Browsing by Author "Derin H."

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    Optical characterization of thin thermal oxide films on copper by ellipsometry
    (2002) Derin H.; Kantarli K.
    A complete optical characterization in the visible region of thin copper oxide films has been performed by ellipsometry. Copper oxide films of various thicknesses were grown on thick copper films by low temperature thermal oxidation at 125 °C in air for different time intervals. The thickness and optical constants of the copper oxide films were determined in the visible region by ellipsometric measurements. It was found that a linear time law is valid for the oxide growth in air at 125 °C. The spectral behaviour of the optical constants and the value of the band gap in the oxide films determined by ellipsometry in this study are in agreement with the behaviour of those of Cu2O, which have been obtained elsewhere through reflectance and transmittance methods. The band gap of copper oxide, determined from the spectral behaviour of the absorption coefficient was about 2 eV, which is the generally accepted value for Cu2O. It was therefore concluded that the oxide composition of the surface film grown on copper is in the form of Cu2O (cuprous oxide). It was also shown that the reflectance spectra of the copper oxide-copper structures exhibit behaviour expected from a single layer antireflection coating of Cu2O on Cu.
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    Spectral, electron microscopic and chemical investigations of gamma-induced purple color zonings in amethyst crystals from the Dursunbey-Balkesir region of Turkey
    (2011) Hatipoǧlu M.; Kibar R.; Çetin A.; Can N.; Helvac C.; Derin H.
    Amethyst crystals on matrix specimens from the Dursunbey-Balkesir region in Turkey have five representative purple color zonings: dark purple, light purple, lilac, orchid, and violet. The purple color zonings have been analyzed with optical absorption spectra in the visible wavelength region, chemical full trace element analyses (inductively coupled plasma-atomic emission spectroscopy and inductively coupled plasma-mass spectroscopy), and scanning electron microscopic images with high magnification. It can be proposed that the production of the purple color in amethyst crystals is due to three dominant absorption bands centered at 375, 530, and 675nm, respectively. In addition, the purple color zonings are also due to four minor absorption bands centered at 435, 480, 620, and 760nm. X-ray diffraction graphics of the investigated amethyst crystals indicate that these crystals are composed of a nearly pure alpha-quartz phase and do not include any moganite silica phase and/or other mineral implications. Trace element analyses of the amethyst crystals show five representative purple color zonings, suggesting that the absorption bands can be mainly attributed to extrinsic defects (chemical impurities). However, another important factor that influences all structural defects in amethyst is likely to be the gamma irradiation that exists during amethyst crystallization and its inclusion in host materials. This gamma irradiation originates from the large underlying intrusive granitoid body in the region of amethyst formation. Irradiation modifies the valence values of the impurity elements in the amethyst crystals. It is observed that the violet-colored amethyst crystals have the most stable and the least reversible coloration when exposed to strong light sources. This situation can be related to the higher impurity content of Fe (2.50ppm), Co (3.1ppm), Ni (38ppm), Cu (17.9ppm), Zn (10ppm), Zr (3.9ppm), and Mo (21.8ppm). © 2011 Taylor & Francis.
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    Preparation and photoluminescence properties of aluminate phosphors produced by combustion synthesis
    (Elsevier Ltd, 2018) Halefoglu Y.Z.; Yüksel M.; Derin H.; Can N.; Topaksu M.; Ozturk E.; Karacaoğlu E.
    In this work, Eu, Nd co-doped MAl2O4:Eu, Nd (M = Ca, Sr, Ba) phosphors were synthesized at low temperatures (550 °C) by the combustion method. The crystallinity of the phosphors was monitored by X-ray diffraction (XRD) and the morphology was examined by scanning electron microscope (SEM). Synthesis of phosphors, the effect of lanthanide concentrations on light emission intensity and duration investigated by using photoluminescence (PL) measurements. Narrow orange-red emissions from 500 to 750 nm in the PL spectra are assigned to 5D0 → 7Fj (j = 0,1,2,3,…) transitions of Eu3+ ion. In contrast, the broad luminescence band of the samples in the range of 400–500 nm are attributed to the 5d-4 f transitions of Eu3+ ion in the same host materials. Investigated the effects of radiation on the severity of the trap depths of these structures. The decay curves of these phosphors show how long the phosphors are attenuated. Thermoluminescence (TL) glow curves have been recorded from room temperature to 300 °C at a constant heating rate of 1 °C/s after preheat process at 130 °C for 10 s using lexsyg smart TL/OSL reader. Nd3+ trap levels can be thought of as the lanthanide element that causes long composition in the phosphorescence structure at room temperature. © 2018 Elsevier Ltd