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Finite-size (d=5.4-112 nm) and surface effects on the structural, optical, and magnetic properties of ferrimagnetic inverse-spinel MnCo2O4 are reported. For d ≥ 87 nm, partial tetragonal distortion of the inverse spinel-lattice was observed. The Curie temperature TC of MnCo2O4 nanostructures, as determined by dc-magnetic susceptibility (χ) measurements, follows a finite-size scaling relation TC(d)=TC(1)[1-(ζ0/d)λ] with a shift exponent λ=0.75±0.15 and microscopic correlation length ζ0=1.4±0.3 nm, which is consistent with the mean field theory. For T>TC, χ(T) fits Néel's expression for the two-sublattice model with antiferromagnetic molecular field (exchange) constants NBB~85.16 (JBB~2.94×10-22 J), NAB~110.96 (JAB~1.91×10-22 J), and NAA~43.8 (JAA~1.13×10-22 J) and asymptotic Curie temperature Ta~717.63 K. The optical energy bandgap Eg, evaluated from the Kubelka-Munk function ([F(R∞)hω]2 =C2(hω - Eg)) is blueshifted to 2.4 eV (d~5.4 nm) from 1.73 eV (d~112 nm) due to the quantum confinement and nonstoichiometry. The role of tetragonal distortion and grain-size-effects in the intensity of crystal field transitions and variation in the magnetic ordering are further discussed and compared with Co3O4 nanostructures. [ABSTRACT FROM AUTHOR]

By contact of platinum catalyst with Si wafers immersed in H2O2 plus HF solutions, ultra-low reflectance Si surfaces can be produced. The ultra-low reflectance results from the formation of a nanocrystalline Si (nc-Si) layer with ~300 nm thickness. A porosity-graded optical model consisting of 19 sublayers for the nc-Si layer, which is determined from SEM and TEM observations, and the fitting of ellipsometric spectra, is found to well explain the optical properties. The dielectric function of each sublayer is calculated from the Bruggeman effective medium approximation using porosity and the dielectric functions of Si and ~5 nm Si nanocrystals. The reflectance calculated from the optical model shows a good agreement with the experimental result in the wide wavelength region between 300 and 800 nm. This good agreement demonstrates that the ultra-low reflectance of the nc-Si/Si structure results from the refractive index monotonically increasing with the depth. [ABSTRACT FROM AUTHOR]

Microstructure in polycrystalline materials is composed of grain boundary plane, triple junction line, and vertex point. They are the integral parts of the grain boundary network structure and the foundation for the structure-property relations. In polycrystalline, especially nanocrystalline, materials, it becomes increasingly difficult to probe the atomistic structure of the microstructure components directly in experiment due to the size limitation. Here, we present a numerical approach using pair correlation function from atomistic simulation to obtain the detailed information for atomic order and disorder in the grain boundary network in nanocrystalline materials. We show that the atomic structures in the different microstructural components are related closely to their geometric size and shape, leading to unique signatures for atomic structure in microstructural characterization at nanoscales. The dependence varies systematically with the characteristic dimension of the microstructural component: liquid-like disorder is found in vertex points, but a certain order persists in triple junctions and grain boundaries along the extended dimensions of these microstructure components. [ABSTRACT FROM AUTHOR]

In this study, complete solid state amorphization in nanocrystalline nickel has been achieved through cryogenic laser shock peening (CLSP). High resolution transmission electron microscopy has revealed the complete amorphous structure of the sample after CLSP processing. A molecular dynamic model has been used to investigate material behavior during the shock loading and the effects of nanoscale grain boundaries on the amorphization process. It has been found that the initial nanoscale grain boundaries increase the initial Gibbs free energy before plastic deformation and also serve as dislocation emission sources during plastic deformation to contribute to defect density increase, leading to the amorphization of pure nanocrystalline nickel. [ABSTRACT FROM AUTHOR]

Silicon nanocrystals have been generated by laser induced phase separation in SiOx films. A continuous wave laser emitting at 405 nm is focused to a 6 µm diameter spot on 530 nm thick SiOx films deposited on fused silica substrates. Irradiation of lines is accomplished by focus scanning. The samples are investigated by atomic force microscopy, TEM, Raman spectroscopy, and photoluminescence measurements. At a laser power of 35 mW corresponding to an irradiance of about 1.2 × 105W/cm2, the formation of Si-nanocrystals in the film without any deterioration of the surface is observed. At higher laser power, the central irradiated region is oxidized to SiO2 and exhibits some porous character, while the surface remains optically smooth, and nanocrystals are observed beside and beneath this oxidized region. Amorphous Si-nanoclusters are formed at lower laser power and around the lines written at high power. [ABSTRACT FROM AUTHOR]

We report a controlled emission of Ce3+ ions inside single Yttrium Aluminum Garnet Y3Al5O12 (YAG:Ce3+) nanocrystals with a diameter of 22±10 nm as a result of a coupling of a surface plasmon mode propagating along single gold nanowire (NW). From the photoluminescence images, the intensity for single YAG:Ce3+ nanocrystals in the proximity of the single gold NW increases by a factor of two in comparison with that without the NW. Also, we observe a maximum of 3.8-fold emission rate enhancements for the single nanocrystal close to the single gold NW. The emission rate enhancements of YAG:Ce3+ nanocrystals are two folds the enhancements of 100-nm fluorescent nanospheres. This value is in agreement with the calculation of a combination from the analytical scattering model and boundary element method. We also confirm that the small size light sources are more efficient for the emission rate enhancements. Thus, the controlled emission of small YAG:Ce3+ nanocrystals with the perfect photostabilities will pave the way for the ultimate efficient nanoscale light sources. [ABSTRACT FROM AUTHOR]

We use molecular simulation to construct equilibrium phase diagrams for two recently introduced model materials with isotropic, soft-repulsive pair interactions designed to favor diamond and simple cubic lattice ground states, respectively, over a wide range of densities [Jain et al., Soft Matter 9, 3866 (2013)]. We employ free energy based Monte Carlo simulation techniques to precisely trace the inter-crystal and fluid-crystal coexistence curves. We find that both model materials display rich polymorphic phase behavior featuring stable crystals corresponding to the target ground-state structures, as well as a variety of other crystalline (e.g., hexagonal and body-centered cubic) phases and multiple reentrant melting transitions. [ABSTRACT FROM AUTHOR]

Nanocrystal superlattices are materials formed by assembly of monodisperse nanocrystal building blocks that are tunable in composition, size, shape, and surface functionalization. Such materials offer the potential to realize unprecedented combinations of physical properties, but theoretical prediction of such properties, particularly elastic properties, remains a challenge. Here we report the Young's moduli, bulk moduli, and Poisson's ratios of CdSe nanocrystal superlattices computed from fully atomistic molecular dynamics simulations, coarse grained models, and effective medium theory. The atomistic simulations yield Young's moduli in the 4-5 GPa range, in agreement with previously reported results for similar nanocrystal superlattice systems. A clear increase of Young's modulus and bulk modulus with increasing nanocrystal core size is observed, while Poisson's ratio decreases slightly with core size. Effective medium theory overpredicts the moduli, and it is surmised that this arises from its neglect of the atomic-level details of the of the core-ligand interface. The coarse grained calculations, using existing nanocrystal interaction models from the literature, also show similar increases with core size but predict moduli that are two orders of magnitude lower than the present atomistic results and previous literature. It is concluded that coarse grained models, in their current form, are not appropriate for calculating elastic properties of nanocrystal superlattices and that fully atomistic models are better suited for this purpose. [ABSTRACT FROM AUTHOR]

The Raman spectra of SiO2 films containing InSb spherical nanocrystals produced by ion-beam synthesis are studied. TO- and LO-like modes in the spectra of the InSb nanocrystals are detected at frequencies of 187 and 195 cm–1, respectively. The shift of these modes to high frequencies with respect to the corresponding frequencies in InSb bulk crystals is analyzed from the viewpoint of the influence of the quantum-confinement effect, strains in nanocrystals, the surface phonon frequency, and scattering at the frequency corresponding to stretched anion–cation modes at the surface of polar spherical nanocrystals. The position of the 195-cm–1 mode corresponds to LO phonons in InSb nanocrystals hydrostatically compressed in the SiO2 matrix at pressures of about 10 kbar. The 187-cm–1 mode corresponds to resonance at the Fröhlich frequency. [ABSTRACT FROM AUTHOR]

In this paper, we characterize and optimize design of a candidate ultraviolet photodiode based on nitrogen-doped ultrananocrystalline diamond hydrogenated amorphous carbon (UNCD/a-C:H) composite films grown on crystalline-Si substrates by coaxial arc plasma deposition. A comprehensive study including growth, fabrication, characterization, and modeling of the photodetector is presented here. The current-voltage characteristics of the device were reproduced and their critical parameters were extracted from a good matching between experimental and simulation results. A midgap acceptor-like defect state density of ~ 5 × 10 17 cm −3 eV −1 was found to be the dominant defect in the UNCD/a-C:H film, in addition to an interface defect density of ~ 3 × 10 13 cm −2 eV −1 at the interface of the UNCD/a-C:H film and the Si substrate. Experimental and simulation results showed that introducing an intrinsic UNCD/a-C:H layer in a pin heterostructure would significantly reduce the device leakage current and consequently improve its performance as an ultraviolet photodiode. Unoptimized fabricated devices exhibited a room temperature photoresponsivity of 135 mA/W measured under illumination of ultraviolet monochromatic light with a wavelength of 254 nm. The key parameters for optimized design of the device were extracted and investigated in details. [ABSTRACT FROM AUTHOR]

Abstract The reinforcing effects of native and modified cellulose nanocrystal (CNC) materials on thermosetting epoxies are investigated. CNC modification is conducted by grafting an activated medium chain fatty acid to substitute the hydroxyl functional group. The level and effect of CNC modification are evaluated using Fourier Transform Infrared (FTIR), elemental analysis (EA), thermal analysis, contact angle measurements, and solvent dispersibility studies. The EA shows that CNCs with a degree of substitution (DS) of 0.2, 0.8 and 2.4 is obtained depending on the concentration of the catalyst and reactant used in the process. The native and modified CNCs are then incorporated into epoxy resin via an in situ polymerization. Dynamic mechanical analysis, and stress – strain studies showed that the lightly modified CNCs (DS 0.2 and DS 0.8) have an impressive reinforcing effect. CNC with DS 0.2 at 5% loading resulted in a 77% and 44% improvement in the tensile strength and modulus of the baseline epoxy matrix, respectively indicating significant reinforcement. Such materials can be useful in structural composites, printed circuit boards, and adhesive applications. An improvement in the dispersion and an enhanced interfacial adhesion between the modified CNC and the epoxy matrix is proposed for the observed reinforcement. A higher degree of fatty acid grafting onto the CNC resulted in a hydrophobic material, which reduced the water uptake of the epoxy nanocomposites. Graphical abstract Image Highlights • Heterogeneous esterification of CNC with an activated fatty acid induced hydrophobicity of CNCs. • The crystallinity, dispersability, and thermal stability of CNCs was altered with the modification. • Lightly modified CNC resulted in excellent reinforcement of epoxy resins. • Water absorption of epoxy nanocomposites diminished with the hydrophobic CNC. [ABSTRACT FROM AUTHOR]

The nano-crystalline SnS 2 layer thin film was fabricated on a fluorinated tin oxide (FTO) glass substrate by a chemical bath deposition method. The structural characteristics of the SnS 2 /FTO thin film were investigated by using scanning electron microscope and atomic force microscope. The Raman spectroscopy indicated that the SnS 2 /FTO thin film was successfully grown on the FTO glass substrate. The nonlinear absorption properties of the SnS 2 /FTO thin film were investigated using an open-aperture Z-scan technique. The experimental results show that the SnS 2 /FTO thin film exhibits a saturable absorption. Consequently, the SnS 2 /FTO thin film has great potential applications in optical devices such as mode-locked or Q-switched lasers. [ABSTRACT FROM AUTHOR]

Au@Sn2S3 and Au@SnS2 core–shell hybrid nanocrystals (HNCs) were respectively accessed via an aqueous cation exchange-mediated growth strategy by using different phosphine ligands. The choice of proper ligands during synthesis is imperative to optimize the photoelectrochemical performance of these previously hardly accessible HNCs that manifest compelling plasmon–exciton interactions. [ABSTRACT FROM AUTHOR]

PbS nanocrystals are an important narrow-gap material for solar cells and photodetectors. Nevertheless, their application may be limited because device performance can be affected by atmospheric conditions. Indeed, the presence of oxygen and/or water can degrade the active layers, possibly leading to device failure. Strategies to address this issue are therefore actively explored. Here we report a solution-processed PbS quantum dot solar cell, consisting of a PbS-silane functionalized reduced graphene oxide (PbS-rGO) layer on top of the PbS absorber film, which enhances device stability, especially when the solar cells are exposed to moisture. Power conversion efficiency (PCE) measurements demonstrate a slower degradation under continuous illumination for solar cells with PbS-rGO. When storing the samples under saturated water vapor, differences are even more remarkable: with PbS-rGO the solar cells essentially maintain their initial PCE, while the PCE of the PbS reference devices is reduced by 50% after 5 days. Scanning electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy reveal the damage to the PbS films and the formation of PbSO x crystals in the PbS reference devices. Such crystals are not observed in the PbS-rGO devices, further supporting the importance of the PbS-rGO barrier layer. [ABSTRACT FROM AUTHOR]

A novel modified polyvinylidene fluoride (PVDF) membranes with adding α-Fe 2 O 3 nanocrystals were prepared for the photocatalytic degradation of organic contaminants. The α-Fe 2 O 3 nanocrystals entrapped PVDF membranes were characterized by XRD, SEM and TEM. The photocatalytic performance and antifouling property were studied by filtration and degradation of Congo red (CR) under visible light irradiation. The results show that the photocatalytic activity of the α-Fe 2 O 3 /PVDF membranes were significantly influenced by the morphology of α-Fe 2 O 3 nanocrystals. The PVDF membrane with inclusion of α-Fe 2 O 3 nanorods showed high degradation efficiency (90%) because of the higher surface Fe 3+ density. The water flux and degradation kinetics of the composite membrane were also studied. [ABSTRACT FROM AUTHOR]

We studied structure and oxygen-sensitive photoluminescence (PL) of ZrO 2 :Eu,Nb nanocrystalline powders synthesized via a sol-gel route and heat-treated up to 1200 °C. The material containing only 2 at% Eu 3+ was predominantly monoclinic, whereas 8 at% of Eu 3+ stabilized tetragonal phase. Comparable amount of niobium co-doping effectively suppressed the formation of tetragonal phase. PL of Eu 3+ ions was observed under direct excitation at 395 nm. PL decay kinetics showed that the luminescence was partially quenched, depending on doping concentrations and ambient atmosphere. At 300 °C, the PL intensity of all samples systematically responded (with up to 70% change) to changing oxygen content in the O 2 /N 2 mixture at atmospheric pressure. At low doping levels, the dominant factor controlling the PL intensity was an energy transfer from excited PL centers to randomly distributed defects in the ZrO 2 lattice. We argue that the charge transfer between the defects and adsorbed oxygen molecules alters the ability of the defects to quench Eu 3+ luminescence. At high doping levels, another type of sensor response was observed, where some Eu 3+ emitters are effectively switched on or off by the change of ambient gas. A remarkable feature of the studied material is a reversing of the sensor response with the variation of the Nb concentration. [ABSTRACT FROM AUTHOR]

An improved derivative spectroscopy method is proposed to resolve elementary bands in experimental photoluminescence spectra with high accuracy. The main procedures of analysis and calculations in the frame of this method are described. The method is tested on a synthetic photoluminescence spectrum consisting of five elementary Gaussian bands. The resolution of our method applied to overlapped Gaussian bands is estimated depending on their bandwidths. The photoluminescence spectrum of ZnS:Mn nanocrystals obtained with a selfpropagating high-temperature synthesis is analyzed, using our derivative spectroscopy method. Six photoluminescence bands are found, with their peaks located at the wavelengths equal to 540, 559, 579, 600, 620 and 643 nm. [ABSTRACT FROM AUTHOR]

Abstract: Most attempts to emulate the mechanical properties of strong and tough natural composites using helicoidal films of wood‐derived cellulose nanocrystals (w‐CNCs) fall short in mechanical performance due to the limited shear transfer ability between the w‐CNCs. This shortcoming is ascribed to the small w‐CNC‐w‐CNC overlap lengths that lower the shear transfer efficiency. Herein, we present a simple strategy to fabricate superior helicoidal CNC films with mechanical properties that rival those of the best natural materials and are some of the best reported for photonic CNC materials thus far. Assembling the short w‐CNCs with a minority fraction of high aspect ratio CNCs derived from tunicates (t‐CNCs), we report remarkable simultaneous enhancement of all in‐plane mechanical properties and out‐of‐plane flexibility. The important role of t‐CNCs is revealed by coarse grained molecular dynamics simulations where the property enhancement are due to increased interaction lengths and the activation of additional toughening mechanisms. At t‐CNC contents greater than 5% by mass the mixed films also display UV reflecting behaviour. These damage tolerant optically active materials hold great promise for application as protective coatings. More broadly, we expect the strategy of using length‐bidispersity to be adaptable to mechanically enhancing other matrix‐free nanoparticle ensembles. [ABSTRACT FROM AUTHOR]

The thermal evolution of the conductivity of a VO2 film and database-obtained band gap Eg of film nanocrystallites is traced in the temperature range of -196°C < T < 100°C (77 K < T < 273 K); the level position of donor impurity centers is determined to be Ed = 0.04 eV. It is shown that energy Eg decreases from 0.8 to ∼0 eV with an increase in temperature in the range of 273 K < T < 300 K, which is caused by the narrowing of the energy gap due to correlation effects and considered as the temperature-extended Mott “insulator-metal” electron phase transition with the monoclinic lattice symmetry retained. The subsequent jump in the symmetry from monoclinic to tetragonal with a further increase in temperature is considered as the Peierls structural phase transition, the temperature of which is in the vicinity of 340 K and determined by the size effects, nonstoichiometry of VO2 film nanocrystallites, and degree of their adhesion to the substrate. [ABSTRACT FROM AUTHOR]

It is essential to determine the elemental composition of doped functional materials, particularly for nanometer scale semiconductors, to guide synthesis and interpret physical phenomena. This study applied laser induced breakdown spectroscopy (LIBS) for elemental analysis of halides in perovskite type quantum dots, i.e., CsPbX3 nanocrystals (NCs). The optimum LIBS delay time and laser energy were experimentally determined, and small quantities of CsPbX3 NCs (μg) with different Cl/Br ratios and different photoluminescence (PL) properties were measured. Coefficients to correlate weight and LIBS emission intensity ratios for Cl and Br were experimentally determined from CuBr2/CaCl2 mixtures. The measured Cl/Br weight ratios correspond to NC PL emission wavelengths and the supplied amount of PbCl2 precursor. The proposed LIBS approach showed better sensitivity and stability than electron dispersive spectroscopy. Ideal detection accuracy and precision could be realized using LIBS, requiring only trace amounts of NC samples and simple pretreatment processes, with NC integrity retained until the test. [ABSTRACT FROM AUTHOR]

In this study, the high quality CdSe nanocrystals (NCs) capped with stearic acid were synthesized in a solvent and then purified four times by using the precipitation and redissolution process. The average size of the synthesized CdSe NCs was determined ~ 3.0 nm via transmission electron microscopy (TEM) measurement and their corresponding optical band edge energy was also calculated as ~ 2.1 eV using ultraviolet-visible (UV–Vis) absorption spectroscopy. The bulk heterojunction (BHJ) hybrid solar cells based on a ternary system including P3HT, PCBM and CdSe NCs at different weight concentrations (0 wt%, 0.1 wt%, 0.5 wt%, 1 wt% and 2 wt%) were fabricated by spin-casting process. The effect of the concentration of CdSe NCs on the photovoltaic parameters of these BHJ organic solar cells was investigated. The surface morphology of the photoactive layer modified by the incorporation of CdSe NCs into P3HT:PCBM matrix was observed with scanning electron microscopy (SEM). It was shown that when the concentration of CdSe NCs increases above 0.1 wt% in this ternary system, the photovoltaic performance of the devices significantly decreases. The power conversion efficiency of the organic photovoltaic (OPV) device was enhanced ~ 20% by incorporating CdSe NCs with 0.1 wt% with respect to those without CdSe NCs. [ABSTRACT FROM AUTHOR]

Self-healing can protect materials from diverse damages, but is intrinsically difficult in metals. This paper demonstrates a potential method through a simultaneous decomposition and oxidation of Ti 3 SiC 2 to achieve healing of stress cracking on the surface of nickel aluminum bronze (NAB)/Ti 3 SiC 2 nanocrystalline composites during fretting wear. At the finest nanocrystalline materials, a crack recovery would be attained at 76.5%. The repetitive fretting wear leads to a modest amount of ‘flowability’ of Ti 3 SiC 2 toward the crack, facilitating crack recovery. Along with the wear-triggered self-healing, the NAB/Ti 3 SiC 2 shows an improved tribological performance with the stable decreased friction torque due to the formation of lubrication TiO 2 oxide. [ABSTRACT FROM AUTHOR]

In this study Ag 2 S@SnS 2 core-shells were synthesized successfully for the first time. Pulsing microwave irradiation was quite an effective technique for the controlled growth of core-shells using a one pot technique. Different parameters were optimized in the synthesis of core-shells and they were verified structurally using X-ray diffraction (XRD), Energy dispersive x-ray spectroscopy (EDX), Transmission electron microscopy (TEM) and Fourier Transform Infrared Spectroscopy (FTIR). Ultraviolet-Visible spectroscopy (UV–Vis) revealed a strong absorption at 805 nm. Photoluminescence spectroscopy (PL) showed that the samples had a considerable emission around 870 nm and it was stable for at least 30 days in water. EDX analysis confirmed the presence of Sn, Ag and S atoms in the samples and their atomic ratio was quite close to their nominal chemical values. XRD analysis showed the formation of Ag 2 S monoclinic and SnS 2 hexagonal phases. TEM images showed clearly formation of core-shells with sizes below 10 nm. FTIR spectroscopy revealed that thioglycolic acid (TGA) is an effective and stable capping agent for the synthesis of Ag 2 S@SnS 2 core-shells using this pulsing technique. [ABSTRACT FROM AUTHOR]

YVO 4 : Yb 3+ ,Er 3+ upconverting nanocrystals were synthesized via a hydrothermal method using different compounds as surfactants. Structure and morphology of the nanocrystals were investigated by X-ray diffraction and transmission electron microscopy. Tetragonal crystal structure of the nanocrystals appeared irrespective of the type of surfactant used. The average crystallite size was estimated by TEM images. The obtained products were composed of small nanoparticles, in the size range of 10–60 nm, depending on the surfactant used. The morphology of the nanoparticles was also regulated by the type of surfactant. Spectroscopic analysis of the materials obtained was carried out by measuring the emission and excitation spectra and the intensity of luminescence as a function of laser energy and luminescence decays. The nanocrystals prepared exhibited a green upconversion emission attributed to the 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions of Er 3+ , under NIR (985 nm) pulse laser irradiation, and their emission lifetimes were in the range 3.84–4.90 μs. On the basis of the spectroscopic investigation, the upconversion mechanism was proposed and chromaticity coordinates were calculated. Surfactants were found to influence on chromaticity of luminescence. [ABSTRACT FROM AUTHOR]

This paper studies a new CsI: Eu 2+ nanocrystal was synthesized via the sol-gel method. The structural properties of CsI: Eu 2+ nanocrystal were characterized by Scanning Electron Microscope (SEM). Optical properties were followed by absorption and emission spectroscopy. Two absorption band peaking at 300 and 370 nm and two emission band with a maximum of 420 and 500 nm were observed. The dominance of 4f 6 5d → 4f 7 radiative transitions which were observed for the Eu bands in CsI nanocrystal caused these luminescence bands. Scintillation spectra and decay curve to alpha particles of the sample were monitored and they compared with the results obtained in pure CsI nanocrystal. [ABSTRACT FROM AUTHOR]

Pulsed cathodoluminescence spectra and luminescence decay kinetics of WS 2 nanocrystals were studied under a high energy electron pulse excitation. Increasing electron energy density inputs to the WS 2 nanocrystals lead to enhancement of the electron-hole number and their lifetimes. The maximum luminescence intensity is reached for the highest electron energy dose. The electrons, interacting with WS 2 nanocrystals, form defect vacancies, wherein excited electron-holes create bound excitons which further recombine as a distinct sub-band gap emission. The lifetime of bound excitons does not depend on increasing electron doses due to the limitation of the enhancing number of bound excitons by increasing density of defects, which are radiative recombination active centers. The number of bound excitons, i.e. luminescence intensity, is proportional to the density of defects, which can be tuned by electron doses. Micro-photoluminescence measurements of the WS 2 monolayer showed formation of excitons and trions. [ABSTRACT FROM AUTHOR]

Crystalline phase evolution through merely adjusting composition was achieved in silicate glass ceramics containing Lu n O n-1 F n+2 (n = 5–10) nanocrystals. Orthorhombic or cubic phase nanocrystals were precipitated in the aluminosilicate glass matrix after thermal treatment together with varying the Na 2 O/NaF ratio. Oxyfluoride nanocrystals with quasi-spherical shape show homogenous and dense distribution in glass matrix by transmission electron microscopy measurement. Intense upconversion and mid-infrared emissions were realized in these glass ceramics compared to the precursor glass, and the emission spectral shapes, relative emission intensity and fluorescence decay curves of Er 3+ in cubic LuOF embedded samples exhibit remarkable differences due to the crystal phase dependent effect in glass ceramics. These results indicate that the crystallization and luminescence properties of oxyfluoride glass ceramics could be modified through the alteration of glass composition, which could be used for the development of novel glass ceramics and design of luminescent properties. [ABSTRACT FROM AUTHOR]

Different compositions of europium doped aluminosilicate oxyfluoride glass ceramics prepared in air atmosphere have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy methods. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show presence of homogenously distributed SrF 2 nanocrystals after the heat treatment of the precursor glass. Efficient Eu 3+ incorporation in the high symmetry environment of glass ceramics is observed from the photoluminescence spectra. EPR spectra indicate Eu 3+ → Eu 2+ reduction upon precipitation of crystalline phases in the glass matrix. For composition abundant with Eu 2+ in the glassy state such behaviour is not detected. Local structure around europium ions is discussed based on differences in chemical compositions. [ABSTRACT FROM AUTHOR]

The ultrasmall Yb/Er: CaF 2 NCs are chosen as an example to certify the upconversion emission intensity can be greatly enhanced through combining various approaches together, including doping Na + ions to promote the growth the particle size and tailor the crystal-field environment of the emitters, control shell thickness to lower the non-radiative decay and tune Yb 3+ concentration in the shell to enhance the absorption of the excitation energy. In comparison with Na + -free 20Yb/2Er: CaF 2 NCs (~ 2 nm), the upconversion luminescence of 20Yb/2Er: CaF 2 @10Yb: CaF 2 NCs (~ 9 nm) containing ~ 0.5 mmol Na + ions in the core and 10% Yb 3+ in the shell with 5 nm thickness intensifies for about 95 times. [ABSTRACT FROM AUTHOR]

According to the principle of detailed balance, the luminescence intensity at a wavelength λ 1 as a result of excitation at a wavelength λ 2 must be related in some way to the luminescence intensity at λ 2 as a result of excitation at λ 1 . In 1926, E. H. Kennard derived such a relation by applying the concept of the Einstein coefficients to some model system. Our study provides a general thermodynamic proof that Kennard's relation is valid for arbitrary macroscopic photoluminescent bodies. An experimental test of this relation is also given for InP/ZnS core-shell colloidal quantum dots synthesized by the conventional high-temperature organometallic procedure. For these particles, the emission spectra at various excitation wavelengths and the photoluminescence excitation spectra at various emission wavelengths have been obtained. It was found that Kennard's relation does hold for the obtained spectra. [ABSTRACT FROM AUTHOR]

Halide perovskites have attracted enormous attention as a novel optoelectronic material showing bright emission recently. In this paper, we chose CsPbX 3 nanocrystals (NCs) as an example to study the structural, morphological and optical properties. We have synthesized monodispersed colloidal inorganic cesium lead halide perovskites (CsPbX 3 , X = Cl, Br and I, or mixed lead halide CsPb(Cl/Br) 3 and CsPb(Br/I) 3 ) NCs with various morphologies and brightly luminescent properties. The emission wavelength of resulting CsPbX 3 NCs can be tuned from 440 nm to 696 nm by varying the amount of different PbX 2 (X = Cl, Br and I), while maintaining high quantum yields up to 95% and narrow emission spectra. The average lifetime of the NCs is several ns to hundred with changing the composition. The blinking of the NCs in terms of a binary (on/off) process is different from II-VI quantum dots. Interestingly, we find that CsPbBr 3 NCs to Cs 4 PbBr 6 NCs or a mixture of CsPbBr 3 NCs and Cs 4 PbBr 6 NCs were obtained by adjusting the amount of oleic acid (OA)-Cs precursor. The optical properties of these NCs have been controlled by varying their composition. Moreover, the injection speed of Cs-OA precursor enables the control of CsPbI 3 NCs with different morphology, which can be tuned from litter nanoparticles to uniform nanorods. This finding can serve as an ideal platform for the investigation of fundamental properties. [ABSTRACT FROM AUTHOR]

In this paper, We investigate the morphology effect of Aluminum-doped zinc oxide (AZO) thin films on the physical properties such as conductivity and grain size. The AZO thin films are prepared by spray pyrolysis at different thicknesses in the range 100–400 nm. Height fluctuations obtained from atomic force microscopy (AFM) analysis are applied to the statistical and fractal analysis of thin films. We show that the conductivity of thin films is proportional to the roughness parameter as σ ∼ W m which m = 6 . 42 ± 0 . 50 . Calculating the nonlinear measures (skewness and kurtosis) of height fluctuations demonstrates the isotropic nature of AZO rough surfaces. Fractal analysis of the mentioned thin films using two dimensional multifractal detrended fluctuation analysis illustrates the multifractality scaling and the strength of multifractality increases with thickness. Our results show that the reason for the multi-affinity is the existence of different correlations in the height fluctuations of the thin films. Calculating the contour loops features of the height fluctuations reveals that the radius, length, and area of loops increase with thickness enhancement and the radius of contour loops is introduced as a new statistical parameter which is linearly related to the grain size and could be useful to calculate it. [ABSTRACT FROM AUTHOR]

The absorption, photoluminescence, and photoluminescence excitation spectra of CdS nanocrystals formed by the Langmuir-Blodgett method are explored. Features of the absorption and photoluminescence excitation spectra defined by optical transitions in the matrix and nanocrystals are identified. The efficiency of electronic excitation transfer from an organic matrix to nanocrystals is studied. It is shown that charge carriers efficiently transfer from the matrix to electron and hole size-quantization levels in nanocrystals and to acceptor defect levels in the band gap of nanocrystals. A large Stokes shift defined by fine exciton structure (bright and dark excitons) is observed. The shift is in the range 140-220 meV for nanocrystals 2.4 and 2.0 nm in radius. [ABSTRACT FROM AUTHOR]

Cesium-based perovskite nanocrystals (NCs) have outstanding photophysical properties improving the performances of lighting devices. Fundamental studies on excitonic properties and hot-carrier dynamics in perovskite NCs further suggest that these materials show higher efficiencies compared to the bulk form of perovskites. However, the relaxation rates and pathways of hot-carriers are still being elucidated. By using ultrafast transient spectroscopy and calculating electronic band structures, we investigated the dependence of halide in Cs-based perovskite (CsPbX3 with X=Br, I, or their mixtures) NCs on the hot-carrier relaxation processes. All samples exhibit ultrafast (<0.6 ps) hot-carrier relaxation dynamics with following order: CsPbBr3 (310 fs)>CsPbBr1.5I1.5 (380 fs)>CsPbI3 NC (580 fs). These result accounts for a reduced light emission efficiency of CsPbI3 NC compared to CsPbBr3 NC. [ABSTRACT FROM AUTHOR]

Fluorophosphate glasses doped with ZnS are studied. The properties of ZnS nanocrystals formed are determined using X-ray-diffraction analysis and optical spectroscopy. The size and the band-gap width of these crystals are determined by the Tauc method. It is shown that ZnS nanocrystals luminesce in the visible spectral region with a low (2-3%) absolute quantum yield. [ABSTRACT FROM AUTHOR]

The spatiotemporal regulation of light-gated ion channels is a powerful tool to study physiological pathways and develop personalized theranostic modalities. So far, most existing light-gated channels are limited by their action spectra in the ultraviolet (UV) or visible region. Simple and innovative strategies for the specific attachment of photoswitches on the cell surface without modifying or genetically encoding channel structures, and more importantly, that enable the remote activation of ion-channel functions within near-infrared (NIR) spectral window in living systems, remain a challenging concern. Herein, metabolic glycan biosynthesis is used to achieve site-specific covalent attachment of near-infrared-light-mediated lanthanide-doped upconversion nanocrystals (UCNs) to the cell surface through copper-free click cyclization. Upon irradiation with 808 nm light, the converted emission at 480 nm could activate a light-gated ion channel, channelrhodopsins-2 (ChR2), and thus remotely control the cation influx. This unique strategy provides valuable insights on the specific regulation membrane-associated activities in vivo. [ABSTRACT FROM AUTHOR]

Mesocrystalline particles have been recognized as a class of multifunctional materials with potential applications in different fields. However, the internal organization of nanocomposite mesocrystals and its influence on the final properties have not yet been investigated. In this paper, a novel strategy based on electrodynamic simulations is developed to shed light on how the internal structure of mesocrystals influences their optical properties. In a first instance, a unified design protocol is reported for the fabrication of hematite/PVP particles with different morphologies such as pseudo-cubes, rods-like and apple-like structures and controlled particle size distributions. The optical properties of hematite/PVP mesocrystals are effectively simulated by taking their aggregate and nanocomposite structure into consideration. The superposition T-Matrix approach accounts for the aggregate nature of mesocrystalline particles and validate the effective medium approximation used in the framework of the Mie theory and electromagnetic simulation such as Finite Element Method. The approach described in our paper provides the framework to understand and predict the optical properties of mesocrystals and more general, of hierarchical nanostructured particles. [ABSTRACT FROM AUTHOR]

In this paper e-beam evaporation technique is used for nc-Si film deposition rather than conventional plasma enhanced chemical vapor deposition (PECVD). In present work, the nc-Si films of different thicknesses (100, 150 and 200 nm) was deposited on Corning glass 1737 substrate using e-beam evaporation method with controlled beam current and deposition rate at moderately low temperature. The deposited nc-Si films were further characterized using FESEM, EDS, XRD, Raman Spectroscopy and AFM. The results of XRD and RAMAN confirm the nanocrystalline nature of the deposited film and the FESEM and AFM results demonstrate that the grain size increases with the increase in film thickness. To validate the feasibility of deposited film for TFT application, conductivity measurement is carried using 4-probe technique. The results indicate that e-beam evaporation is the cost effective alternative of PECVD and controlled grain size and density of nc-Si film can be easily achieved. [ABSTRACT FROM AUTHOR]

0D transition metal phosphides (TMPs) nanocrystals (NCs)-2D ultrathin black phosphorus (BP) heterostructure (Ni2P@BP) have been synthesized via a facile sonication-assisted exfoliation followed by a solvothermal process. Compared with the bare BP, the specially designed Ni2P@BP architecture can enhance the electrical conductivity (from 2.12 × 102 to 6.25 × 104 S m-1), tune the charge carrier concentration (from 1.25 × 1017 to 1.37 × 1020 cm-3), and reduce the thermal conductivity (from 44.5 to 7.69 W m-1 K-1) at 300 K, which can be considered for multiple applications. As a result, the Ni2P@BP exhibits excellent Li storage properties and high hydrogen evolution reaction electrocatalytic activities. The Ni2P@BP shows improved Li diffusion kinetics (e.g., the Li ions diffusion coefficient increases from 1.14 × 10-14 cm2 s-1 for pure BP nanosheets to 8.02 × 10-13 cm2 s-1 for Ni2P@BP). In addition, the Ni2P@BP electrode sustains hydrogen production with almost unchanged activity over 3000 cycles, which indicates its good chemical stability when operating under strong reducing environment. [ABSTRACT FROM AUTHOR]

Effect of cerium substitution in Nanocrystalline magnesium ferrite, $$\hbox {MgCe}_x\hbox {Fe}_{2-x}\hbox {O}_{4}$$ ( $$x = 0.00, 0.02, 0.04$$ and 0.06) synthesized by sol-gel auto-combustion process has been studied. X-ray diffraction reveals the single-phase cubic spinel structure, X-ray density and porosity increase with concentration of ceria. Scanning electron microscopy micrograph shows agglomeration of ceria. Fourier transform infrared spectroscopy confirms the formation of spinel phase with two frequency bands, $${\nu }_{1}$$ at around $$590\,\hbox {cm}^{-1}$$ and a lower frequency band $${\upnu }_{2}$$ at $$430\,\hbox {cm}^{-1}$$ , which were attributed to intrinsic vibrations of tetrahedral group (A-site) and octahedral groups (B-sites), respectively, based on this the cation distribution is proposed as $$(\hbox {Mg}_{y-x}^{2+}\,\hbox {Fe}_{ 1-y+x}^{3+})_{\mathrm{A}}[\hbox {Mg}_{1-y}^{2+}\,\hbox {Fe}_{ 1+y-x}^{3+} \hbox {Ce}_{x}^{3+}]_\mathrm{B}\,\hbox {O}_{4}^{2-}$$ . The force constant for tetrahedral sites was less than that of octahedral sites. X-ray photoelectron spectroscopy spectra reveals the oxidation state of Fe by two peaks in the region of 712 and 724 eV corresponding to $$2p_{3/2}$$ and $$2p_{1/2}$$ , respectively, with $$\Delta E = 12$$ eV. The chemical state of Ce was confirmed by peaks at BE 884 and 902 eV corresponding to $$3d_{5/2}$$ and $$3d_{3/2}$$ , respectively. vibrating sample magnetometer studies show that the magnetization strongly depends on $$\hbox {Ce}^{3+}$$ substitutions. Saturation magnetization has decreased up to $$x=0.04$$ and then increased which can ascribed to decrease in canting angle. All the samples were in superparamagnetic state. [ABSTRACT FROM AUTHOR]

Nonlinear optical trans-4'-(dimethylamino)-N-methyl-4-stilbazolium tosylate (DATS) nanocrystals are synthesized in polymethylmethacrylate by nucleation in a drying polymer film at different solvent concentrations. Nanocrystals with sizes progressively increasing from 70 to 2500 nm are obtained. The effect of size on the nonlinear optical coefficient is studied by generation of the second harmonic of a 1064-nm Nd:YAG laser. It is shown that the nonlinear optical coefficient decreases with decreasing crystal size by no more than a factor of 1.5. The optical absorption spectra and the shape of nanocrystals are studied as functions of their size. [ABSTRACT FROM AUTHOR]

In this work, self-assembled Ge quantum dot (QD) formation in a dielectric matrix is explored. Of particular interest were their structural and optical properties, in order to understand the stress build-up in such a process and its impact on the material properties during processing. To this end, thin films consisting of (Ge + SiO2)/SiO2 multilayers grown by RF magnetron sputtering were deposited at room temperature. Annealing of such films at 873 K in inert N2 atmosphere produced, at the position of the Ge-rich SiO2 layers, a high lateral density (about 1012 cm−2) of Ge QDs with a good crystallinity. SiO2 spacer layers separated the adjacent Ge-rich layers, where the Ge QDs were formed with a diameter of about the size of the (Ge + SiO2) as-deposited layer thickness, and created a good vertical repeatability, confirmed by the appearance of a Bragg sheet in two-dimensional small-angle X-ray scattering patterns. The structural analysis, by wide-angle X-ray diffraction, grazing-incidence small-angle X-ray scattering and transmission electron microscopy, has shown that the described processing of the films induced large compressive stress on the formed QDs. Optical analysis by time-resolved photoluminescence (PL) revealed that the high density of crystalline Ge QDs embedded in the amorphous SiO2 matrix produced a strong luminescence in the visible part of the spectrum at 2-2.5 eV photon energy. It is shown that the decay dynamics in this energy range are very fast, and therefore the transitions that create such PL are attributed to matrix defects present in the shell surrounding the Ge QD surface (interface region with the matrix). The measured PL peak, though wide at its half-width, when analysed in consecutive short spectral segments showed the same decay dynamics, suggesting the same mechanism of relaxation. [ABSTRACT FROM AUTHOR]

A Pd nano-polycrystalline microstructure was simulated by molecular dynamics, including edge or screw dislocations in one of the 50 grains, so as to produce a realistic model of nanocrystalline domain with line defect. The same crystalline domain was also studied, with or without line defects, as a free-standing, isolated nanocrystal. Atomic coordinates of the selected domain were used to generate powder patterns by means of the Debye scattering equation, and these patterns were used as 'experimental' data to test existing methods of line profile analysis in controlled condition, i.e., with known type and density of defects. Results show that the Krivolgaz-Wilkens theory of dislocation line broadening qualitatively agrees with the MD model, but errors can be larger than 50 pct. A critical issue arises from the instability of the Krivolgaz-Wilkens model when all line profile parameters are simultaneously refined: reasonable results can be obtained by fixing or restricting some parameters. [ABSTRACT FROM AUTHOR]

The effect of synthesis conditions for BEA zeolite nanocrystals (BEA-ZNC) on the combination of their morphological, textural, and acidic properties has been studied. BEA-ZNC have been synthesized by the hydrothermal or vapor-phase crystallization of reaction mixtures with a high template concentration using the following variable synthesis parameters: the SiO/AlO ratio the presence of mineralizing additives, the SiO source and template type, and the synthesis pH. It has been found that an increase in the aluminum content in BEA-ZNC from 2.7 to 7.8 Al atoms per unit cell is accompanied by a decrease in the size of the ZNC from 250-350 to 100 nm, an increase in the acid site concentration, and an increase in the fraction of weak acid sites in the acidity range of the samples. It has been shown that the specific feature of the synthesis of BEA-ZNC is a low degree of inclusion of silica and the template into the zeolite composition, which is 28-62 and 3.4-5.5%, respectively, of the amounts initially introduced into the reaction mixture. It has been proposed that silica gel should be used as the most promising SiO source for the preparation of BEA-ZNC; the use of silica gel provides formation of a material in the form of isolated nanocrystals with a size of 150-300 nm, a developed pore structure, and a high concentration of acid sites. It has been shown that the BEA-ZNC synthesized by vapor-phase crystallization are inferior to the samples prepared by conventional hydrothermal crystallization with respect to the pore structure characteristics and acidic properties. [ABSTRACT FROM AUTHOR]

A controllable approach to the formation of III- nitride nanocrystalline structures using hydrothermal assisted method is presented. The structural and morphological properties of the prepared nanostructures are analyzed using X-ray diffraction, Fast Fourier Transformation and transmission electron microscope techniques. The temperature dependent structural formation of nitride nanostructures have been systematically investigated using X-ray diffraction. Raman spectra of the samples grown at optimized condition exhibited different phonon modes of the respective nitrides (GaN, InN and In x Ga 1−x N). Nanoparticles and nanorods formation of the indium nitride and indium gallium nitride are observed in the TEM micrographs. FFT analysis revealed that the synthesized III-nitride nanostructures are of good crystalline quality. Nanorods of these nitrides showed better crystalline quality than the nanoparticles in the FFT reflections. [ABSTRACT FROM AUTHOR]

We report the total structure determination of a large bimetallic nanocluster with an overall composition of [Au80Ag30(C≡CPh)42Cl9]Cl. It is the largest structurally characterized bimetallic coinage nanocluster so far. The 110 metal atoms are distributed in a concentric four-shell Russian doll arrangement, Au6@Au35@Ag30Au18@Au21. There are 42 PhC≡C-- ligands and 9 μ2-chloride ligands clamping on the cluster surface. The chloride is proven to be critical for the formation of this giant cluster, as the control experiment in the absence of halide gives only smaller species. This work demonstrates that the halide can play a key role in the formation of a large metal nanocluster, and the halide effect should be considered in the design and synthesis of metal nanoclusters. [ABSTRACT FROM AUTHOR]

A dual-space approach, combining Rietveld and pair distribution function (PDF) analyses, has been applied to temperature-dependent synchrotron X-ray total scattering data collected on vapor diffusion sol–gel derived CaMoO4 nanocrystals. A sharp transition in Ca–O bond distances in the range of 151–163 K was identified by PDF analysis, which is attributed to the thermal activation of rotational disorder associated with the rigid MoO4 tetrahedra. [ABSTRACT FROM AUTHOR]

The interactions between methylene blue (MB) and zeolite nanocrystals in water suspensions are investigated. The zeolite nanocrystals (diameter of 40–70 nm) with BEA-, LTL- and LTA-type framework structures with pore size of 7.3, 7.1 and 4.1 Å, respectively, are chosen to evaluate their effect on the stabilization of the MB (7.0 × 16 Å) in their pores and on the crystals surface. It is found that the MB molecules enter the channels of the LTL-type zeolite nanocrystals, while the BEA-type zeolite is partially filled by the MB due to the presence of organic agent (tetraethylammonium cations) in the channels. The highly hydrophilic surface of the LTA-type nanocrystals with pore size smaller than the size of MB is strongly modified, but no MB molecules in the LTA-zeolite channels are present due to pore size restriction. The UV-vis characterization of the suspensions containing zeolite nanocrystals and MB (samples LTL-MB, BEA-MB and LTA-MB) reveal a shift in the absorption maximum (581 nm) with 16.5 nm for BEA, 15.5 nm for LTL, and 13.5 nm for LTA zeolite crystals. The absorption maximum in the three suspensions shifts to shorter wavelengths (blue shift) with time, and only the LTA-MB sample returns to 581 nm after 8 minutes that corresponds to the original wavelength of the free MB molecule in water. The observed blue shift for samples BEA-MB and LTL-MB is explained with the penetration and stabilization of MB molecules in the zeolite pores. The zeolite nanocrystals in the presence of MB show high stability in water suspensions, which make them a promising matrix for preparation of water-soluble photopolymers. Photopolymers for full colors holography with expanded wavelength sensitivity range based on addition of more than one sensitizer (MB, erythrosine B and acriflavine stabilized in zeolite nanocrystals) are under development. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) spectroscopy complemented with X-ray diffraction, X-ray fluorescence, and optical spectroscopy was used to study nanocrystalline CeO2 powder samples that exhibit weak room-temperature ferromagnetism. EPR lines assigned to the Ce3+ trigonal sites were found for the first time in cerium dioxide that contains a trace impurity of Mn2+. This finding indicates that manganese dopant facilitates the conversion of the oxidation state of Ce4+ to Ce3+ in nanocrystalline CeO2. Our results support the view that Ce3+/Ce4+ pairs along with defects on the surface of nanoparticles are responsible for the ferromagnetism in CeO2. The EPR study reveals that the charge-transfer mechanism proposed recently is more suitable to explain the origin of room-temperature ferromagnetism in CeO2 than the F+-centers exchange interactions. [ABSTRACT FROM AUTHOR]