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Ag nanocrystals with nearly ideal optical quality: synthesis, growth mechanism, and characterizations
摘要： Though Ag nanocrystals are predicted as the best material for localized surface plasmon resonances (LSPR) in the visible light region, realization of their ideal LSPR properties is hindered by the stringent requirement, i.e., simultaneous control of their size, shape, crystallinity, and surface structure. To achieve this goal, a synthetic scheme in non-polar solvent coupled with mild oxidative-etching by H+ ions is established. With a trace amount of Cl- ions as catalysts, H+ ions (in the form of carboxylic acids) become active for selectively etching the nuclei (and small nanocrystals) with imperfect crystal structure, which results in a new growth mechanism for formation of monodisperse nanocrystals, namely “self-focusing of size/crystallinity distribution”. H+ ions, ligands, and other reagents in the scheme are confirmed to possess negligible effects on the surface dielectric properties of Ag nanocrystals. To eliminate radiative damping of LSPR, single-crystalline and monodisperse spherical Ag nanocrystals in the size range between 7 and 20 nm are synthesized using this one-pot scheme. With excellent control of all the structural parameters, the full-width-at-half-maximum of LSPR spectra of single-crystalline Ag nanocrystals match theoretical predictions in the entire size range, and the maximum quality factor (~20) of LSPR predicted by theory is realized. Raman enhancement factor of the single-crystalline Ag nanocrystals for crystal violet (excitation at 514 nm) is 5 times higher than that of the typical multi-twinned ones with the same size.
关键词： localized surface plasmon resonances,oxidative-etching,monodisperse,single-crystalline,Ag nanocrystals,Raman enhancement
更新于2025-09-23 15:21:21
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Photoluminescence Flickering and Blinking of Single CsPbBr <sub/>3</sub> Perovskite Nanocrystals: Revealing Explicit Carrier Recombination Dynamics
摘要： In order to obtain an in-depth understanding of the dynamics and mechanism of carrier recombination in CsPbBr3 nanocrystals (NCs), we have investigated the photoluminescence (PL) of this material at the single particle level using time-tagged-time-resolved method. The study reveals two distinct types of PL fluctuations of the NCs, which are assigned to flickering and blinking. The flickering is found to be due to excess surface trap on the NCs and the flickering single particles are transformed into blinking ones with significant enhancement of PL intensity and stability on post-synthetic surface treatment. Intensity correlated lifetime analysis of the PL time-trace reveals both trap-mediated nonradiative band edge carrier recombination and positive trion recombination in single NCs. Dynamical and statistical analysis suggests a diffusive nature of the trap states to be responsible for the PL intermittency of the system. These findings throw light on the nature of the trap states, reveal the manifestation of these trap states in PL fluctuation and provide an effective way to control the dynamics of CsPbBr3 NCs.
关键词： CsPbBr3,Surface Treatment,Carrier Recombination,Photoluminescence,Nanocrystals
更新于2025-09-23 15:21:21
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Single Nanocrystal Spectroscopy of Shortwave Infrared Emitters
摘要： Short-wave infrared (SWIR) emitters are at the center of ground-breaking applications in biomedical imaging, next-generation optoelectronic devices, and optical communications. Colloidal nanocrystals based on indium arsenide are some of the most promising SWIR emitters to date. However, the lack of single-particle spectroscopic methods accessible in the SWIR has prevented advances in both nanocrystal synthesis and fundamental characterization of emitters. Here, we demonstrate an implementation of a solution photon correlation Fourier spectroscopy (s-PCFS) experiment utilizing the SWIR sensitivity and time resolution of superconducting nanowire single-photon detectors to extract indium arsenide/cadmium selenide (InAs/CdSe) core/shell single-particle emission linewidths from colloidal nanocrystals emissive from 1.2 to 1.6 μm. We show that the average single InAs/CdSe nanocrystal ?uorescence linewidth is, remarkably, as narrow as 52 meV, similar to what has been observed in some of the most narrowband nanostructured emitters in the visible region. Additionally, the single nanocrystal ?uorescence linewidth increases with increasing shell thickness, suggesting exciton?phonon coupling as the dominant emission line-broadening mechanism in this system. The development of the SWIR s-PCFS technique has enabled measurements of spectral linewidths of colloidal SWIR-emissive NCs in solution and provides a platform to study the single NC spectral characteristics of SWIR emitters.
关键词： nanocrystals,single-molecule spectroscopy,core/shell,indium arsenide,short-wave infrared
更新于2025-09-23 15:21:21
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Phase transformation and photoluminescence of undoped and Eu3+-doped zinc stannate (Zn2SnO4) nanocrystals synthesized by hydrothermal method
摘要： In this work we report a hydrothermal approach for synthesis of zinc stannate (Zn2SnO4–ZTO) nanocrystals. Structural properties and morphology of the samples were investigated in detail. In particular, our research focused on the effect of hydrothermal duration on the phase composition of ZTO nanocrystals. By combining X-ray diffraction analysis, scanning electron microscopy and selected area energy-dispersive X-ray spectroscopy, a crystalline phase transformation during the hydrothermal process was enlightened. The ZTO nanocrystals were doped with europium ions. The room-temperature emission spectra of the undoped ZTO and Eu3+-doped ZTO nanocrystals were recorded. The emission spectra of the undoped ZTO nanocrystals showed two broad bands related to the lattice defects, while the spectra of Eu3+-doped ZTO nanocrystals exhibited the narrow emission peaks, which were assigned to the radiative intra-configurational f–f transitions of Eu3+ ions.
关键词： nanocrystals,europium doping,hydrothermal method,photoluminescence,zinc stannate
更新于2025-09-23 15:21:21
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Colloidal CdSe Nanocrystals as a Material for Optoelectronics and Biomedical Imaging
摘要： Cadmium selenide nanocrystals were prepared in water phase chemistry technique with gelatin, polivinil alcohol, lactose, triton-100 acting as capping agent. Structures were characterized using scanning electron microscopy (SEM), visible absorption and photoluminescence spectroscopies. Influence of component concentrations and technological parameters on nanocrystals average size and properties was studied
关键词： photoluminescence,optical,selenide,optoelectronics,biomedical imaging,cadmium,nanocrystals,absorption
更新于2025-09-23 15:21:21
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Synthesis and Photophysical Properties of Multichromic Nanocrystals of Polymethine Dyes
摘要： A unique method for the self-assembly of multilayer multichromic molecular crystals from three various polymethine dyes absorbing light in the broad spectral range has been developed. This method is based on the formation of an anionic platform of J-aggregates of magnesium complexes of thiamonomethinecyanines in an aqueous solution followed by the matrix synthesis of J-aggregates of two cationic trimethinecyanines on the surface of the platform. Spectral, luminescent, and photoelectric properties of the multichromic crystals of dyes have been studied. It has been shown that each multichromic organic crystal is a multilayer photoelement which possesses photoconductivity in three maxima of exciton absorption in the blue, green, and red spectral ranges with efficiency from 2.7 to 6.1%. The results form the basis for the technological development of high-organized molecular structures possessing unique optical and photoelectric properties with the aim of applying them in organic and hybrid organic/inorganic photonics and optoelectronics, including in the form of thin-film photoconverters in broad spectral ranges.
关键词： multichromic nanocrystals,polymethine dyes,nanophotonics,photoelectric properties,J-aggregates
更新于2025-09-23 15:21:21
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Observation of Optical Band-Gap Narrowing and Enhanced Magnetic Moment in Co-Doped Sol–Gel-Derived Anatase TiO <sub/>2</sub> Nanocrystals
摘要： The magnetic behavior of TiO2 and doped TiO2 nanocrystals has been a challenge due to the unambiguous nature of defects present in oxide semiconductors. Here, a simple, low-temperature sol?gel method is developed for the synthesis of low-dimensional and highly efficient stable anatase TiO2 nanocrystals. The X-ray powder diffraction pattern and Raman spectra confirm the formation of a single-phase anatase structure of TiO2. High-resolution transmission electron microscopy studies reveal the crystalline nature of the sol?gel-derived nanocrystals. The increase in lattice parameters together with the shifting and broadening of the most intense Eg(1) mode in micro-Raman spectra of Co-doped TiO2 nanocrystals indicate the incorporation of Co in TiO2. Shifting of the absorption edge to the visible region in UV?visible spectra indicates narrowing of the band gap due to Co incorporation in TiO2. X-ray photoelectron spectra confirm the presence of Co2+ and Co3+ in Co-doped TiO2 samples. Oxygen vacancy defects lead to the formation of bound magnetic polarons which induces a weak ferromagnetic behavior in air-annealed 3% Co-doped TiO2 at room temperature. It is observed that irrespective of the dopant ion, whether magnetic or nonmagnetic, the overlapping of bound magnetic polarons alone can induce ferromagnetism, while the magnetic impurities give rise to an enhanced paramagnetic moment for higher Co concentrations. A detailed understanding on the variation of these magnetic properties by estimating the concentration of bound magnetic polarons is presented, which is in corroboration with the photoluminescence studies. The observed band-gap narrowing in Co-doped TiO2 nanostructures and the mechanism underlying the magnetic interactions associated with the magnetic impurity concentration are advantageous from an applied perspective, especially in the field of spintronic and magneto-optic devices.
关键词： spintronic,magnetic moment,nanocrystals,optical band-gap narrowing,TiO2,magneto-optic devices,Co-doped,sol?gel
更新于2025-09-23 15:21:21
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Long Exciton Dephasing Time and Coherent Phonon Coupling in CsPbBr <sub/>2</sub> Cl Perovskite Nanocrystals
摘要： Fully-inorganic cesium lead halide perovskite nanocrystals (NCs) have shown to exhibit outstanding optical properties such as wide spectral tunability, high quantum yield, high oscillator strength as well as blinking-free single photon emission and low spectral diffusion. Here, we report measurements of the coherent and incoherent exciton dynamics on the 100 fs to 10 ns timescale, determining dephasing and density decay rates in these NCs. The experiments are performed on CsPbBr2Cl NCs using transient resonant three-pulse four-wave mixing (FWM) in heterodyne detection at temperatures ranging from 5 K to 50 K. We found a low-temperature exciton dephasing time of 24.5±1.0 ps, inferred from the decay of the photon-echo amplitude at 5 K, corresponding to a homogeneous linewidth (FWHM) of 54±5 μeV. Furthermore, oscillations in the photon-echo signal on a picosecond timescale are observed and attributed to coherent coupling of the exciton to a quantized phonon mode with 3.45 meV energy.
关键词： quantum dots,coherence,four wave mixing,nanocrystals,heterodyne detection,Perovskite,T2,lead halide,photon echo,phonons
更新于2025-09-23 15:21:21
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Electron–hole correlations govern Auger recombination in nanostructures
摘要： The fast nonradiative decay of multiexcitonic states via Auger recombination is a fundamental process affecting a variety of applications based on semiconductor nanostructures. From a theoretical perspective, the description of Auger recombination in confined semiconductor nanostructures is a challenging task due to the large number of valance electrons and exponentially growing number of excited excitonic and biexcitonic states that are coupled by the Coulomb interaction. These challenges have restricted the treatment of Auger recombination to simple, noninteracting electron–hole models. Herein we present a novel approach for calculating Auger recombination lifetimes in confined nanostructures having thousands to tens of thousands of electrons, explicitly including electron–hole interactions. We demonstrate that the inclusion of electron–hole correlations are imperative to capture the correct scaling of the Auger recombination lifetime with the size and shape of the nanostructure. In addition, correlation effects are required to obtain quantitatively accurate lifetimes even for systems smaller than the exciton Bohr radius. Neglecting such correlations can result in lifetimes that are 2 orders of magnitude too long. We establish the utility of the new approach for CdSe quantum dots of varying sizes and for CdSe nanorods of varying diameters and lengths. Our new approach is the first theoretical method to postdict the experimentally known “universal volume scaling law” for quantum dots and makes novel predictions for the scaling of the Auger recombination lifetimes in nanorods.
关键词： semiconductor nanocrystals,quantum dots,excitons,auger recombination,biexcitons,nanorods
更新于2025-09-23 15:21:21
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Interface Engineering of CsPbBr <sub/>3</sub> Nanocrystal Light-Emitting Diodes via Atomic Layer Deposition
摘要： Perovskite nanocrystal (PNC) suffers from solution corrosion and water/oxygen oxidation when used in light-emitting diodes (LEDs). Atomic layer deposition (ALD) is applied to introduce Al2O3 infilling and interface engineering for the CsPbBr3 nanocrystal emission layers, and the inorganic electron transport layer-based CsPbBr3–ZnMgO LED device is fabricated. The introduction of Al2O3 ALD layers significantly improves the tolerance of CsPbBr3 PNC thin films to polar solvents ethanol of ZnMgO during spin coating. The operation lifetime of ALD-treated CsPbBr3 PNC–ZnMgO LED is prolonged to about two orders of magnitude greater than that of the CsPbBr3 PNC-TPBi LED device with a largely improved external quantum efficiency (EQE) value. Moreover, the infilling of Al2O3 into the CsPbBr3 layer boosts the carrier mobility for more than 40 times inside the light-emission layer. However, the interfacial carrier transport between different functional layers is hindered by the insulated Al2O3 layer, which provides an effective barrier for excess electron transport. Such a favorable band alignment facilitates the carrier balance of the device and contributes to the improved electroluminescent performance of the device with ALD Al2O3 interface engineering, which is further supported by theoretical device modeling. Herein, a facile method is provided to fabricate PNC-LED devices with both high efficiency and long-term lifetime.
关键词： light emitting diodes,working stability,interface engineering,atomic layer deposition,CsPbBr3 perovskite nanocrystals
更新于2025-09-23 15:21:01