Valter Reedo

Spectroscopic and crystal field study of Sm3+ in different phases of TiO2

A systematic study of the photoluminescence spectra of samarium-doped crystalline TiO2 was conducted within the temperature range 10–300 K in order to reveal the energy levels of the trivalent impurity ion in different phases of titania. The sol–gel route was used to prepare Sm-doped TiO2 powders. The nanocrystalline anatase phase was obtained by annealing up to 800 °C, whereas the rutile phase was developed by annealing above 1000 °C. Crystal field calculations of Sm3+ energy levels in the two phases of TiO2 (anatase and rutile) were performed for the first time. The obtained set of energy levels assuming positioning of the Sm3+ ions in regular TiO2 lattice sites was consistent with the experimental results. The effect of the different phases of titania on the impurity is discussed.

Influence of ambient gas on the photoluminescence of sol-gel derived TiO2:Sm3+ films

Photoluminescence (PL) of TiO2:Sm3+ thin films was studied at RT. The films were prepared by the sol-gel spin-coating technique or by atomic layer deposition (ALD) followed by ion implantation. The PL was excited with a Nd:YAG pulse laser emitting at 355 nm. The spectrum of PL consists of intense Sm3+-specific emission lines with a well-pronounced fine structure. The influence of different gaseous environments (air, oxygen, nitrogen) or vacuum on the Sm3+ emission was investigated. In the case of a permanent irradiation of sol-gel films in an oxygen-containing environment, the PL intensity increased. The increase was significantly large but slow. The subsequent evacuation of the measurement chamber led to a rapid decrease of the emission below the detection limit. When the oxygen-containing gas was without any intermediate evacuation replaced by nitrogen, the PL intensity descended to an almost vacuum level. The subsequent exposure to oxygen led to a rather fast emission recovery. The ALD-prepared films exhibited a similar but markedly slower response. The fast response observed was attributed to the adsorption of oxygen on the surface, and the slower one, to the diffusion of oxygen vacancies taking place under the irradiation in the bulk.

Pinching of alkoxide jets—a route for preparing nanometre level sharp oxide fibres

The pinching phenomenon is used to shape jets of Sn(OBu)4 based viscous oligomeric melts into nanometre range sharp oxide needles. The influence of viscosity of the liquid, humidity of surrounding environment and pulling speed on formation of the needles is investigated. Optimal conditions enable reproducible preparation of needles that have tip radii down to 15–25 nm, i.e. in the range that is of considerable interest for many nanotechnological applications.

Micro- and nanoscale structures by sol-gel processing

An overview of the practical output of sol-gel chemistry is demonstrated from the viewpoint of its contribution to the design of 1D and 2D materials. Different structures like thin films, fibres, needles, microtubes, -patterns and -rolls are discussed. In most cases, the advantages of sol-gel processing feasibility and cost-effectiveness are clearly evident. Accompanied by flexibility of production and good quality of the formed structures, the method offers interesting possibilities for practical applications such as sensors, opto-electronic devices, scintillators, etc.

Synthesis of ZrC-TiC Blend by Novel Combination of Sol-Gel Method and Carbothermal Reduction

Titanium Carbide and zirconium carbide binary mixtures (ZrC – TiC) were prepared by sol-gel processing followed by carbothermal reduction. Solution-based synthesis was applied to achieve a molecular dispersion of the reactants. Titanium – (IV) – and zirconium – (IV)butoxides were used as metal sources and hydroquinol was used as carbon source for precursor preparation. Mixture of titanium and zirconium carbides was synthesized by carbothermal reduction at temperatures up to 1500 o C in argon and vacuum environment. The structural transformation of the polymeric materials into the carbides was characterized by SEM, X – ray diffraction analysis and Raman spectroscopy. Characterizations of heat treated samples at 800 o C to 1500 o C in argon and vacuum has showed that the carbothermal reduction of the binary solid carbide mixture (ZrC – TiC) polymeric precursor began in vacuum at lower temperature (1100 o C) than in argon environment.

Simulation of cracking of metal alkoxide gel film formed on viscous precursor layer using a spring-block model

Drying-induced cracking of thin films attached to a non-solid (viscous) substrate is studied both experimentally and numerically. The numerical model is essentially a modification of the spring-block model, introducing a shear stress due to faster drying of the upper film layer, and annealed disorder in the distribution of the spring strengths. The simulation results are in a qualitative agreement with the experimental results, covering all the qualitatively different experimental regimes of the fragment formation. The model allows us to identify the physical processes responsible for the formation of micro-tubes in our experiments, and is helpful in designing and interpreting the film cracking experiments.

Sensitizing of Sm3+ fluorescence by silver dopant in the TiO2 films

Composite material based on a TiO2 matrix doped with Sm3+ ions and co-doped with silver was investigated. Samarium ions together with nano- and micro-aggregates of silver were incorporated into the titanium alkoxide during the sol-gel process. Samarium ions were excited either directly (λexc = 488 nm) or through the TiO2 host (λexc = 355 nm). It was revealed that samarium fluorescence (λexc = 488 nm) in gelled TiO2 films is enhanced by up to 20 times in the vicinity of silver inclusions. Sensitizing and plasmonic mechanisms of enhancement in Sm3+ fluorescence are discussed.

Formation of nickel oxide nanostructures on TiO2

A new method to prepare catalytic NiO templates for growing carbon nanotubes is described. The method utilizes sol-gel chemical reactions in formation of NiO containing nanostructures on TiO2 surfaces. The structures are studied using X-ray photoelectron spectroscopy and atomic force microscopy methods.

Elaboration of hybrid cotton fibers treatedwith an ionogel/carbon nanotube mixtureusing a sol-gel approach

Abstract Ionic liquid (IL) synergy with other materials may influence their properties significantly. Nevertheless, their advantageous liquid state turns out to be an impediment for applications in devices which need stable solid state shaping. In the current study we present a novel method where new siloxane functionalized IL acts as a modifier for carbon nanotubes (CNTs) and titanium alkoxide-CNT coated hybrid cotton fibers. This elaborated route carried out by interconnected and entangled ionic liquid, sol-gel and solid carbon nanotube networks opens up opportunities for functionalization of sol-gel materials with different shapes and sizes. The comparison of properties of IL, ionogel, ionogel/CNT mixture and titanium alkoxide coatings is performed. Ionogel-modified cotton fibers have increased hydrophobicity, linear density, breaking force and ultimate strength as compared to the uncoated cotton fibers. These properties are ensured even after washing threads with water. A uniformly coated CNT network around the fibers strengthens the material and increases its electric conductivity. New type of hybrids can be utilized in formulations which have UV-shielding and hydrophobic properties as well as for antibacterial properties. Characterization studies of the product were carried out by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), optical microscopy and infrared (IR) spectroscopy. Graphical Abstract