Alkali metal impact on structural and phonon properties of Er3+ and Tm3+ co-doped MY(WO4)2 (M = Li, Na, K) nanocrystals.

The Pechini and microwave-assisted hydrothermal syntheses of nanocrystalline Er3+ and Tm3+ co-doped MY(WO4)2, where M = Li, Na, K, double tungstates are reported. The obtained samples were characterized using standard X-ray powder diffraction (XRD) technique, Rietveld method, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and IR spectroscopy. The smallest crystallites (about 13 nm) could be obtained for the sodium samples synthesized by both the Pechini (for the resin calcined at 550 °C) and hydrothermal methods (synthesis at 230 °C). The average particle size of nanocrystalline powders increases with increasing temperature. It was found that nanocrystals retain the bulk structure with tetragonal and monoclinic symmetry for the sodium and potassium analogues, respectively. In contrast to this behaviour, LiY(WO4)2 undergoes a size-induced structural transformation from monoclinic (space group P2/n) to tetragonal (space group I41/a) symmetry. IR spectra of the synthesized sodium and potassium compounds are very similar to their bulk counterparts. IR spectra of the lithium analogues show, however, abrupt changes when the calcination temperature increases to 850 °C or higher. This behaviour is consistent with the size-induced phase transition in this compound.

Influence of the surface properties on bactericidal and fungicidal activity of magnetron sputtered Ti-Ag and Nb-Ag thin films.

In this study the comparative investigations of structural, surface and bactericidal properties of Ti-Ag and Nb-Ag thin films have been carried out. Ti-Ag and Nb-Ag coatings were deposited on silicon and fused silica substrates by magnetron co-sputtering method using innovative multi-target apparatus. The physicochemical properties of prepared thin films were examined with the aid of X-ray diffraction, grazing incidence X-ray diffraction, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy methods. Moreover, the wettability of the surface was determined. It was found that both, Ti-Ag and Nb-Ag thin films were nanocrystalline. In the case of Ag-Ti film presence of AgTi3 and Ag phases was identified, while in the structure of Nb-Ag only silver occurred in a crystal form. In both cases the average size of crystallites was ca. 11 nm. Moreover, according to scanning electron microscopy and atomic force microscopy investigations the surface of Nb-Ag thin films was covered with Ag-agglomerates, while Ti-Ag surface was smooth and devoid of silver particles. Studies of biological activity of deposited coatings in contact with Bacillus subtilis, Pseudomonas aeruginosa, Enterococcus hirae, Klebisiella pneumoniae, Escherichia coli, Staphylococcus aureus and Candida albicans were performed. It was found that prepared coatings were bactericidal and fungicidal even in a short term-contact, i.e. after 2 h.

Application of effective medium theory with consideration of island shapes to interpret optical properties of discontinuous Pt films.

Pt films with mass thicknesses ranging from 0.6 to 3.9 nm were evaporated onto quartz-glass substrates under vacuum conditions (p ~ 10(-4) Pa) with evaporation rate 0.01 to 0.2 mm/s. The transmittance spectra were measured in the wavelength range from 220 to 2500 nm. The microstructures were examined by a transmission electron microscope. The statistical distributions of island areas and the histograms of the fixed ratios of the semiaxes for ellipsoids were determined. It has been found that the transmittance spectra for the films with coverage coefficient 0.2≤p≤0.6 exhibit minima that shift with an increase in the coverage coefficient. To interpret the transmittance spectra of the films, the Maxwell-Garnett theory, which takes into account the island shapes, was used. Measured and calculated spectra were compared. For low coverage coefficients there is a quantitative agreement between the experimental and the calculated results.

Giant enhancement of upconversion in ultra-small Er³âº/Yb³âº:NaYF4 nanoparticles via laser annealing.

Most of the synthesis routes of lanthanide-doped phosphors involve thermal processing which results in nanocrystallite growth, stabilization of the crystal structure and augmentation of luminescence intensity. It is of great interest to be able to transform the sample in a spatially localized manner, which may lead to many applications like 2D and 3D data storage, anti-counterfeiting protection, novel design bio-sensors and, potentially, to fabrication of metamaterials, 3D photonic crystals or plasmonic devices. Here we demonstrate irreversible spatially confined infrared-laser-induced annealing (LIA) achieved in a thin layer of dried colloidal solution of ultra-small ∼8 nm NaYF4 nanocrystals (NCs) co-doped with 2% Er³âº and 20% Yb³âº ions under a localized tightly focused beam from a continuous wave 976 nm medium power laser diode excitation. The LIA results from self-heating due to non-radiative relaxation accompanying the NIR laser energy upconversion in lanthanide ions. We notice that localized LIA appears at optical power densities as low as 15.5 kW cm⁻² (∼354 ± 29 mW) threshold in spots of 54 ± 3 µm diameter obtained with a 10 × microscope objective. In the course of detailed studies, a complete recrystallization to different phases and giant 2-3 order enhancement in luminescence yield is found. Our results are highly encouraging and let us conclude that the upconverting ultra-small lanthanide-doped nanophosphors are particularly promising for direct laser writing applications.

Microstructural characterization of nanocrystalline gold particles supported on CoCr2O4.

This work presents results of high-resolution transmission electron microscope investigations of microstructure evolution of Au/CoCr(2)O(4) catalyst subjected to various chemical treatments (reduction in hydrogen, reaction of propane oxidation and reaction of CO oxidation). Crystallites of CoCr(2)O(4) support have octahedral or truncated octahedral shape and exhibit well-developed faces, mostly (111). No change in the support morphology was noticed in catalyst samples after various chemical treatments. Small (approximately 8 nm) nanocrystals of gold supported on crystalline CoCr(2)O(4) were observed for the fresh sample. The nanoparticles grow at the surface of CoCr(2)O(4) as thin, disk-like crystallites, in the preferred (111)Au parallel(111)CoCr(2)O(4) epitaxial orientation. Further treatment in hydrogen and in reaction conditions (CO and propane oxidation) did not change noticeably the size of Au particles, but modified slightly their shape. A main reason why Au particles retain small size despite heat treatment is their epitaxial contact with the CoCr(2)O(4) support established during the catalyst preparation.

Structural characterization of nano-sized Ce 0.5 Ln 0.5 O 1.75 (Ln = Yb, Lu) mixed oxides.

This work presents results of HRTEM and XRD studies on microstructure of ceria-based mixed oxides subjected to high-temperature heat treatment in air. Nano-sized (4-5 nm) crystallites of Ce(0.5)Ln(0.5)O(1.75) oxides (Ln = Yb, Lu) with narrow size distribution were prepared by a microemulsion method (W/O). Presence of an intermediate cubic phase, with oxygen vacancy ordering, was found for the Ce(0.5)Ln(0.5)O(1.75) mixed oxides. A simple model of the intermediate phase has been proposed and tested.

Multiferroic BiFeO3 nanoparticles studied by electron spin resonance, X-ray diffraction and transmission electron microscopy methods.

The properties of multiferroic BiFeO3 nanoparticles with core-shell structure produced by mechanically activated room temperature synthesis were studies by electron spin resonance spectroscopy and X-ray diffraction. The data reveal essential differences in ordered and disordered regions among as-prepared and annealed samples. The thermally-induced increase in the average size of the grains and disappearance of the disordered grain shell determined from the electron spin resonance and X-ray diffraction are in a good agreement and were confirmed by transmission electron microscopy observations. Ferro- and ferrimagnetic ordering was observed in as-prepared BiFeO3 nanograins, whereas antiferromagnetic order was apparent in the annealed material. The results show that the electron spin resonance spectroscopy can be considered as an useful method to determine the type of magnetic ordering in multiferroic nanoparticles.

Interfacial reactions and silicate formation in highly dispersed Lu2O3-SiO2 system.

Solid state interface reactions in highly dispersed Lu2O3-SiO2 binary oxide system were studied at 600-1100 degrees C with X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared spectroscopy (FTIR). The results show that at 600-900 degrees C an amorphous, nanometer thick Lu-O-Si layer covering SiO2 particles exists in the system. At higher temperatures the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Lu4[Si3O10][SiO4] silicate, analogue of B-type Dy-Tm disilicates, forms at 1000 degrees C.