Plasmon-enhanced luminescence of YAG: Yb, Er nanopowders by Ag nanoparticles embedded in silicate glass

Solid-state field-assisted diffusion was used to prepare Ag nano-composite silicate glass. After positive diffusion process, small Ag atoms clusters were formed in the slides. The Ag atom clusters could aggregate into Ag nanoparticles (NPs) with bigger size after subsequent reverse diffusion process. YAG: Yb, Er nanopowders were screen-printed on the glass slides after positive and reverse diffusion, respectively, for up-conversion luminescence measurement. Almost no luminescence enhancement was observed for the slide after positive diffusion. Whereas, obvious enhancement was obtained for the slide after reverse diffusion, and the enhancement factor could reach about 26. The strong enhancement was due to the larger size of Ag NPs. The present work suggested a new promising method to enhance the luminescence of YAG: Yb, Er nanopowders.     

Characterization and optical properties of ZnO nanoparticles obtained by oxidation of Zn nanoparticles

Strong UV emission at about 399 nm (3.1 eV) and multiple blue emissions at 440-490 nm (2.70-2.53 eV) by ZnO nanoparticles have been observed. The characterizations of ZnO nanoparticles, obtained by oxidizing Zn nanoparticles prepared by arc-discharging, were investigated. The multiple blue PL becomes stronger as the oxidation temperature and time increase, which is attributed to the existence of various defects, in particular to interstitial zinc at the surface of the ZnO nanoparticles.     

Thermal activation energy of silver in ion-exchanged soda–lime glass investigated by X-ray photoelectron spectroscopy

The thermal effect on silver in ion-exchanged glasses was investigated in situ by X-ray photoelectron spectroscopy (XPS) in an ultra-high vacuum environment. Each XPS signal of Ag 3d_3/2 and 3d_5/2 consists of two components, the metallic state (Ag⁰) and the oxidized state (Ag⁺), resolved after curve fitting. The toward-surface diffusion of silver was observed by monitoring the changes in concentration on the surface during sample annealing between 20 and 450°C. Judging from the variations in line shape and binding energy and from the enhancement of surface silver under annealing, both metallic and oxidized silver are accumulated on the surface. By applying the diffusion theory in a semi-infinite system to the experimental data, the thermal activation energy of the oxidized silver in ion-exchanged glass, 0.16 eV, was estimated. The activation energy of metallic Ag precipitated during heating, 0.23 eV, was estimated as well.     

Characterization of original and expanded leaf-roots of tobacco by terahertz spectroscopy and X-ray microanalysis

Expanded leaf-roots of tobacco are used as fillers into cigarette products to reduce cost and contents of tar and nicotine and improve quality. To study the difference between expanded and original leaf-roots of tobacco, terahertz (THz) time-domain spectroscopy was used to detect the absorption spectra in the frequency range from 0.2 to 1.5 THz. Significant difference in terahertz absorption was observed in original and expanded leaf-roots. To understand the origin, scanning electron microscope was employed for microanalysis, revealing the difference in element compositions and surface appearances between original and expended leaf-roots. Non-polar and low-polar components of leaf-roots were largely lost after dissolving into liquid CO₂ during expansion, accounting for the difference in THz absorption spectroscopy.     

Upconversion emission of a novel glass ceramic containing Er: BaYF5 nano-crystals

In order to develop highly efficient upconversion (UC) material, Er³⁺-doped oxyfluoride glass ceramics containing BaYF₅ nano-crystals were fabricated for the first time. The randomly distributed BaYF₅ nano-particles with the size of nearly 25 nm precipitated from the glass matrix at about 700 °C, then tended to aggregate slightly with the increase of heating temperature, resulting in the enhancement of Er³⁺ UC emission in the wavelength ranging from 500 nm to 700 nm. The UC process was found very sensitive to Er³⁺ content: with the increase of Er³⁺ content from 0.5% to 1.0%, the UC intensity behaved with drastic exaltation; while further increasing Er³⁺ content to 2.0% resulted in a notable fluorescence quenching. Significantly, the UC efficiency of present glass ceramic preponderates notably over that of the previously reported glass ceramic containing LaF₃, implying its superior UC potentiality.     

Fe@Ag core-shell nanoparticles with both sensitive plasmonic properties and tunable magnetism

Monodisperse Fe@Ag core-shell nanoparticles with relatively uniform Fe cores and Ag shells have been successfully fabricated by a seed mediated method in a two-step reducing process, and then characterized by electron microscopy techniques (HRTEM, EDX), X-ray diffraction (XRD), UV-vis spectroscopy,and magnetometry. The results demonstrate unique optical and magnetic properties for Fe@Ag core-shell nanoparticles. The surface plasmon resonance of Fe@Ag core-shell nanoparticles is red shifted as compared with that of pure colloidal nano-silver, while the plasmon band of Fe@Ag core-shell nanoparticles with thinner Ag shells is shifted to a longer wavelength. Fe@Ag core-shell nanoparticles have a narrow plasmon band and therefore sensitive plasmonic properties. The magnetism of Fe@Ag nanoparticles can be tuned from superparamagnetic to ferromagnetic by modifying the proportion between Fe and Ag contents. The multifunctional Fe@Ag core-shell nanoparticles have potential in optoelectronic, spintronic, and biomedicine applications.     

Synthesis of silver/silica nanocomposites anchored by polymer via in situ reduction

Silver/silica nanocomposites were synthesized by in situ reduction of silver salt and anchorage of the formed silver nanoparticles to silica nanospheres using a polymer anchor. Synthesis conditions including reductants, anchor polymers, and surfactants were determined. The successful formation of the nanocomposites was governed by the reduction of silver nitrate in citrate aqueous solution by sodium borohydride and adsorption onto polyvinylpyrrolidone coated silica nanospheres. The size and structure of the nanocomposites were observed by light scattering measurement and scanning electron microscopy, respectively. Optical properties of the nanocomposites were determined by UV-visible absorption spectra.     

A facile synthetic route to aqueous dispersions of silver nanoparticles

Stable aqueous dispersions of silver nanoparticles have been synthesized from an organometallic precursor dissolved in an organic phase. Hydrogen gas is used to reduce the precursor to form silver nanoparticles which spontaneously transfer into an immiscible aqueous phase where they are stabilized. This route provides a simple pathway for the preparation of aqueous nanoparticle solutions and avoids production of the inorganic ions that are usually associated with aqueous methods. The effectiveness of a variety of aqueous stabilizing agents is evaluated. All products show plasmon absorption bands characteristic of silver nanoparticles and transmission electron microscopy reveals most particles to be below 40 nm in diameter.     

Organic nonlinear optical crystal 4-hydroxy-N-methyl 4-stilbazolium besylate synthesis and characterization

Novel organic nonlinear optical material 4-hydroxy-N-methyl 4-stilbazolium besylate has been synthesized and 7 mm × 5 mm × 3 mm size crystals were grown by slow evaporation technique. Single crystal X-ray diffraction analysis reveals that the crystal lattice is monoclinic. From powder X-ray diffraction analysis the diffraction planes have been indexed. Fourier transform infrared spectrum for our sample confirms the presence of functional groups in the grown crystal. Second harmonic efficiency was determined using Kurtz powder method in comparison with urea to confirm the nonlinearity of the material. The results are discussed in detail.     

Crystallization and characterization of nonlinear optical material l-arginine formomaleate

The influence of mixed acids in the growth and characteristic properties of a new nonlinear optical material l-arginine formomaleate abbreviated as LAFM was examined. Single crystal X-ray diffraction analysis was used to calculate the lattice parameters of the crystals. Fourier transform infrared (FTIR) spectroscopy and thermal analysis (DTA, TGA) were performed to study the molecular vibrations and thermal behaviour of the crystals. UV-VIS spectral study shows that LAFM is transparent down to 315 nm and its second harmonic generation efficiency is 1.2 times that of KDP.     

Use of a chelating agent for the synthesis of high surface area pyrophanite MnTiO3 powders

The effective use of the complexing agent oxine (8-hydroxy quinoline) for the synthesis of high surface area MnTiO₃ powders has been demonstrated. The co-precipitated oxinates yielded carbonates as the decomposed product at 600 °C in flowing nitrogen which on standing for 12 h (at 600 °C) yielded monophasic MnTiO₃. The powders were characterized by PXRD, UV-Visible diffuse reflectance, Raman spectroscopy and BET techniques. PXRD confirmed the rhombohedral symmetry exhibited by MnTiO₃ devoid of any impurities. The surface area of MnTiO₃ was 140 m²/gm. Very broad absorption, typical of charge transfer transition, was observed in the UV/Visible diffuse reflectance spectrum. The Raman spectrum exhibited bands at 221, 252, 327, 349, 437, 600 and 678 cm⁻¹ confirming the symmetry of MnTiO₃. In the TEM images, nanobars, with an average diameter of 20 nm were observed.     

Influence of defects on the quality and optical studies of sodium p-nitrophenolate dihydrate, a nonlinear optical material

Nonlinear optical material of sodium p-nitrophenolate dihydrate was synthesized by employing the technique of controlled evaporation and the effect of temperature on growth morphology was investigated. Single crystal XRD analysis confirms that the crystals with different morphologies have the same lattice parameters. The high-resolution X-ray diffraction curves recorded by a multicrystal X-ray diffractometer revealed the presence of very low angle tilt boundaries. The green emission band at 524 nm is due to the existence of defects on the crystal which corroborated with HRXRD studies. The wide band gap of the SPND crystals confirms the large transmittance in the visible region.     

Synthesis and electrochromic application of surfactants tailored WO3 nanostructures

As WO₃ is excellent material for electrochromic displays more investigation is needed to find the good and low cost method for preparation of WO₃ nanostructures with uniform morphology and narrow distributions using a surfactant mediated method. In this study, the synthesis of WO₃ nanostructures was accomplished using various surfactants such as polyethylene glycol, sodium chloride and sodium dodecyl sulfate and sodium tungstate and diethyl sulfate as the inorganic precursors. All samples were characterized for their opto-structural and morphological studies by UV-Vis spectrophotometer, X-ray diffractometer and scanning electron microscopy techniques. The electrochromic performance of these samples was studied in LiClO₄/PC as electrolyte for Li⁺ insertion/extraction. The use of surfactants has been employed to enhance the uniformity of WO₃ samples.     

Confined growth of Ag2S semiconductor nanocrystals in the presence of PDMAEMA-co-AA polyampholyte co-polymer

Silver sulfide (Ag₂S) nanoparticles were synthesized in the presence of poly(2-(dimethylamino)ethyl methacrylate-co-acrylic acid) co-polymer. It was shown that this polyampholyte can stabilize the growth of the Ag₂S in solution which resulted in formation of nanoparticles with relatively narrow size distribution. The obtained nanoparticles were characterized with structural and optical methods. The results showed that their average size depended on the number of acrylic acid units along the polymer chains.     

X-ray photoelectron spectroscopy (XPS) and FTIR studies of vanadium barium phosphate glasses

Barium vanadophosphate glasses, having composition 50BaO–xV₂O₅–(50 − x)P₂O₅, (x = 0–50 mol%), were prepared by conventional melt quench method. Density, molar volume and glass transition temperature (T_g) were measured as a function of V₂O₅ content. Structural investigation was done using XPS and FTIR spectroscopy. First, substitution of the P₂O₅ by the V₂O₅ in the metaphosphate 50BaO–50P₂O₅ glass increases the density and T_g and decreases the molar volume. When the amount of V₂O₅ increases, all these properties show a reverse trend. XPS measurement found in the O1s, P2p, and V2p core level spectra indicate the presence of primarily P–O–P, P–O–V and V–O–V structural bonds, the asymmetry in the P 2p spectra indeed arises from the spin-orbit splitting of P 2p core level, and more than one valence state of V ions being present. IR spectroscopy reveals the depolymerization of the phosphate glass network by systematic conversion of metaphosphate chains into pyrophosphate groups and then orthophosphate groups. Even though metaphosphate to pyrophosphate conversion is taking place due to breaking of P–O–P linkages, formation of P–O–V and P–O–Ba linkages provide cross linking between short P-structural units, which make the glass network more rigid. Above 10–20 mol% V₂O₅ content, network is highly depolymerized due to the formation of orthophosphate units and V–O–V bridge bonds, resulting in poor cross-linking, making the glass network less rigid.     

Synthesis and luminescence properties of YVO4:Eu nanocrystals grown in nanoporous glass

We report on a feasible method to synthesize luminescence nanocrystals in porous glass in this paper. Well dispersed YVO₄:Eu nanocrystals were proved being grown in nanoporous glass by XRD, micro-Raman spectra and HRTEM equipped with EDS. The YVO₄:Eu³⁺ nanocrystal grown in porous glass herein shows very different luminescence properties compared with single Eu-doped sample. By this method, intense red emission from high silica glass due to energy transfers VO₄³⁻ → Eu³⁺ was obtained. The results show that the reduction from Eu³⁺ to Eu²⁺ in porous glass impregnated with Eu³⁺ ions was avoided effectively.     

Large-scale synthesis of CuS hexaplates in mixed solvents using a solvothermal method

Large-scale covellite CuS hexaplates were successfully synthesized by the 200 °C solvothermal reactions of CuCl₂.2H₂O and (NH₄)₂S in C₂H₅OH-H₂O mixed solvents containing HCOOH as a pH stabilizer, including different amounts and molecular weights (MWs) of polyethylene glycol (PEG). By using XRD and SAED, CuS (hcp) was detected. XRD peaks of the product, synthesized in a solution containing 5 g PEG6000 and 1.5 ml HCOOH for 5 h, are in accordance with those of the simulation and database. The (110) peak shows the preferential growth, corresponding to the hexaplates, characterized using SEM, TEM and HRTEM. CuS hexaplates with the (100) and (010) lattice planes at an angle of 120° were detected on the flat surface, and the (002) lattice plane on the edge. UV-vis absorption edge was detected at 610 nm (2.03 eV), and the PL emission at 361 nm (3.43 eV). Phase and morphology formations were also explained according to the experimental results.     

Synthesis, growth and characterization analysis of nickel mercury thiocyanate crystal (NMTC)

The nonlinear optical single crystal of NiHg(SCN)₄ has been successfully synthesized and good quality single crystal has been grown by slow cooling solution growth technique. The grown single crystals have been analyzed by different characterization analyses in order to know its suitability for various applications. The functional groups have been identified from the FTIR analysis. The TG/DTA analysis reveals the thermal behavior of NMTC. The optical behaviour was assessed by UV–Vis analysis and was found with no absorption in the entire visible region and it may be useful for second harmonic and other relevant applications. The relative second harmonic generation efficiency was evaluated by Kurtz powder technique and was found to be good in comparison with the standard inorganic potassium dihydrogen phosphate.     

Synthesis of Ni nanoparticles by reduction of NiCl2 ionic clusters in the confined space of AOT reversed micelles

Stable Nickel nanoparticles have been synthesized by a novel synthetic route based on the reduction of NiCl₂ ionic clusters in the confined space of reversed micelles. The reaction was carried out by adding anhydrous NaBH₄/ethanol solution to a solution of NiCl₂ ionic clusters nanoencapsulated in bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles in the presence of n-dodecylmercaptane as capping agent. As highlighted by FT-IR, an extraction with water eliminates surfactant and side products leaving lipophilic Nickel nanoparticles to be dispersed in the organic solvent. UV-Vis investigation ascertained the formation of stable metal Nickel nanoparticles exhibiting novel optical properties.     

Structure determination of chitosan-stabilized Pt and Pd based bimetallic nanoparticles by X-ray photoelectron spectroscopy and transmission electron microscopy

Chitosan (CTS)-stabilized bimetallic nanoparticles were prepared at room temperature (rt.) in aqueous solution. Palladium (Pd) and platinum (Pt) were selected as the first metals while iron (Fe) and nickel (Ni) functioned as the second metals. In order to obtain the noble metal core-transition metal shell structures, bimetallic nanoparticles were prepared in a two-step process: the preparation of mono noble metallic (Pd or Pt) nanoparticles and the deposition of transition metals (Fe or Ni) on the surface of the monometallic nanoparticles. The structures of the nanoparticles were studied using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The XPS results show that Pd and Pt exist mainly in zero valences. The presence of Fe and Ni in the bimetallic nanoparticles affects the binding energy of Pd and Pt. Moreover, the studies of O 1s spectra indicate the presence of Fe or Ni shells. The analyses of TEM micrographs give the particle size and size distributions while the high-resolution TEM (HRTEM) micrographs show the existence of noble metal core lattices. The results confirm the formation of noble metal core-transition metal shell structures.