Materials Science Forum Vols. 480-481

Abstract: This paper presents the preparation method, luminescent characteristics and the results of studying the thermoluminescence (TL) properties of zirconium oxide (ZrO2) exposed to 260 nm ultraviolet radiation. The glow curve of ZrO2+PTFE pellets exhibited one peak centered at 180°C about 30°C lower than that the commercially available aluminum oxide peak (Al2O3:C). TL response as a function of spectral irradiance showed good linear in the range from 2.4 to 3000 µJ/cm2 of spectral irradiance. Experimental results of studying the thermoluminescent (TL) properties of ZrO2+PTFE exposed to ultraviolet radiation allow to propose zirconium oxide as an excellent candidate as ultraviolet radiation dosimeter.

Abstract: Various experimental methods are currently employed for the determination of the trap parameters. Methods based on the glow curve shape extract information from a glow peak utilizing the temperature at the maximum emission, TM, the temperature on the ascending part of the peak ,T1, which corresponding to half peak intensity and the temperature on the descending part of the peak, T2, also corresponding to the half peak intensity; as well as, the half width parameters and the symmetry properties. In order to obtain the kinetic order b and the trap parameters, ZrO2 samples were exposed to 260 nm ultraviolet radiation (UVR). The trapping kinetics parameters of the ZrO2 dosimetric peak using the shape of the glow curve were then determined. The order of kinetics followed by the main peak was also determined using the same method. The values of activation energy E and frequency factor ,s, for the main peak of ZrO2 obtained by the above mentioned methods, showed a good agreement among them.

Abstract: X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) were used to investigate the effect of tantalum addition on the TiN thin films structure. Both the HRTEM and selected area electron diffraction have showed that the films possess a fine grained polycrystalline structure with an average grain size in the order of 10 nm. The chemical composition of the films was determined by the use of the Ti2p, N1s and Ta4f core level peaks. The analysis of Ta4f core level revealed the presence of Ta-N bond indicating that tantalum atoms can occupy the titanium sublattice sites. Moreover, the XPS spectra revealed the presence of Ta2O5 in the films.

Abstract: ZnO oxide is a promising material for optoelectronics because of its wide and direct gap (Eg=3.4 eV). Pure and doped zinc oxide powders of various grain sizes have been synthesized by vaporisation-condensation method using a solar furnace. The initial powders contained from 0 to 5 In2O3 mol % . X-ray diffraction technique (XRD) has been used to measure the lattice parameter and the grain size as a function of the composition, the results show the appearance of the spinel phase Zn5In2O8 in the micopowders and the decrease of the grain size of nanopowders as the In concentration increases for all considered compositions. The photoluminescence spectra revealed the presence of two main transitions at 3.31 and 3.36 eV, a shift of the excitonic peaks towards the lower energies, a drastic reduction of the exciton bound to donor emission from the doped material and a large broadening of the excitonic emission in In doped nanopowder.

Abstract: CdZnTe , Cadmium zinc telluride (CZT) is an interesting room temperature radiation detector. This research paper is reporting a negative capacitance behavior of CZT detectors at bias voltages around 60V. Initially at 0V, the CZT capacitance is positive and decreases with bias voltage increase. At around 60V, the measured capacitance approaches zero, then with small voltage increase , capacitance value reverses sign and starts to increase in the negative direction with increasing bias voltage . This effect is stable at 100 kHz. The behavior of low and other quality detectors can differ, low quality detectors can show negative capacitance at low bias voltages and low frequencies. The initial explanation of this phenomena is due to non-uniform distribution of impurities inside the bulk material.

Abstract: The polymorphism and anisotropy of electrical, dielectric, and thermophysical properties of “pure” and doped LiIO3 single crystals are studied. The hexagonal a-LiIO3 phase is a 1-D ionic conductor (along the c axis). The anisotropy of the ionic conductivity of the a-phase can be reduced by doping with transitive metals (Fe, Mo, Ni). The martensitic character of the a«g transition is proved. In the γ-phase, only a slight anisotropy of the conductivity is found. The a«g transition is not an ionic-superionic one.

Abstract: Biological luminescence stimulated by optical excitation results in signals which are characteristic of the host tissue. The spectrum of the emitted light, the intensity, and the excited state lifetimes are modified as the result of disease or by activation through addition of cell selective phosphors. There is an opportunity to identify diseased tissue both by the spectral signals from activators or, in some cases, by the differences of the natural luminescence responses. For practical reasons, defined by the sensitivity range of standard luminescence detectors, much of the current work has focussed on the short wavelength emissions driven by laser activation. However, the techniques are poised to undergo a dramatic expansion in scope with the advent of higher sensitivity photocathodes with high efficiency responses at long wavelengths. It is now possible to utilise a greater range of emission features with improved discrimination. Further, movement to longer wavelength excitation, and emission, open the way to probe deeper beneath the surface of tissue. The current overview will focus on recent examples from detection of cancer to tooth caries and indicate how the non-destructive luminescence probes can distinguish between tissue changes at an early stage of development.

Abstract: The structuring of the inner surface of photocathode windows is of great interest with regard to the efficiency of photomultipliers. A way of increasing the number of photons absorbed by a given surface is to define periodic structures with a period lower or greater than the wavelength of light. Tailoring the structure of the surface to drastically reduce the reflectance, and thus increasing the effective absorption, is possible. Experiments have been conducted with fibre-optic faceplates of imaging tubes. In this work, these structures have been developed by chemical etchants, which selectively react with the transmission fibres or matrix glasses.

Abstract: The dependence of the refractive indices, absorption edge and optical damage in congruent HfO2-doped LiNbO3 crystal are reported. A small amount of Cr3+ ions (0.1 mol%) was introduced in the doped crystals as optical probe. The experimental data indicates that the extraordinary and ordinary indices depend on the Hf4+ ions concentration showing a singularly for a dopant level of ~ 2.7 mol%. The dependence of the absorption edge also shows a transition region at this Hf4+concentration. The distortion of the transmitted light through samples doped with different concentrations of Hf4+ ions indicates that an inhibition of optical damages is achieved at above 3 mol% of dopant. A charge compensation mechanism is proposed to explain the role of the Hf4+ ions for the observed experimental result.

Abstract: In this work, the complete fabrication process which combines Proton Exchange (PE) and Reverse Proton Exchange (RPE) in Neodymium doped LiNbO3 channel waveguides is reported. To produce the PE-RPE channel waveguides the fabrication of dielectric SiO2 masks had to be implemented. For this propose, we adopted a technique based on the Ion Plating Plasma Assisted Deposition of SiO2 followed by the standard ultraviolet photolithographic patterning. On the other hand, we determined the main optical and spectroscopic properties of Nd3+ ions in the channel waveguides including the study of the lifetime as function as the polarisation.