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Core/Shell Upconversion Nanocrystal Hybrids with Temperature-Dependent Emission Color Changes for Multilevel Anticounterfeiting Applications
摘要： This work presents a novel and highly secure anticounterfeiting strategy based on core/shell upconversion nanocrystal (UCNC) hybrids with temperature-responsive multicolor emissions. Opposite luminescent temperature-dependences are found for active-core@inert-shell (thermal quenching) and active-core@active-shell (thermally induced enhancement) UCNCs. Accordingly, their hybrids are designed to show obvious color changes with increasing temperature under 975 nm excitation. Various color-shifting pathways (from white to green, blue to green, etc.) are achieved by adjusting the core/shell NC combinations in the hybrids. Moreover, color changes of the printed patterns using the hybrid NC inks can be realized by the simple heating treatment, or by increasing the laser power and prolonging the irradiation time. The results indicate the great potential of these core/shell NC hybrids for anticounterfeiting applications with high-level security and convenient authentication methods.
关键词： upconversion,anticounterfeiting,nanocrystals,hybrids,luminescence
更新于2025-09-10 09:29:36
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Recent advances in the manipulation of circularly polarised light with cellulose nanocrystal films
摘要： Significant advances have been made to control the iridescence and the selective reflection of left circularly polarised (LCP) light, and transmission of right circularly polarised (RCP) light of solid films prepared from cellulose nanocrystals (CNCs). However the manipulation of the photonic properties of the CNCs films, which reflect both RCP and LCP light is less investigated. Solid films prepare from natural sources as CNCs have advantageous characteristics that are absent in other synthetic structures, such as wide availability and renewability. Here we review and compare recent research activity involving the production and characterization of photonic band gap structures resulting from an anisotropic layer inserted between two cholesteric layers with different helical pitches but the same handedness. We make connections between systems existing in Nature and synthetic ones with the hope of advancing in the production and manipulation of CNCs-based photonic structures.
关键词： Cellulose nanocrystals,Photonics,Circularly polarised light,Bio-inspired materials,Iridescence,Liquid crystals
更新于2025-09-10 09:29:36
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Local Structure Analysis of KNbO<sub>3</sub> Nanocrystals with Cubic Shape
摘要： KNbO3 nanocrystals were grown by solvothermal technique assisted by a microwave treatment. The morphology of nanocrystals is a cubic shape and the crystal structure is also cubic system. This is an ideal case for the so-called Sherrer's equation. We performed high-energy X-ray scattering to extract various structural parameters. The particle size can be evaluated by the Sherrer's equation. The unit cell size of the KNbO3 nanocrystals was reduced as the particle size increased. The local structure of the nanocrystals was found to be a rhombohedral structure similar to that of the bulk KNbO3. Although the periodic structure of the perovskite system unchanged locally, the first-nearest neighbor and the second-nearest neighbor bond distances corresponding to Nb-O and K-O was changed as the particle size increased.
关键词： nanocrystals,local structure,KNbO3,atomic pair-distribution function
更新于2025-09-10 09:29:36
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Functional properties of LaxCe1?xO2?δ nanocrystals and their bulk ceramics
摘要： Structure–property correlations were investigated for LaxCe1?xO2?δ (x = 0.05, 0.15) system (for both nanoparticles and ceramic). The nanoparticles were synthesized by the co-precipitation route and characterized for their structural, catalytic and visible light driven photocatalytic properties. Synthesised LaxCe1?xO2?δ nanopowders depicted phase purity with excellent compositional control as confirmed by various structural characterisation tools. The 15% La3+-doped ceria nanoparticles portrayed superior photocatalytic properties; complete degradation (99%) of the methylene blue dye was observed within 60 min of visible light irradiation under an alkaline medium. High density (> 96%) of the ceramics (sintered at 1580 °C for 2 h) confirmed promising sinterability of the synthesised powders. The ionic conductivities of the LaxCe1?xO2?δ ceramics increased with temperature and frequency owing to enhanced oxygen vacancies in the ceria matrix as a result of doping (of La3+-ions); a maximum conductivity of ~ 8.4 × 10?2 S cm?1 was obtained at 900 °C for the 15% La3+-doped ceria ceramics at 1 MHz frequency.
关键词： LaxCe1?xO2?δ,nanocrystals,photocatalytic properties,co-precipitation,ionic conductivity,bulk ceramics
更新于2025-09-10 09:29:36
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Comparative activity of aqueous dispersions of CdS nanocrystals stabilized by cationic and anionic polyelectrolytes in photocatalytic hydrogen production from water
摘要： The results of a study on the photocatalytic activity of aqueous dispersions of Ni-doped CdS nanocrystals (NCs) covered with an amphiphilic polyelectrolyte (PE) shell, i.e., a polycation (NC-PC) or polyanion (NC-PA), are presented for the first time. The H2 evolution rate measured under identical conditions served as a measure of activity. The NC-PC and NC-PA samples were characterized by similar PE content (~40%) and monomodal size distribution. According to our calculations based on the NC dimensions and lattice parameters, about one macromolecule of the PE is required to stabilize one NC. The average hydrodynamic diameter of the NC-PC was found to be 1.5 times larger than that of the NC-PA due to the difference between their chemical structures and different abilities of ionogenic groups to dissociate. The photocatalytic activity of the PE-stabilized CdS nanocrystals was significantly influenced by the type of the PE, while the H2 evolution rate depended on the reducing medium used during the process. When the medium contained Na2S or when the PE-stabilized NCs were pre-treated with Na2S, the effect of the shell type was more pronounced and the activity of NC-PA was 2 to 14 times higher than that of NC-PC.
关键词： polyelectrolytes,nanocrystals,photocatalysis,cadmium sulfide,hydrogen evolution reactions,nickel
更新于2025-09-10 09:29:36
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Broadband Defects Emission and Enhanced Ligand Raman Scattering in 0D Cs <sub/>3</sub> Bi <sub/>2</sub> I <sub/>9</sub> Colloidal Nanocrystals
摘要： Excitonic 0D and 2D lead-halide perovskites have been recently developed and investigated as new materials for light generation. Here broadband (>1 eV) emission from newly synthesized 0D lead-free colloidal Cs3Bi2I9 nanocrystals (NCs) is reported. The nature of their emissive states as well as the relative dynamics which are currently hotly debated are investigated. In particular, it is found that the broadband emission is made by the coexistence of emissive excitons and sub-bandgap emissive trap-states. Remarkably, evidence of enhanced Raman scattering from the ligands is observed when attached to the NCs surface, an effect that is preliminarily attributed to strong exciton-ligands electronic coupling in these systems.
关键词： trap-states emission,enhanced Raman scattering,broadband emission,lead-free perovskites,0D nanocrystals
更新于2025-09-10 09:29:36
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Telescoping synthesis and goldilocks of CZTS nanocrystals
摘要： Facile, low-temperature synthesis of kesterite CZTS nanocrystals (NCs) using single solvent by heating up approach is presented for the first time. Temperature and time dependence on the structural, morphological and compositional properties are investigated in detail. The size of the NCs was found to increase from 15 to 45 nm with increases in the reaction temperature. From the structural analysis, secondary and ternary phases were detected at less reaction time, and pure phase of CZTS was obtained at 3 h. On the basis of the detailed time-dependent phase evolution, a plausible formation mechanism of CZTS NCs was proposed. The sequence of CZTS phase evolved from Cu2S phase to Cu2SnS3 intermediate compound and finally to pure kesterite CZTS. The optimal composition of Cu/(Zn+Sn) and Zn/Sn ratio was obtained at 3 h. The calculated band gap was found to be 1.5 eV which is an optimum value for solar cell applications. Thus, the results revealed that the reaction temperature and time played a determining role to obtain pure phase CZTS with controlled composition and optimum bandgap.
关键词： Low-temperature,Heating up approach,Nanocrystals,CZTS
更新于2025-09-10 09:29:36
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Synthesis of ultra-narrow PbTe nanorods with extremely strong quantum confinement
摘要： Monodisperse, high-quality, ultra-narrow PbTe nanorods were synthesized for the first time in a one-pot, hot-injection reaction using trans-2-decenoic acid as the agents for lead precursors and tris(diethylamino)phosphine as the telluride precursors. High monomer reactivity, rapid nucleation and fast growth rate derived from the new precursors led to the anisotropic growth of PbTe nanocrystals at low reaction temperatures (< 150 oC). In addition, the aspect ratio of PbTe nanorods could be largely adjusted from 4 to 15 by tuning the Pb to Te precursor molar ratio and reaction temperatures. Moreover, the synthesized ultra-narrow PbTe nanorods exhibited extremely strong quantum confinement and presented unique optical properties. We revealed that the diameter and length of PbTe nanorods could significantly affect their optical properties, which potentially offer them new opportunities in the application of optoelectronic and thermoelectric devices and make them desired subjects for multiple exciton generation and other fundamental physics studies.
关键词： optical properties,PbTe nanorods,Colloidal semiconductor nanocrystals
更新于2025-09-10 09:29:36
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Disentangling the Electron and Hole Dynamics in Janus CdSe/PbSe Nanocrystals through Variable Pump Transient Absorption Spectroscopy
摘要： CdSe/PbSe Janus hetero-nanocrystals (HNCs) represent an interesting system where structurally immiscible CdSe and PbSe co-exist in a single structure with intermixed electronic states. Here, we have investigated the carrier dynamics in Janus CdSe/PbSe HNCs through ultrafast transient absorption spectroscopy by selectively exciting either the CdSe or the PbSe domains. Upon excitation of the CdSe domain sub-picosecond hole transfer to the hybrid interfacial PbSe states were identified. On the other hand, the transfer of hot electron from PbSe to CdSe was evident upon creation of hot electrons in PbSe domain without exciting the CdSe domain. The photo-excited hot hole also gets transferred to the hybrid interfacial states in sub-ps time (~1ps) bleaching the corresponding transition. The decay of the localized hole was found to be much slower compared to the electron which can be beneficial for carrier extraction and multiexciton generation. The finding of hot electron transfer in a single structure and slow decay of holes can thus prove to be advantageous for future design of photovoltaic devices.
关键词： carrier dynamics,ultrafast transient absorption spectroscopy,CdSe/PbSe Janus hetero-nanocrystals,photovoltaic devices,hot electron transfer
更新于2025-09-10 09:29:36
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Solvent-Assisted Tuning the Size and Shape of CsPbBr3 Nanocrystals via Re-Dispersion Process at Ambient Condition
摘要： All-inorganic CsPbBr3 perovskite nanocrystals are emerging as a new class of semiconductors with outstanding optoelectronic properties and great potential for various applications, such as, lasing, photon detection, photovoltaics etc. This article provides the effect of solvents on the re-precipitation of CsPbBr3 perovskite at room temperature. The results observed for CsPbBr3 perovskite in various anti-solvent showed various cubes (nano to micro size), self-assembly of nanocubes and nanorods. In addition, all the various size (nano to micro), self-assembly of nanocubes and shape-controlled nanorods exhibited band-gap tuning at the green light region. The corresponding microscopy (FE-SEM and HR-TEM) images and photoluminescence quantum yield as well as lifetime decay are presented. To the best of our literature knowledge this is the first report on various solvent assisted studies on CsPbBr3 perovskite nanocrystals.
关键词： CsPbBr3 Nanocrystals,nanocubes,effect of solvents,lifetime decay,nanorods,self-assembly
更新于2025-09-10 09:29:36