Kathriin Utt

Afterglow and thermoluminescence of ZrO2 nanopowders

A careful study of the phosphorescence afterglow and the thermoluminescence (TL) of sol-gel-prepared m-ZrO2 nanocrystalline powders in an extended temperature range −100 to 300 °C was carried out. Wavelength-resolved TL proved the existence of a single active luminescence centre in this temperature range. A TL method based on various heating rates was used to derive more reliable trap depths of 0.75, 0.95, 1.25, 1.46 and 1.66 eV whereas deconvolution methods provided somewhat lower values. The most intense room-temperature afterglows (that were easily observable beyond 1000 s) were obtained from samples annealed at 1250 and 1500 °C, and were attributed mainly to depopulation of the 1.25 eV traps.

TiO2 Nano-Powders as Potential Low-Temperature Optical Gas Sensors

Present work investigates the applicability of nanosized TiO2 (anatase) as a potential optical sensor material for ambient oxygen below room temperature. Titania nanopowders with grain sizes of 10 and 40 nm are prepared via the sol-gel route and tested for the gas response in water deficit conditions. Both powders exhibit sensitivity against oxygen. At-50 °C 40 nm grain size powder remains sensitive to the ambient changes and the PL output increases ~50% whereas 10 nm grain size powders photoluminescence is quenched.

Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate

Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO2 nanoparticles (NPs) on Si substrates. The NPs are bound into the film by p-toluenesulfonic acid (PTSA) and the film is made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon substrate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.

Tailoring Sol-Gel Transition Processes for the Design of Novel Shape Metal Oxide Materials

In present paper we describe some unconventional adaptions of sol-gel method. Controlled sol-gel transformation processes of metal alkoxide based systems can lead to various novel shapes of metal alkoxide materials. Formation of different structures like tubular microstructures by gel sheet rolling, nano- and microfibres by direct drawing, as well as microtubes of metal oxides and gel dispersed liquid crystal materials are described. Different aspects of sol-gel processes leading to the formation of all of these structures are thereby discussed.