically synthesized) quantum dots, was suggested recently. Here, we revisit this intriguing concept unveiling its shortcomings and propose two alternative schemes: in the first, the localized electron surface trap states, ubiquitously found in commonly synthesized colloidal quantum dots, are used as intermediate bands in strongly coupled films made of small InAs nanocrystals and, in the second scheme, the intermediate band is provided by the conduction-band-minimum-derived miniband in films of larger InAs nanocrystals. Both schemes yield estimated limiting IBSC efficiencies exceeding Shockley-Queisser’s limit for a single absorber.
关键词： efficiency,InAs nanocrystals,intermediate-band solar cell,colloidal quantum dots,Shockley-Queisser limit
更新于2025-09-11 14:15:04
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Stability of Sn based inorganic perovskite quantum dots
摘要： Metal halide perovskite crystal structures have emerged as a class of optoelectronic materials, which combine the ease of solution processability with excellent optical absorption and emission qualities. However, the most promising perovskite structures rely on lead as a cationic species, thereby hindering commercial application. The replacement of lead with non-toxic alternatives such as tin has been studied in bulk but not in nanocrystals. In this work, we synthesize Sn and Pb based alloy perovskite nanocrystals by direct synthesis method by of taking mixture of Pb and Sn precursors in the desired ratio leading to quantum dots (QDs) of CsPb1-xSnxBryI3-y with successful Sn incorporation into the host lattice. As colloidal stability of these QDs is a crucial factor for device applications, we have studied the stability of the QDs under different conditions for these Sn based QDs and have found them to degrade faster upon using anti-solvents during washing process. In order to stabilize them, we have devised a purification method that is also discussed. Further, even though the optical and crystal structure stability in some of the inorganic perovskites leaves much room for improvement, so far there has been no studies on the structure property correlation. Here we study their structural purity and their optical stability after understanding the structure property correlation in CsPbI3 and CsPbBr3 perovskite structures. The stability of Sn doped perovskites obtained from a logical understanding of structure property correlations is found to be extremely stable across the series of compounds for upto three months.
关键词： Colloidal synthesis,Sn based perovskite nanocrystals
更新于2025-09-11 14:15:04
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Microwave-Assisted Synthesis of High-Energy Faceted TiO2 Nanocrystals Derived from Exfoliated Porous Metatitanic Acid Nanosheets with Improved Photocatalytic and Photovoltaic Performance
摘要： A facile one-pot microwave-assisted hydrothermal synthesis of rutile TiO2 quadrangular prisms with dominant {110} facets, anatase TiO2 nanorods and square nanoprisms with co-exposed {101}/[111] facets, anatase TiO2 nanorhombuses with co-exposed {101}/{010} facets, and anatase TiO2 nanospindles with dominant {010} facets were reported through the use of exfoliated porous metatitanic acid nanosheets as a precursor. The nanostructures and the formation reaction mechanism of the obtained rutile and anatase TiO2 nanocrystals from the delaminated nanosheets were investigated. The transformation from the exfoliated metatitanic nanosheets with distorted hexagonal cavities to TiO2 nanocrystals involved a dissolution reaction of the nanosheets, nucleation of the primary [TiO6]8? monomers, and the growth of rutile-type and anatase-type TiO2 nuclei during the microwave-assisted hydrothermal reaction. In addition, the photocatalytic activities of the as-prepared anatase nanocrystals were evaluated through the photocatalytic degradation of typical carcinogenic and mutagenic methyl orange (MO) under UV-light irradiation at a normal temperature and pressure. Furthermore, the dye-sensitized solar cell (DSSC) performance of the synthesized anatase TiO2 nanocrystals with various morphologies and crystal facets was also characterized. The {101}/[111]-faceted pH2.5-T175 nanocrystal showed the highest photocatalytic and photovoltaic performance compared to the other TiO2 samples, which could be attributed mainly to its minimum particle size and maximum specific surface area.
关键词： high-energy facets,photocatalytic activity,photovoltaic performance,anatase TiO2 nanocrystals
更新于2025-09-11 14:15:04