Browsing by Author "Kelemen, A"

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    Cathodoluminescence and Raman characteristics of CaSO4:Tm3+, Cu phosphor
    Ekdal, E; Guinea, JG; Kelemen, A; Ayvacikli, M; Canimoglu, A; Jorge, A; Karali, T; Can, N
    The physical characterization and phosphor emission spectra are presented for CaSO4 doped with Tm and Cu. All spectral wavelengths are related to electronic transitions of Tm3+ ions. The powder X-ray diffraction pattern showed that the compound exhibits orthorhombic structure and all reflections were indexed without any other secondary impurity phases. Chemical and structural properties of the samples have been characterized by means of Raman spectroscopy and environmental scanning electron microscope (ESEM) with an attached X-ray energy dispersive system (EDS). Group frequencies concept is essential point to the interpretation of the bands due to the main SO4 vibrational units and these displayed main characteristic intensive Raman bands including typical strong intensity at 1016 cm(-1) that corresponds to v(1)SO(4) vibrational mode. From the spatially-resolved cathodoluminescence (CL) spectrum, main emission bands of Tm3+ centered at 346, 362, and 452 nm, due to the respective transitions of P-3(0) -> H-3(4), D-1(2) -> H-3(6), D-1(2) -> F-3(4) were clearly identified. The study is novel as no such CL-ESEM data are available for this doped compound. (C) 2015 Elsevier B.V. All rights reserved.
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    Thermoluminescence characterization of Ag-doped Li2B4O7 single crystal materials
    Kurali, D; Karali, EE; Kelemen, A; Holovey, V; Can, N; Karali, T
    In this study, the thermoluminescence (TL) characteristics of Ag-doped and undoped lithium tetraborate (Li2B4O7, LTB) materials, grown using the Czochralski method, were reported. The TL properties of LTB:Ag, such as glow curve structure, dose response, fading and reproducibility, were investigated. The glow curve of the Li2B4O7:Ag single crystal consists of four peaks located at approximately 75, 130, 190 and 275 degrees C; in undoped LTB, the single crystal shows a broad glow curve with peaks at 65, 90, 125, 160 and 190 degrees C using a heating rate of 5 degrees C/s in the 50-350 degrees C temperature region. The high temperature peak of Ag-doped sample at 275 degrees C has a nonlinear dose response within the range from 33mGy to 9Gy. There is a linear response in the range of 33-800mGy; after which, a sublinear region appears up to 9Gy for Ag-doped LTB single crystal. For undoped single crystal, the dose response is supralinear for low doses and linear for the region between 1 and 9Gy. The thermal fading ratio of the undoped material is almost 60% for the high temperature peak after 7days. Ag-doped LTB single crystal exhibits different behaviour over a period of 7days.