Browsing by Author "Ekdal, E"
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Item Luminescence dating studies of YeAYilova HoyukEkdal, E; Ege, A; Karali, T; Derin, ZCeramic findings collected from YeAYilova Hoyuk located in Izmir were dated using the thermoluminescence dating technique. The area is of significant archaeological importance since it is the first prehistoric settlement in Izmir. Recent archeological observations suggest that human occupation of the region took place about 8500 years ago comparing to previously determined dates of 5000 years. Three samples collected from the same archaeological layer (Neolithic period) in YeAYilova Hoyuk were dated using the thermoluminescence method. Archaeological doses (AD) were obtained by single aliquot regenerative dose method (SAR) for thermoluminescence (TL) using coarse grain quartz minerals extracted from samples. Thick and thin Al2O3:C thermoluminescence dosimeters (TLD) were used to determine the annual dose rate. The archaeological doses were found to vary from 25.91 +/- 0.78 to 26.82 +/- 0.68 Gy, and the annual doses were found to be between 3.34 +/- 0.24 and 3.47 +/- 0.24 mGy/a. The ages obtained for the samples were determined to be 6000 +/- 830 BC, 5740 +/- 670 BC and 5460 +/- 740 years for samples ND1, ND2 and ND3, respectively, which supports the prediction of archeologist that the sampling layer dates from the Neolithic period.Item Thermally stimulated luminescence glow curve structure of β-irradiated CaB4O7:DyAkin, A; Ekdal, E; Arslanlar, YT; Ayvacikli, M; Karali, T; Can, NThermally stimulated luminescence glow curves of CaB4O7:Dy samples after beta-irradiation showed glow peaks at similar to 335, 530 and 675 K, with a heating rate of 2 K/s. The main peak at 530 K was analyzed using the T-max-T-stop method and was found to be composed of at least five overlapping glow peaks. A curve-fitting program was used to perform computerized glow curve deconvolution (CGCD) analysis of the complex peak of the dosimetric material of interest. The kinetic parameters, namely activation energy (E) and frequency factor (s), associated with the main glow peak of CaB4O7:Dy at 520 K were evaluated using peak shape (PS) and isothermal luminescence decay (ILD) methods. In addition, the kinetics was determined to be first order (b = 1) by applying the additive dose method. The activation energies and frequency factors obtained using PS and ILD methods are calculated to be 0.72 and 0.72 eV and 8.76 x 10(5) and 1.44 x 106/s, respectively. Copyright (C) 2014 John Wiley & Sons, Ltd.Item Effect of heating rate on kinetic parameters of β-irradiated Li2B4O7:Cu,Ag,P in TSL measurmentsEge, AT; Ekdal, E; Karali, T; Can, N; Prokic, MThe effect of heating rate on the thermally stimulated luminescence (TSL) emission due to the temperature lag (TLA) between the TSL material and the heating element has been investigated using Li2B4O7:Cu,Ag,P dosimetric materials. The TLA becomes significant when the material is heated at high heating rates. TSL glow curves of Li2B4O7:Cu,Ag,P material showed two main peaks after beta-irradiation. The kinetic parameters, namely activation energy (E) and frequency factor (s) associated with the high temperature main peak of Li2B4O7:Cu,Ag,P were determined using the method of various heating rates (VHR), in which heating rates from 1 to 40 K s(-1) were used. It is assumed that non-ideal heat transfer between the heater and the material may cause significant inconsistency of kinetic parameter values obtained with different methods. The effect of TLA on kinetic parameters of the dosimeter was examined.Item Synthesis and Luminescence Properties of Trivalent Rare-Earth Element-Doped Calcium Stannate PhosphorsKarabulut, Y; Ayvacikli, M; Canimoglu, A; Guinea, JG; Kotan, Z; Ekdal, E; Akyuz, O; Can, NThe phosphors of calcium stannate activated with individual trivalent rare-earth element (REE) ions (Neodymium III, Europium III, Terbium III, Dysprosium III, and Samarium III) were synthesized by high-temperature solid-state reaction (SSR), and their characterization and luminescent properties were investigated. The crystal structures and morphologies of the resultant materials were well characterized by experimental techniques such as X-ray powder diffraction (XRD) and environmental scanning electron microscopy (ESEM). The XRD results display that the rare-earths substitution of Calcium II does not change the structure of calcium stannate host. Obviously, the ESEM image exhibits that phosphors aggregate and their particles with irregular shape exist. The calcined powders of the Europium III, Neodymium III, Samarium III, Dysprosium III, and Terbium III ions doped in calcium stannate exhibits bright red, reddish orange, yellowish, orange white, and green light, respectively. Although there is some intrinsic emission ranging from UV to near-infrared (NIR) due to the host lattice, the dominant signals are from the rare-earth sites, with signals characteristic of the trivalent rare-earth states. The emission spectrum from undoped-calcium stannate phosphor is characterized by two broad bands centered at similar to 800 and similar to 950nm. The shapes of the emission bands are different for each dopant. The sharp emission properties show that the calcium stannate is a suitable host for rare-earth ion-doped phosphor material. Furthermore the influence of different rare-earth dopants, that is, Europium III, Neodymium III, Samarium III, Dysprosium III, and Terbium III, on thermally stimulated luminescence (TSL) of calcium stannate phosphor under the beta irradiation was discussed. Among these trivalent rare-earth-doped phosphors samarium-doped material showed maximum TSL sensitivity with favorable glow curve shape.Item Radioluminescence study of rare earth doped some yttrium based phosphorsAyvacikli, M; Ege, A; Ekdal, E; Popovici, EJ; Can, NThis paper reports the luminescence emission spectra of Y(Ta,Nb)04 activated by rare earth ions such as Eu3+ and Tb3+. The influence of these rare earth ions on the radioluminescence (RL) of yttrium niobate and tantalate phosphors was investigated. The luminescent properties were studied under X-ray and preliminary RL measurements to further evaluate prepared materials. The emission centers of the rare earth activators (Eu3+, Tb3+) were found to contribute efficiently to the total luminescence. With their various luminescence chromaticities, these rare earth activated phosphors are promising materials for solid-state lighting applications as well as for X-ray intensifying screens in medical diagnosis, providing the broad band variation of visible RL from blue to red. (c) 2012 Elsevier B.V. All rights reserved.Item Cathodoluminescence and Raman characteristics of CaSO4:Tm3+, Cu phosphorEkdal, E; Guinea, JG; Kelemen, A; Ayvacikli, M; Canimoglu, A; Jorge, A; Karali, T; Can, NThe 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.Item Solid state synthesis of SrAl2O4:Mn2+ co-doped with Nd3+ phosphor and its optical propertiesAyvacikli, M; Kotan, Z; Ekdal, E; Karabulut, Y; Canimoglu, A; Guinea, JG; Khatab, A; Henini, M; Can, NThe optical properties of alkaline earth aluminates doped with rare earth ions have received much attention in the last years and this is due to. their chemical stability, long-afterglow (LAG) phosphorescence and high quantum efficiency. However, there is a lack of understanding about the nature of the rare earth ion trapping sites and the mechanisms which could activate and improve the emission centers in these materials. Therefore a new phosphor material composition, SrAl2O4:Mn2+, co-doped with Nd3+ was synthesized by a traditional solid-state reaction method. The influence of transition metal and rare earth doping on crystal structure and its luminescence properties have been investigated by using X-ray diffraction (XRD), Raman scattering, Photoluminescence (PL) and Radioluminescence (RL). Analysis of the related diffraction patterns has revealed a major phase characteristic of the monoclinic SrAl2O4 compound. Small amounts of the dopants MnCO3 and Nd2O3 have almost no effect on the crsytalline phase composition. Characteristic absorption bands from Nd3+ 4f-4f transitions in the spectra can be assigned to the transitions from the ground state I-4(9/2) to the excited states. The luminescence of Mn2+ activated SrAl2O4 exhibits a broad green emission band from the synthesized phosphor particles under different excitation sources. This corresponds to the spin-forbidden transition of the d-orbital electron associated with the Mn2+ ion. In photo- and radio-luminescence spectra, Nd3+ 4f-4f transition peaks were observed. The emitted radiations for different luminescence techniques were dominated by 560, 870, 1057 and 1335 nm peaks in the visible and NIR regions as a result of I-4(9/2) -> (4)G(7/2) and F-4(3/2) -> I-4(J) (J=9/2, 11/2 and 13/2) transitions of Nd3+ ions, respectively. Multiple emission lines observed at each of these techniques are due to the crystal field splitting of the ground state of the emitting ions. The nature of the emission lines is discussed. (C) 2013 Elsevier B.V. All rights reserved.Item Characterisation and luminescence studies of Tm and Na doped magnesium borate phosphorsEkdal, E; Guinea, JG; Karabulut, Y; Canimoglu, A; Harmansah, C; Jorge, A; Karali, T; Can, NIn this study, structural and luminescence properties of magnesium borate of the form MgB4O7 doped with Tm and Na were investigated by X-ray diffraction (XRD), Raman spectroscopy and cathodoluminescence (CL). The morphologies of the synthetised compounds exhibit clustered granules and road-like materials. As doping trivalent ions into a host with divalent cations requires charge compensation, this effect is discussed. The CL spectra of undoped MgB4O7 shows a broad band emission centred around 350 nm which is postulated to be produced by self-trapped excitons and some other defects. From the CL emission spectrum, main emission bands centred at 360, 455, 475 nm due to the respective transitions of D-1(2)-> H-3(6),D-1(2)-> F-3(4) and (1)G(4)-> H-3(6) suggest the presence of Tm3+ ion in MgB4O7 lattice site. CL mechanism was proposed to explain the observed phenomena which are valuable in possibility of the developing new luminescent materials for different applications. In addition, the experimental Raman spectrum of doped and undoped MgB4O7 were reported and discussed. (C) 2015 Elsevier Ltd. All rights reserved.Item Study of luminescence of Mn-doped CaB4O7 prepared by wet chemical methodOguz, KF; Ekdal, E; Aslani, MAA; Canimoglu, A; Guinea, JG; Can, N; Karali, TIn this study, manganese (Mn) doped Calcium Tetraborate (CaB4O7) samples were prepared by the wet chemical method. Under beta irradiated, CaB4O7:Mn showed thermally stimulated luminescence (TSL) glow peaks at approximately 85 degrees C and 220 degrees C with a heating rate of 5 degrees C/s. Peak shape (PS) and various heating rates (VHR) methods were applied for determining the trap parameters such as order of kinetic (b), activation energy (E) and frequency factor (s). The results indicate that the main dosimetric peak of CaB4O7:Mn follows the second-order kinetic model. The thermal fading ratio of the material is around 15% at the end of one month period of storage. The results of the TL studies carried out on the CaB4O7:Mn dosimeter revealed that it has high sensitivity, which makes it very valuable in various dosimetric applications like space, medical, personal dosimetry and dating. Radioluminescence (RL) of CaB4O7:Mn was also studied. It is shown that the RL spectrum contains a wide band centered at 530 nm assigned to Mn2+ ion emission. A broad band emission feature peaked at 350 nm assigned to the non-bridging oxygen hole center (NBOHC) is also discussed and a model is proposed to explain this broad band feature. (C) 2016 Elsevier B.V. All rights reserved.Item Thermoluminescence studies of Nd doped Bi4Ge3O12 crystals irradiated by UV and beta sourcesKarabulut, Y; Canimoglu, A; Ekdal, E; Ayvacikli, M; Can, N; Karali, TThermoluminescence (TL) glow curves of pure and rare earth doped bismuth germanate (BGO) were investigated under UV and beta radiation. The glow curves of pure BGO crystal present different patterns for both kinds of radiation. The TL glow curves of BGO crystals doped with Nd ions are similar to that of pure BGO under UV radiation. The kinetic parameters, kinetic order (b), activation energy (E) and frequency factor (s) of the TL glow curves of pure BGO crystal have been determined by peak shape method. Activation energies of 3 peaks obtained by PS were found to be 1.81, 1.15 and 1.78, respectively. (C) 2016 Elsevier Ltd. All rights reserved.Item Luminescence of dysprosium doped strontium aluminate phosphors by codoping with manganese ionKarabulut, Y; Canimoglu, A; Kotan, Z; Akyuz, O; Ekdal, EThe authors report here the luminescence properties of strontium aluminate doped with dysprosium and manganese. The dysprosium, manganese co-doped powders were prepared by a solid state reaction at temperatures at 1600 degrees C under H-2 (15%)-Ar (85%) atmosphere. The dysprosium, manganese co-doped strontium aluminate phosphors have the monoclinic structure with lattice parameters a approximate to 8.440 angstrom, b approximate to 8.821 angstrom, c approximate to 5.157 angstrom and beta approximate to 93.4 degrees. The characteristic (4)F9/2 -> H-6(15/2) (blue), F-4(9/2) -> H-6(13/2) (yellow), F-4(9/2) -> H-6(11/2) (red) and F-4(9/2) -> H-6(9/2) (NIR) transitions of Dy3+ for different luminescence techniques (radioluminescence, photoluminescence and cathodoluminescence) were detected in the emission spectra at the room temperature. The luminescence of Mn2+ co-doped SrAl2O4:Dy3+ exhibits a broad greenorange emission band (T-4(1) -> (6)A(1) transition) from the synthesized phosphor particles under different excitation sources. This corresponds to the spin-forbidden transition of the d-orbital electron associated with the Mn2+ ion. Multiple emission lines observed at each of these techniques are due to the crystal field splitting of the ground state of the emitting ions. The nature of the emission lines is discussed. (C) 2013 Elsevier B.V. All rights reserved.Item Determination of thermoluminescence kinetic parameters of Li2B4O7:Cu, Ag, PEge, A; Ekdal, E; Karali, T; Can, NThe kinetic parameters of a newly prepared tissue-equivalent, highly sensitive thermoluminescent detector, Li2B4O7: Cu, Ag, P of sintered pellets have been calculated. Thermoluminescence (TL) glow curves of Li2B4O7: Cu, Ag, P samples after beta-irradiation showed peaks at about 384 and 446 K with a heating rate of I K s(-1). The kinetic parameters, namely activation energy (E) and frequency factor (s) associated with the main glow peak (446 K) of Li2B4O7: Cu, Ag, P have been determined using isothermal decay (ID) and peak shape (PS) methods. The activation energies obtained by ID and PS methods are calculated to be 1.12 and 1.13eV (mean), respectively. The frequency factors obtained by both methods are 7.61 x 1011 and 3.53 x 1011 s(-1) (mean), respectively. Results obtained using both methods are compared and discussed. (c) 2007 Elsevier Ltd. All rights reserved.