Browsing by Author "Kotan, Z"

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    Luminescence and micro-Raman investigations on inclusions of unusual habit in chrysoprase from Turkey
    Ayvacikli, M; Garcia-Guinea, J; Jorge, A; Akalin, I; Kotan, Z; Can, N
    Chemical analyses performed on chrysoprase from Turkey have shown many trace elements as well as rare earth impurities. Quantitative chemical analyses of inclusions in minerals can improve our understanding of the chemistry of surface. The environmental scanning electron microscope (ESEM) with an attached X-ray energy dispersive system (EDS) is capable of producing rapid and accurate major element chemical analyses of individual inclusions in crystals larger than about 30 mu m in diameter. The samples were examined with lifetime-resolved and spatially-resolved cathodoluminescence (CL), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Spatially resolved CL results at room temperature were recorded for two different areas. Bulk area displays with low CL emission and pores contain iron phases such as chromite, hematite and anatase which cause the green color. For the raw data in the lifetime resolved CL spectrum, at least three broad emission bands were detected in a yellow band of the highest intensity at about 550 nm, a weaker orange band at about 650 nm, and a red band at 720 nm. It is assumed that there are links between the CL emissions and the presence of some transition metal and REE elements, but it is obvious that all trace elements do not play a direct role. Micro-Raman measurements were performed on chrysoprase and these showed a characteristic intensive Raman band peaked at 464 cm(-1) which can be inferred to nu(2) doubly symmetric bending mode of [SiO4/M] centers. Raman spectrum of all inclusions found in the material are also given and discussed in detail. (C) 2012 Elsevier B.V. All rights reserved.
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    Solid state synthesis, characterization and optical properties of Tb doped SrSnO3 phosphor
    Kotan, Z; Ayvacikli, M; Karabulut, Y; Garcia-Guinea, J; Tormo, L; Canimoglu, A; Karali, T; Can, N
    In the present study, the structural and optical properties of SrSnO3 doped with Tb ions are reported. Novel SrSnO3:Tb3+ phosphors were conventionally synthesized using a solid state reaction process under a mildly reduced atmosphere (5% H-2 and 95% N-2). The crystal structures, morphologies and optical properties of the resultant materials have been characterised by experimental techniques such as X-ray Diffraction (XRD), Raman spectroscopy (RS), Photoluminescence (PL), Radioluminescence (RL) and Cathodoluminescence coupled to an ESEM (ESEM-CL). The new phosphor material has good crystallization without any impurity phases, which matches with the standard JCPDS files (No. 22-1442) from XRD analysis. The PL, RL and CL measurements taken at room temperature showed that the transitions of D-5(4) to F-7(J) (j = 6, 5, 4, 3) corresponding to the typical 4f -> 4f dipole forbidden intra-configurational transitions of Tb3+ are largely independent of the host material. The green emissions of the D-5(4) -> F-7(5) magnetic dipole transition at similar to 540 nm are predominant for three types of luminescence. PL emission spectra recorded in the temperature range from 10 K to 300 K were influenced by temperature. We report anomalies in the PL spectra of SrSnO3:Tb3+ compatible with a structural phase transition at 260 K while simultaneously exciting and cooling the sample. This work clearly confirms the existence of a phase transition discovered by Singh et al. in SrSnO3 at 270 K. (C) 2013 Elsevier B.V. All rights reserved.
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    Synthesis and Luminescence Properties of Trivalent Rare-Earth Element-Doped Calcium Stannate Phosphors
    Karabulut, Y; Ayvacikli, M; Canimoglu, A; Guinea, JG; Kotan, Z; Ekdal, E; Akyuz, O; Can, N
    The 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.
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    Rare Earth Photoluminescence in Bismuth-Germanate Crystals
    Arslanlar, YT; Kotan, Z; Kibar, R; Canimoglu, A; Can, N
    In the present work, the photoluminescence (PL) spectra of bismuth germanate (BGO) doped with trivalent rare earth element (REE) ions with different doping concentrations (0.03wt% Eu, 0.4wt% Tm, and 1.1wt% Nd) are reported in the temperature range from 10 to 300K using different detectors, namely, photomultiplier tube (PMT), InGaAs (IGA), and Si. The luminescence in the NIR region was also measured at room temperature. Two broad emission bands attributed to undoped BGO were found at circa 1350 and 1800nm, respectively. The broad-band emissions are replaced by narrow-band line emissions defined by the trivalent rare earth dopants. The emission spectra from rare earth ion-doped BGO extend from 500 to 2000nm. Rare earth ions act as the dominant recombination centers and define the emission spectra. This is interpreted as resulting from direct charge transfer from intrinsic defect traps to rare earth recombination centers. The temperature-dependent luminescence of BGO doped with 0.4wt% Tm is also presented.
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    Radioluminescence and photoluminescence characterization of Eu and Tb doped barium stannate phosphor ceramics
    Ayvacikli, M; Canimoglu, A; Karabulut, Y; Kotan, Z; Herval, LKS; de Godoy, MPF; Gobato, YG; Henini, M; Can, N
    In this paper, we report on structural and optical properties of terbium and europium doped barium stannate phosphors (BaSnO3) synthesised by conventional solid state reaction method. We have studied those materials by using X-ray diffraction (XRD), radioluminescence (RL) and photoluminescence (PL) techniques. XRD patterns confirm that the BaSnO3 sintered at 1400 degrees C exhibit orthorhombic structure and that the Tb3+ and Eu3+ substitution of Ba2+ does not change the structure of the BaSnO3 host. The optical emission spectrum is characterized a broad band centered at 897 nm (1.38 eV), with a high-energy tail approximately 750 nm from the host lattice. Other emission signals that are characteristic of the 3 + oxidation state of rare earth elements were generated by Eu and Tb doping. Luminescence measurements show that the series of emission states D-5(4) -> F-7(6), D-5(4) -> F-7(5), D-5(4) -> F-7(4) and D-5(4) -> F-7(3) corresponding to the typical (4)f -> (4)f infra-configuration forbidden transitions of Tb3+ are appeared and the major emission peak at 540 nm is due to D-5(4) -> F-7(5) transitions of Tb3+. On the other hand, the emission spectrum of Eu doped BaSnO3 phosphor exhibits a series of emission bands, which are attributed to the D-5(0) -> F-7(j) (j = 0-4) transitions of Eu3+ ions. The dominant emission of Eu3+ corresponding to the electric dipole transition D-5(0) -> F-7(2) is located at 613 nm. The sharp emission properties exhibited demonstrate that the BaSnO3 is a suitable host for rare-earth ion doped phosphor material. This work clearly confirms the unusual near infrared (NIR) PL discovered by H. Mizoguchi et al. in BaSnO3 at room temperature. (C) 2013 Elsevier B.V. All rights reserved.
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    Solid state synthesis of SrAl2O4:Mn2+ co-doped with Nd3+ phosphor and its optical properties
    Ayvacikli, M; Kotan, Z; Ekdal, E; Karabulut, Y; Canimoglu, A; Guinea, JG; Khatab, A; Henini, M; Can, N
    The 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.
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    Luminescence of dysprosium doped strontium aluminate phosphors by codoping with manganese ion
    Karabulut, Y; Canimoglu, A; Kotan, Z; Akyuz, O; Ekdal, E
    The 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.