Browsing by Author "Yegingil, Z"

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    Luminescence characteristics of Al-and Ca-doped BeO obtained via a sol-gel method
    Altunal, V; Guckan, V; Ozdemir, A; Can, N; Yegingil, Z
    BeO, BeO:Al-1%, BeO:Ca-1%, and BeO:Al-1%, Ca-0.1% ceramics were synthesized by the sol-gel method. The X-ray luminescence was studied, and broad emission peaks located at 230 nm (similar to 5.4 eV) and 300 nm (similar to 4.1 eV) were observed. We investigated thermoluminescence peaks contributing to optically stimulated luminescence (OSL) signals for the ceramics. The thermal quenching of the OSL signals was evaluated, and the quenching energies were estimated as between approximately 0.5 eV and approximately 0.7 eV. To check the feasibility for dosimetry purposes, the dose response, reusability, and dark storage fading of the OSL signals were investigated. The dose response was observed to be linear between 0.1 and 100 Gy. The minimum detectable doses of BeO, BeO:Al-1%, BeO:Ca-1%, and BeO:Al-1%, Ca-0.1% were estimated as approximately 0.9 mGy, approximately 4 mGy, approximately 0.5 mGy, and approximately 0.5 mGy, respectively. Very good reusability was observed over ten cycles, with a maximum deviation of 2%. The results obtained from BeO:Al-1%, Ca-0.1% could be useful for OSL dosimetry, particularly in medical applications.
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    Characterization and some fundamental features of Optically Stimulated Luminescence measurements of silver activated lithium tetraborate
    Ozdemir, A; Altunal, V; Guckan, V; Can, N; Kurt, K; Yegingil, I; Yegingil, Z
    A new lithium tetraborate (Li2B4O7 or abbreviated as LTB) material was produced by adding various concentrations of Ag impurities to allow better luminescent properties using the solution combustion synthesis (SCS) method. The formation of single phase LTB was confirmed using X-ray Diffraction (XRD) data and Scanning Electron Microscopy (SEM) analysis indicated the existence of a tetragonal crystalline domain. Two broad band emissions located at similar to 272 nm (near UV region) and 526 nm (green region) were observed from room temperature photoluminescence (PL) under 205 nm excitation The synthesized material consisted of polycrystalline LTB with 1 wt% Ag (abbreviated herein as LTB: Ag) exhibits considerable thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) which is several times more sensitive to beta radiation than the other concentrations attempted. It was determined that the OSL signal has been a collection of three component signals. A step-preheating procedure to investigate the depth of the trapping centers associated with the OSL signal was carried out. We suggest that the TL peak at 200 degrees C mainly contributes to the OSL signal. It was observed that the total OSL area shows a linear dose response for beta doses ranging from 1 to 100 Gy. The minimum detectable dose (MDD) value was found to be around 3 mGy using the total OSL area. Under optimum conditions (irradiation with beta-rays), the reproducibility of total OSL area was determined with a - 3% deviation at the end of the 9th irradiation-blue light stimulation-readout cycle. The dark storage stability of the total OSL signals was investigated and fading of the total OSL area was found to be approximately 25% after one week. The trap depth corresponding to the OSL signal was found to be 0.99 eV and 0.94 eV using various heating rate and isothermal annealing methods, respectively. Finally, silver doped lithium tetraborate is shown to have promise as an optically stimulated luminescent dosimeter, particularly in medical and personal applications.
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    Optically Stimulated Luminescence (OSL) dosimetric properties of Li2B4O7:Ag,Gd and its relationship with thermoluminescence (TL) glow-curves
    Ozdemir, A; Can, N; Kurt, K; Yegingil, Z
    The aim of this work was to develop a new lithium tetraborate luminophore with impurities that are strong co-activators for Optically Stimulated Luminescence (OSL) and to investigate its dosimetric properties using OSL method. Li2B4O7:Ag,Gd phosphor consisting of polycrystalline powder was synthesized using Solution Combustion Synthesis method. The structural characterization of the synthesized phosphor was performed using X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) methods. OSL dosimetry properties as a function of step-annealing procedure, radiation dose response, reproducibility of response and loss of stored signal in dark were investigated. Thermoluminescence (TL) glow curve of Li2B4O7:Ag,Gd phosphor consists of two separated glow peaks located at similar to 80 and similar to 210 degrees C with a heating rate of 2 degrees C/s. The traps responsible for these two TL peaks in Li2B4O7:Ag,Gd phosphor were found to be optically sensitive. Li2B4O7:Ag,Gd exhibits high OSL sensitivity and a good OSL signal reproducibility to ionizing radiation. The beta dose-response was performed in the range from 0.1 Gy to 500 Gy. The time-integrated total OSL signal intensity increases linearly with increasing dose from -6 Gy to 500 Gy. The minimum detectable dose was found to be -17.1 +/- 0.9 mu Gy. The stored energy increased -6 % within 4 weeks following a strong fading value of 27 % of the initial OSL intensity after 24 h. Indeed, the X-ray Luminescence (XL) emission spectra are the characteristic of the expected f-f transitions. Luminescence spectrum of Gd doped Li2B4O7 exhibits major red emissions (590 nm, 607 nm, 621 nm) and a weak blue emission (450 nm) along with the emission bands from undoped Li2B4O7. These results strongly suggest that the luminescence properties of Li2B4O7:Ag,Gd deserves more attention as possible dosimeter material. Explanations of many TL/OSL phenomena observed in the study of Li2B4O7:Ag,Gd phosphor and improvements based on the better knowledge in the mechanism of TL/OSL in Li2B4O7:Ag,Gd, a boron-based compound were achieved by this study. (C) 2018 Published by Elsevier B.V.