Pulsed laser induced synthesis of scheelite-type colloidal nanoparticles in liquid and the size distribution by nanoparticle tracking analysis

Pulsed laser ablation (PLA) of ceramic target in liquid phase was successfully employed to prepare calcium tungstate (CaWO₄) and calcium molybdate (CaMoO₄) colloidal nanoparticles. The crystalline phase, particle morphology and optical property of the colloidal nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The produced stable colloidal suspensions consisted of the well-dispersed nanoparticles showing a spherical shape. The mechanism for the laser ablation and nanoparticle forming was discussed under consideration of photo-ablation process. Nanoparticle tracking analysis using optical microscope combined with image analysis was proposed to determine the size distribution function of the prepared colloidal nanoparticles. The mean size of the CaWO₄ and CaMoO₄ colloidal nanoparticles were 16 and 29 nm, with a standard deviations of 2.1 and 5.2 nm, respectively.     

Laser-induced synthesis of BaMoO<Subscript>4</Subscript> nanocolloidal suspension and its optical properties

Pulsed laser ablation in a liquid phase was successfully employed to synthesize a barium molybdate (BaMoO₄) nanocolloidal suspension. The nanocolloidal suspension was composed of well-dispersed and horizontally assembled BaMoO₄ aggregates. The BaMoO₄ aggregates showed predominantly elliptically shaped nanorods with sizes between 100 and 200 nm. The preferential elliptical growth was rationalized from the viewpoint of the intrinsic structure of BaMoO₄. The optical properties of the prepared BaMoO₄ colloidal nanoparticles were investigated using Raman spectroscopy, UV–vis spectroscopy and photoluminescence (PL) spectrophotometry. The optical band gap was estimated by Tauc and Menth’s law. The PL emission feature was decomposed into several individual Gaussian components, which could be interpreted by a Jahn–Teller splitting effect on the [MoO₄]^2- tetrahedron of the BaMoO₄ colloidal nanoparticles. PACS  42.62.-b; 82.70.Dd; 78.55.Hx; 81.07.Wx     

Tunable emission and efficient energy-transfer properties of Ce<Superscript>3+</Superscript> and Mn<Superscript>2+</Superscript> co-doped Ba<Subscript>3</Subscript>Gd(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphors

MgO powders subjected to Q-switched laser pulses in water were characterized by X-ray/electron diffraction and optical spectroscopy to have a significant optical property change with accompanied transformation into the phase assemblages of periclase, brucite and liquid-crystalline lamella. The periclase nanoparticles tended to have {111} habit planes parallel to the basal layers of lamella and brucite flakes more or less rolled as fibers, ribbons or tubes. A significant internal compressive stress was built up for periclase and brucite but not the more flexible lamellar phase. The colloidal suspension containing the densified periclase nanoparticles within the rolled brucite/lamellae flakes showed UV–visible absorption corresponding to a minimum band gap of ca. 5 eV.     

Bandgap-width correction for luminophores CaMoO<Subscript>4</Subscript> and CaWO<Subscript>4</Subscript>

Submicron-powder luminophores CaMoO₄ and CaWO₄ obtained via solid-phase reactions have been studied using diffuse-reflection (DR) spectroscopy and photoluminescence (PL) spectroscopy. It is found that the diffuse-reflection spectrum in the range of a fundamental absorption edge of <300 nm is distorted by PL overlapping, so that subsequent calculations of optical band gap E _g of luminophores CaMoO₄ and CaWO₄ result in an overestimation of this value. An algorithm for the correct processing of diffuse-reflection spectra is described. It is based on a subtraction of the photoluminescence spectrum in the range of fundamental absorption. The correct E _g values and energy values for the defect levels in the bandgap of CaWO₄ and CaMoO₄ are determined to amount to 4.78, 4.83, and 4.86 ± 0.01 eV and 3.97, 4.07, 4.16 ± 0.01 eV, respectively.     

Photoinduced toxicity of PrF<Subscript>3</Subscript> and LaF<Subscript>3</Subscript> nanoparticles

PrF₃ and LaF₃ nanoparticles were synthesized by the hydrothermal method. The size distribution of these nanoparticles in the colloidal solution produced was studied by photon correlation spectroscopy. The mean diameter of the nanoparticles was 42 ± 1 nm. During the study of the toxicity of the nanoparticles, the mixture of a colloidal solution of the nanoparticles with cells to be studied was irradiated by 30-mW continuous lasers at wavelengths of 532 and 473 nm. The concentration of salmonella cells in normal saline was 10⁶ cell/mL, while that of nanoparticles was 0.1 g/L. The cell survival percentage was 39, 34, and 20% for the irradiation times of 5, 10, and 15 min, respectively, at an optimal laser radiation power density of 0.4 W/cm at a wavelength of 532 nm. It was ascertained that LaF₃ nanoparticles do not possess the property of photoinduced toxicity and the apoptosing effect. Moreover, the property of photoinduced toxicity is not shared by microparticles, in contrast to nanoparticles.     

Structural and optical properties of novel surfactant-coated Yb@TiO<Subscript>2</Subscript> nanoparticles

In this paper a novel hybrid approach to synthesise composite nanoparticles is presented. It is based on the laser ablation of a bulk target (Yb) immersed in a reversed micellar solution which contains nanoparticles of a different host material (TiO₂ nanoparticles) previously synthesised by chemical method. This approach thus exploits the advantages of the chemical synthesis through reversed micellar solution (size control, nanoparticle stabilisation), and of the laser ablation (“clean” synthesis, no side reactions). Central role is played by the microscopic processes controlling the deposition of the ablated Yb atoms onto the surface of TiO₂ nanoparticles which actually behave as nucleation seeds. The structural features of the resulting Yb@TiO₂ composite nanoparticles have been studied by Transmission Electron Microscopy, whereas their peculiar optical properties have been explored by UV–Vis spectroscopy and steady-state fluorescence. Results consistently show the formation of Yb and TiO₂ glued nanodomains to form nearly spherical and non-interacting nanoparticles with enhanced photophysical properties.     

Pd2+ reduction and gasochromic properties of colloidal tungsten oxide nanoparticles synthesized by pulsed laser ablation

Tungsten oxide nanoparticles were fabricated by a pulsed laser ablation method in deionized water using the first harmonic of a Nd:YAG laser (λ=1064 nm) at three different laser pulse energies (E1 =160, E2 =370 and E3 =500 mJ/pulse), respectively. The aim is to investigate the effect of laser pulse energy on the size distribution and gasochromic property of colloidal nanoparticles. The products were characterized by dynamic light scattering (DLS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. The results indicated that WO₃ nanoparticles were formed. After ablation, a 0.2 g/l PdCl₂ solution was added to activate the solution against hydrogen gas. In this process Pd²⁺ ions were reduced to deposit fine metallic Pd particles on the surface of tungsten oxide nanoparticles. The gasochromic response was measured by H₂ and O₂ gases bubbling into the produced colloidal Pd–WO₃. The results indicate that the number of unreduced ions (Pd²⁺) decreases with increasing laser pulse energy; therefore, for colloidal nanoparticles synthesized at the highest laser pulse energy approximately all Pd²⁺ ions have been reduced. Hence, the gasochromic response for this sample is nearly reversible in all cycles, whereas those due to other samples are not reversible in the first cycle.     

Synthesis and characterization of platinum nano sized particles by laser ablation in C<Subscript>2</Subscript>H<Subscript>6</Subscript>O<Subscript>2</Subscript> solution

Platinum nano sized particles (Pt NPs) are superior catalysts for many intentions, such as glucose sensors, cancer therapy, gas sensors, etc. Here, Pt NPs were produced by pulsed laser ablation in C₂H₆O₂ solution using Q-switched Nd:YAG laser, for the first time. Then, the influence of the laser fluence during synthesis of them was investigated; and they were characterized by UV–vis spectroscopy, TEM, FE-SEM, XRD, FT-IR, and Raman spectroscopy. The results showed that with increasing laser fluence, the mean particle size of the spherical NPs enhanced. Meanwhile, they had a polycrystalline cubic structure. Correspondingly, the plasmon peak position of generated NPs in the absorption spectra shifted from 257 to 266 nm, with a rise of laser fluence. The IR and Raman spectroscopy was used to achieve the information about the surface state of Pt NPs. We propose that the optimum adjusted laser fluence is an important factor to increase the ablation efficiency.     

Synthesis of Cu 2 O,CuCl, and Cu 2 OCl 2 nanoparticles by ultrafast laser ablation of copper in liquid media

Copper complex nanoparticles were fabricated from bulk copper using picosecond laser ablation in water and chloroform. We found that composition of the nanoparticles was CuCl and Cu₂OCl₂ in chloroform at three different input fluences; Cu₂O in water which was confirmed from the data of EDAX, UV-Visible absorption spectra, and selected area electron diffraction pattern. We have also performed nonlinear optical studies of colloidal nanoparticles using Z-scan technique at 800 nm and ～2 ps laser pulses. Cu₂O NPs exhibited two-photon absorption at lower peak intensities while three-photon absorption was observed at higher peak intensities. Other samples exhibited two-photon absorption at all peak intensities.     

Simple synthetic route for hydroxyapatite colloidal nanoparticles via a Nd:YAG laser ablation in liquid medium

Pulsed laser ablation (PLA) in liquid medium was successfully employed to synthesize hydroxyapatite (HAp) colloidal nanoparticles. The crystalline phase, particle morphology, size distribution and microstructure of the HAp nanoparticles were investigated in detail. The obtained HAp nanoparticles had spherical shape with sizes ranging from 5 to 20 nm. The laser ablation and the nanoparticle forming process were studied in terms of the explosive ejection mechanism by investigating the change of the surface morphology on target. The stoichiometry and bonding properties were studied by using XPS, FT-IR and Raman spectroscopy. A molar ratio of Ca/P of the prepared HAp nanoparticles was more stoichiometric than the value reported in the case of ablation in vacuum.     

Generation of MoS<Subscript>2</Subscript> quantum dots by laser ablation of MoS<Subscript>2</Subscript> particles in suspension and their photocatalytic activity for H<Subscript>2</Subscript> generation

MoS₂ quantum dots (QDs) have been obtained in colloidal suspensions by 532 nm laser ablation (7 ns fwhp/pulse, 50 mJ/pulse) of commercial MoS₂ particles in acetonitrile. High-resolution transmission electron microscopy images show a lateral size distribution from 5 to 20 nm, but a more homogeneous particle size of 20 nm can be obtained by silica gel chromatography purification in acetonitrile. MoS₂ QDs obtained by laser ablation are constituted by 3–6 MoS₂ layers (1.8–4 nm thickness) and exhibit photoluminescence whose λ_PL varies from 430 to 530 nm depending on the excitation wavelength. As predicted by theory, the confinement effect and the larger periphery in MoS₂ QDs increasing the bandgap and having catalytically active edges are reflected in an enhancement of the photocatalytic activity for H₂ generation upon UV–Vis irradiation using CH₃OH as sacrificial electron donor due to the increase in the reduction potential of conduction band electrons and the electron transfer kinetics.     

InTaO<Subscript>4</Subscript>-based nanostructures synthesized by reactive pulsed laser ablation

Nanostructured Ni-doped indium–tantalum–oxides (InTaO₄) were synthesized by a reactive pulsed laser ablation process, aiming at the final goal of direct splitting of water under visible sunbeam irradiation. The third harmonics beam of a Nd:YAG laser was focused onto a sintered In_0.9Ni_0.1TaO_4−δ target in pure oxygen background gases (0.05–1.00 Torr). Increasing the oxygen gas pressure, via thin films having nanometer-sized strong morphologies, single-crystalline nanoparticles were synthesized in the reactive vapor phases. The nanostructured deposited materials have the monoclinic layered wolframite-type structure of bulk InTaO₄, without oxygen deficiency.     

Pulsed laser deposition of TiO<Subscript>2</Subscript>: diagnostic of the plume and characterization of nanostructured deposits

Promising applications of TiO₂ nanostructures include the development of optical devices, sensors, photocatalysts and self-cleaning coatings. In view of their importance, research on the synthesis of nanosized TiO₂ is a particularly active field. In this work we report on the investigation of the effect of laser irradiation wavelength (Q-switched Nd:YAG laser at 532, 355 and 266 nm), the temperature of the substrate and the atmosphere of deposition (vacuum, Ar and O₂) that are suitable for obtaining nanostructured deposits from TiO₂ sintered targets. The ablation plume emission is characterized with spectral and temporal resolution by optical emission spectroscopy (OES), while the surface morphology and chemical states of the material deposited on a Si (100) substrate are examined by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM) and by X-ray photoelectron spectroscopy (XPS), respectively. Deposits with nanostructured morphology with grain size down to 40 nm and keeping the stoichiometry of the targets were obtained at high temperature, while the highest concentration of particulates was observed at the longest laser wavelength of 532 nm on a substrate heated up to 650°C. In situ characterization of the ablation plume, carried out by OES, indicated the presence of emissions assigned to Ti I, Ti II and O I.     

One-step synthesis of colloidal Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> and γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles at room temperature

A facile room-temperature synthesis has been developed to prepare colloidal Mn₃O₄ and γ-Fe₂O₃ nanoparticles (5 to 25 nm) by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant. The morphology of the as-prepared samples was observed by transmission electron microscopy. High-resolution transmission electron microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The magnetic properties of the samples were investigated with a superconducting quantum interference device magnetometer. The possible formation process has been proposed.     

Synthesis and characterization of a polyaniline-modified SnO<Subscript>2</Subscript> nanocomposite

Polyaniline-modified tin oxide and tin oxide nanoparticles were synthesized using a solution route technique. The obtained pristine products were characterized with X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and optical absorption spectroscopy. Thermogravimetric analysis results showed that the polyaniline-modified SnO₂ nanoparticles exhibit higher thermal stability than the SnO₂ nanoparticles. Scanning electron microscopy analysis on the as-synthesized powders showed spherical particle in the range of 50–100 nm.     

Nanostructured TiO<Subscript>2</Subscript> Films with a Mixed Phase for Perovskite Solar Cells

A series of thin films made with TiO₂ nanoparticles with a varied anatase/rutile phase ratio is prepared on conducting glass substrates using a spin-coating method. The structure, morphology, and optical properties of TiO₂ nanopowders and thin films fabricated are studied using powder X-ray diffraction, scanning electron microscopy, and optical spectroscopy. The TiO₂ nanostructured films created are used as photoelectrodes for the fabrication of perovskite solar cells (PSCs). The photovoltaic characteristics of PSCs under AM1.5 light illumination (1000 W/m²) under ambient conditions are studied. It is shown that the best efficiency of solar-to-electrical energy conversion, namely, 9.3%, is obtained for the PSC with a photoelectrode based on a TiO₂ film with an anatase/rutile mixed phase ratio of 86/14%.     

Induction of superconductivity of a La<Subscript>2</Subscript>CuO<Subscript>4</Subscript> thin film chemically oxidized by NaClO

High-quality, c-axis-oriented La₂CuO₄ thin films have been fabricated by the pulsed laser ablation technique. Superconductivity has been successfully induced in the films after chemical oxidation using sodium hypochlorite solution as oxidizing agent. The structural properties, surface morphology, and electrical resistivity before and after oxidation are compared. In addition, the oxidation mechanism is discussed. PACS 68.55.Jk; 74.76.Bz; 82.40.-g     

Synthesis and optical studies of GdCrO<Subscript>3</Subscript> nanoparticles

Here we report for the first time, a detailed synthesis mechanism of GdCrO₃ nanoparticles using a surfactant-less hydrothermal method. We also report a detailed study of their structural and optical properties. The selected area electron diffraction and powder X-ray diffraction studies of GdCrO₃ nanoparticles show pure phase and excellent crystallinity with average particle size around 50–60 nm. The structural analysis indicates a distorted perovskite crystal structure with lattice parameter values of a = 5.3099 ± 0.0022, b = 5.51793 ± 0.00226, and c = 7.60426 ± 0.00315 Å. For the first time, we report the room temperature UV–vis, photoluminescence, FTIR, and X-ray photoelectron spectroscopy results and their detailed analysis for GdCrO₃. These results provide optical signatures of the formation of GdCrO₃ where both Gd³⁺ and Cr³⁺ play dominant role in different frequency regions.     

Nanoparticles produced by laser ablation of solids in liquid environment

A review of results on nanoparticles formation is presented under laser ablation of Ag, Au, and Ti solids targets in liquid environments (H₂O, C₂H₅OH, C₂H₄Cl₂, etc.). X-ray diffractometry (XRD), UV-Vis optical transmission spectrometry, and high-resolution transmission electron microscopy (HRTEM) characterise the nanoparticles. The morphology of nanoparticles is studied as a function of both laser fluence and nature of the liquid. The evidence of an intermediate phase of Au-Ag alloy is presented under exposure of a mixture of individual nanoparticles to laser radiation. Self-influence of the beam of a femtosecond laser is discussed under the ablation of the Ag target in liquids under Ti:sapphire laser. The factors are discussed that determine the distribution function of particle size under laser ablation. The influence of laser parameters as well as the nature on the liquid on the properties of nanoparticles is elucidated. PACS 42.62.-b; 61.46.+w; 78.66.-w     

Glutathione-capped core-shell structured magnetite nanoparticles: Fabrication and their nonlinear optical characteristics

Core-shell structured magnetic Fe₃O₄@glutathione composite nanoparticles were synthesized and examined using diverse methods including Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscope, thermogravimetric analysis, and vibrating sample magnetometer analysis. In addition, the nonlinear optical measurements were performed by both open and closed aperture z-scan methods using an aqueous colloidal solution of the fabricated nanoparticles. The colloidal system exhibited a positive nonlinear refractive index because of the self-focusing effect arising from optical re-orientation. Although optical re-orientation is a rare phenomenon in nanocolloids, high polarizability of the enveloping organic ligands caused optical re-orientation of the composite nanoparticles in the electrical field direction of the incident beam. Finally, the effect of external voltage on the nonlinear optical index was further investigated.