Janusz D. Fidelus

Zirconia Based Nanomaterials for Oxygen Sensors - Generation, Characterisation and Optical Properties

Microwave driven hydrothermal synthesis and hydrothermal synthesis were used to obtain ZrO2 nanopowders. Their production with varying phase composition, the characterisation and selected optical properties concerning their potential use as luminescence oxygen sensors are reported. It was found that the powders obtained by the microwave driven hydrothermal method and annealed at 750 0C in air show experiment repeatability within an accuracy of 6 %.

Advanced nanocrystalline ZrO 2 for optical oxygen sensors

It was shown that ZrO2 nanopowders and nanoceramics can be used as an optical oxygen sensor, where the luminescence signal is proportional to the partial oxygen pressure in gases. The nanopowders were obtained in a hydrothermal microwave driven process followed by annealing at 750°C. Nanoceramics were obtained by sintering at pressures up to 6 GPa and at 250°C so that grain growth did not occur. Luminescence of both materials depends linearly on the oxygen content in nitrogen-oxygen mixtures for 2.1% - 25 vol% oxygen content. For luminescence excitation using an electron beam, the luminescence intensity decreases as oxygen pressure increases. For excitation with a laser beam, the opposite effect is observed - the lower the oxygen pressure, the lower the luminescence signal. The experimental results are explained in terms of luminescence centers being distorted lattice sites close to vacancies.

Radiative Decay of Electronic Excitations in ZrO

The time-resolved luminescence was studied for ZrO2:Y single crystal and nanocrystals. The similar recombination centres were found in both single crystal and nanocrystals. Luminescence decay is within 200 ns in nanocrystals, whereas it extends to the microseconds in single crystal. It was shown that the defects responsible for transient absorption were not involved directly in radiative recombination process.

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We report preliminary performance tests of an ORTEC PLS lifetime system based on plastic scintillators and analog electronic system. A variety of samples was measured, from metals (Cu, stainless steel), across semiconductors (Cz-grown silicon, ZnSe) to nanostructured ceramics (ZrO2). All results obtained are compatible with literature reports and indicate the lifetime resolution of the whole system as 180 ps.

Nanocrystals and Macroscopic Single Crystals

Nanoparticles of wide-band-gap materials doped with transition metal ions or rare earth ions are intensively studied for their possible applications in a new generation of light sources for an overhead illumination. In this work we discuss mechanisms of emission enhancement in nanoparticles doped with rare earth or∕and transition metal ions. Arguments are presented that phosphors of nanosize may emit light more efficiently and thus be applied in practical optoelectronic devices.

Testing an Ortec Lifetime System

Pure and Al3+ doped ZnO nanopowders were studied by means of time-resolved luminescence spectroscopy. The powders were synthesized by hydrothermal and plasma methods. These powders were used as a raw material for vaporization-condensation process inside the Solar reactor. The commercially available ZnO nanopowder was studied for a comparison. Exciton to defect band luminescence intensity ratio was estimated in different types of ZnO nanopowders. It was found that nanopowders with whiskers morphology show superlinear luminescence intensity depending on excitation density. The observed effect depends on the average nanoparticle size and on the powder morphology.

Doped nanoparticles for optoelectronics applications

The aim of the work was to examine the influence of pH, high power ultrasound, surfactant and dopant quantity on the particle size distribution of ZrO2:Pr3+, with praseodymium content varying between 0.05 and 10 %. The nanopowders were obtained via a hydrothermal microwave driven process. To establish if the dopant was located on the surface of the zirconia nanoparticles, the particle size distribution, as a function of pH, was measured to obtain an estimate of the isoelectric point of the samples. All results indicated that the dopant was concentrated on the surface: the measurements of the particle size distribution show that the pH corresponding to maximum average particle size changes towards higher values when the Pr content increases. Measurements of the particle size distribution dependency on the application of high power ultrasound and the addition of the sodium dodecyl sulphate surfactant show that, under certain conditions, there is a better stabilisation of the nanopowders in a dispersion and undesirable agglomeration is hindered.

The Luminescence Properties of ZnO nanopowders

Results are presented on the microwave solvothermal synthesis of Co-doped ZnO powders starting from zinc and cobalt acetate precursors in ethylene glycol solutions. The method yields powders with a relatively high degree of agglomeration of initially nucleated nanometer grains. It has been demonstrated that the thermodynamic estimations of the final composition using the Gibbs calculation method are in good agreement with experimental values for the chemical composition in a range of cobalt concentrations up to 15 mol-%

Particle Size Distribution of ZrO2:Pr3+ – Influences of pH, High Power Ultrasound, Surfactant and Dopant Quantity

Sensors based on fiber optics are irreplaceable wherever immunity to strong electro-magnetic fields or safe operation in explosive atmospheres is needed. Furthermore, it is often essential to be able to monitor high temperatures of over 500°C in such environments (e.g. in cooling systems or equipment monitoring in power plants). In order to meet this demand, we have designed and manufactured a fiber optic sensor with which temperatures up to 900°C can be measured. The sensor utilizes multi-core fibers which are recognized as the dedicated medium for telecommunication or shape sensing, but as we show may be also deployed advantageously in new types of fiber optic temperature sensors. The sensor presented in this paper is based on a dual-core microstructured fiber Michelson interferometer. The fiber is characterized by strongly coupled cores, hence it acts as an all-fiber coupler, but with an outer diameter significantly wider than a standard fused biconical taper coupler, which significantly increases the coupling region’s mechanical reliability. Owing to the proposed interferometer imbalance, effective operation and high-sensitivity can be achieved. The presented sensor is designed to be used at high temperatures as a result of the developed low temperature chemical process of metal (copper or gold) coating. The hermetic metal coating can be applied directly to the silica cladding of the fiber or the fiber component. This operation significantly reduces the degradation of sensors due to hydrolysis in uncontrolled atmospheres and high temperatures.

Solvothermal Synthesis of Co-doped ZnO Nanopowders

An novel low-temperature method was used to enhance the corrosion resistance of copper or gold-coated optical fibers. A characterization of the elaborated materials and reports on selected studies such as cyclic temperature tests together with tensile tests is presented. Gold-coated optical fibers are proposed as a component of optical fiber sensors working in oxidizing atmospheres under temperatures exceeding ~900 °C.