Marek Jasiorski

Nature and optical behaviour of heavily europium-doped silica glasses obtained by the sol–gel method

Abstract Silica glasses doped with Eu 3+ were prepared by the sol–gel method. The effects of the synthetic procedure on optical properties of the europium heavily doped glasses have been investigated. The fluorescence characteristics of Eu 3+ have been measured for several thermal stages of the sol–gel process. In particular, we have studied aggregation of the Eu ions leading to creation of nanocrystallites during the thermal treatment of silica glasses. The size of the nanocrystalites and their structure have been determined by means of high-resolution transmission electron microscopy and X-ray diffraction. The influence of the OH − groups on the luminescence lifetimes of Eu 3+ has been studied. A broad luminescence band in the blue region has been observed for the silica glasses possessing silanol (Si–OH) groups. Its intensity decreases with the increasing temperature of sintering for the samples treated in the presence of NH 4 Cl. In the case of those heated at high temperatures, doubly doped with Eu and Al silica glasses, a blue emission assigned to the Eu 2+ ions has been observed. Its intensity increases with the Al 3+ ions concentration.

Physicochemical properties of Ru(bpy)32+ entrapped in silicate bulks and fiber thin films prepared by the sol–gel method

Abstract Silicate porous xerogels doped with ruthenium bipyridine (Ru(bpy) 3 2+ ) complex have been obtained in the bulk form and in thin films on optical fibers. The hypsochromic shifts in the absorption and emission maxima are accompanied by fourfold increase in the lifetimes of the entrapped complex. The temperature-dependent lifetimes reveal that silicate xerogels induce two competing thermally activated processes in the excited state decay of the immobilized complex. The excited state lifetimes of the doped bulk xerogels and the fibers coated with thin films containing Ru(bpy) 3 2+ are virtually identical to those obtained for the fibers coated with additional gas-impermeable layers.

Raman Spectra of Molecules Adsorbed on Ag Centers in Sol-Gel Matrices

Silica monoliths and submicron spheres containing silver nanoparticles have been obtained using the sol gel technology. The Ag inclusions were synthesized via the counterdiffusion method. The silver-doped matrices were immersed in solutions of an organic dye (indocyanine green) enabling the solute molecules to interact with surface of the Ag-doped silica matrices. Raman spectra of free solutions of the organic molecules under investigation, the impregnated Ag-doped matrices and the impregnated Ag-free matrices have been measured. The impregnated silica matrices which did not contain silver nanoparticles were used as a reference. These experiments have been performed in order to establish if Raman signal enhancement could be obtained by adsorption of organic molecules on the surface of Ag inclusions in the sol-gel matrices analogously to the standard surface-enhanced Raman spectroscopy (SERS) method.

Spectroscopic and electrochromical properties of metallophthalocyanines in silicate bulks and thin films prepared by the sol–gel method

Abstract Magnesium phthalocyanine (MgPc) and praseodymium bisphthalocyanine (Pr(Pc) 2 ) have been entrapped in bulks and thin films of porous silicate xerogels prepared via the sol–gel method. The electronic absorption data obtained for the complexes immobilized in bulk sol–gel matrices indicate the formation of complex equilibria between their monomeric forms and respective agglomerates. Thin xerogel films doped with metallophthalocyanines and connecting two slides of transparent ITO electrodes display changes in the absorption spectra caused by varying of the applied voltage. These changes appear to be reversible in certain ranges of the applied voltages.

Preparation and Optical Properties of Submicron SiO2 Spheres Doped with YAG:Nd3+ Nanocrystallites

The sol-gel technology has been applied to obtain SiO2 spheres of submicron size. The spheres have been doped with YAG:Nd3+ nanocrystallites. The nanocrystallites have been obtained from aqueous solutions of citric acid, yttrium, aluminum and neodymium chlorides. The obtained gels have been heated up to 800°C. Emission spectra as well as the excited state lifetimes have been measured at room and liquid nitrogen temperatures. The structural characterization has been performed by means of transmission and scanning electron microscopies (TEM, SEM) and powder diffraction (XRD) measurements. We have observed that the YAG:Nd3+ nanocrystallites demonstrate pronounced dependence of the emission intensities on the excitation power as compared to the YAG:Nd3+ crystallites embedded into the submicron SiO2 spheres. The results suggest that silica spheres/YAG:Nd3+ composites are expected to be good hosts for microlaser systems.

Active Sol-Gel Materials

Sol-gel technology has attracted considerable attention due to possibility of obtaining submicron and nano-sized materials. The method of silica and titania nanopowders and thin films obtaining will be presented. Also properties and prospective application of these materials will be express. Additionally, methods of obtaining nanomaterials with different grains shape and specific properties (submicron spherical silica powders, titania nanofibers) will be showed. One of the main advantages of the sol-gel technique is the easiness of doping of the obtained materials with various substances (inorganic, organic, biological). Materials activated this way possess several useful properties. For example, silica spherical matrices with metallic nano-islands on their surface will be presented. Such silver-doped silica powders display anti-microbial capabilities and can be used to obtain doped thin-film coatings e.g. for the production of bacteriostatic textiles. Moreover, materials obtained by the sol-gel method have found wide application in the area of sensors. Examples of optical sensors based on sol-gel derived thin films and optical fiber or planar wave-guide will be also presented.

Aluminium to steel resistance spot welding with cold sprayed interlayer

ABSTRACT Studies on bonding of aluminium alloys to steels are popular because these are structural materials widely used in a variety of industries. However, joining these dissimilar materials is difficult mainly because of the formation of brittle intermetallic compounds. This paper presents a study on welding aluminium to steel by resistance spot welding. Before the welding, steel surface was covered by cold spraying with the layer of aluminium, nickel and nickel–aluminium. This way, instead of the welding of dissimilar materials, the welding of aluminium to aluminium (or nickel) layer pre-deposited on the steel sample was performed. The feasibility of using interlayers for improving the welding of dissimilar materials was tested using SEM, EDX and XRD. Mechanical properties of welds were investigated by microhardness and shear strength tests. The results showed that the coating allowed to decrease hardness in the welding zone and to increase the shear strength of the weld.

Insights into the multistep transformation of titanate nanotubes into nanowires and nanoribbons

Abstract Different types of titanate one-dimensional nanostructured materials were synthesized and characterized using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The results presented in this work unquestionably showed dependence of morphology and structure of the titanate nanopowders on parameters of hydrothermal synthesis. It was found that nanotubes, nanowires and nanoribbons are three unavoidable kinetic products of hydrothermal reaction. Moreover, increasing temperature of reaction or hydrothermal treatment duration results in acceleration of nanotube-nanowire-nanoribbon transformation. However, the sequence of titanate morphology transformation is invariable. The detailed studies further revealed that the crystal structure of hydrothermally prepared nanotubes and nanowires are indistinguishable but the determination of the exact structure is practically impossible. Because of higher crystallinity, the structure of nanoribbons can be established. It was shown that it corresponds to the monoclinic layered trititanic acid H2Ti3O7 and is isostructural with sodium derivatives Na2_xHxTi3O7.nH20 (with x near 2).

Silicate Xerogels with Dopant-Induced Chirality

A series of silicate xerogels with entrapped chiral amino acids have been obtained via sol-gel technology. The transparent, glassy samples obtained exhibit chirality in the bulk due to the presence of the entrapped asymmetric molecules. Measurements of the optical activity of the doped xerogel samples revealed that the entrapment did not significantly influence the optical activity observed for liquid solutions of the amino acids. Thus, the sol-gel method enables the preparation of amorphous optical materials exhibiting properties of strictly spatially defined molecular systems. Apart from the obvious optical applications, such porous materials with asymmetric centers might find interesting applications in chiral chemical syntheses and separations.

Low-Temperature Transformation of Amorphous Sol–Gel TiO2 Powder to Anatase During Cold Spray Deposition

Nanocrystalline TiO2 coatings were successfully deposited on metallic substrate surfaces through low-pressure cold spray. Sol–gel amorphous TiO2 dry gel was for the first time used as a feedstock powder. Agglomerated morphology of the amorphous powder with high-density packing of particles and reduced pores number was an important factor for successful low-pressure cold spraying. However, in the present study one more factor contributing to anchoring of TiO2 particles by cold gas spraying onto a substrate was indicated. This factor enabling effective powder deposition and coating production is based on an exotic for conventional ceramic materials’ plastic deformation of amorphous powder. Furthermore, the detailed analysis of SEM, Raman and XRD measurements clearly demonstrated that amorphous titanium dioxide is transformed into crystalline anatase form during the process of low-pressure cold spraying.