Browsing by Author "Jorge, A"

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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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    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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    Structural and luminescence effects of Ga co-doping on Ce-doped yttrium aluminate based phosphors
    Ayvacikli, M; Canimoglu, A; Muresan, LE; Tudoran, LB; Guinea, JG; Karabulut, Y; Jorge, A; Karali, T; Can, N
    Herein, we primarily focus on luminescence spectrum measurements of various types of green emitting yttrium aluminate phosphors modified with gallium (Y3Al5-xGaxO12) synthesised by solid state reaction. The luminescent emission of samples depends on sample temperature and excitation radiation such as incident X-ray, electron and laser beam. Here, we measured radioluminescence (RL), cathodoluminescence (CL), photoluminescence (PL) along with XRD in order to clarify relationship between lattice defects and the spectral luminescence emissions. The RL and CL spectra of YAG:Ce exhibit an emission band ranging from 300 to 450 nm related to Y-Al antisite defects. The broad emission band of garnet phosphors is shifted from 526 nm to 498 nm with increasing of Ga3+ content, while full width at half maximum (FWHM) of the band tends to be greater than the width of unmodified YAG: Ce garnet. Deconvolution of the spectrum reveals that three emission bands centred at 139, 234 and 294 degrees C occur in aluminate host garnets. (C) 2016 Elsevier B.V. All rights reserved.
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    Characterisation and luminescence studies of Tm and Na doped magnesium borate phosphors
    Ekdal, E; Guinea, JG; Karabulut, Y; Canimoglu, A; Harmansah, C; Jorge, A; Karali, T; Can, N
    In 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.
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    Catholuminescence properties of rare earth doped CaSnO3 phosphor
    Canimoglu, A; Garcia-Guinea, J; Karabulut, Y; Ayvacikli, M; Jorge, A; Can, N
    The present study describes cathodoluminescence (CL) properties of CaSnO3 phosphors doped with Eu3+, Tb3+ and Dy3+ synthesized by a solid-state method. X-ray diffraction (XRD) patterns confirm that CaSnO3 sintered at 1200 degrees C exhibits orthorhombic structure. The evidence and rationale for two strong broad emission bands appeared at 360 and 780 nm for undoped CaSnO3 are presented. The CL measurements exhibit that the 4f-4f emissions from D-5(4) -> F-7(5) (490 nm), D-5(4) -> F-7(5) (544 nm), D-5(4) -> F-7(4) (586 nm) and D-5(4) -> F-7(3) (622 nm), assigned to possible transitions of Tb3+ ions are seen. The strongest one, observed at 544 nm, due to its probability of both magnetic and electric transitions make the sample emission green. Emissions at 480, 574, 662 and 755 nm were detected for the CaSnO3:Dy3+ and attributed to the transitions from the F-4(9/2) to various energy levels H-6(15/2), H-6(13/2), H-6(11/2) and H-6(9/2)+F-6(11/12) of Dy3+, respectively. CL spectra of Eu doped CaSnO3 reveal that there is a strong emission peak appeared at 615 am due to the electric dipole transition D-5(0) -> F-7(2) (red). Finally, our results show that the rare earth doped CaSnO3 have remarkable potential for applications as optical materials since it exhibits efficient and sharp emission due to rare earth ions. (C) 2015 Elsevier Ltd. All rights reserved.