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Öğe Assessing of Photoluminescence and Structural Properties of Dy+3 doped Cadmium Tantalate Phosphor on the Basis of Charge Balance(2022) Guleryuz, Lutfiye FerayBased on the charge balance, trivalent dysprosium doped Cd1-xTa2 O6:xDy3+ (x=0.5, 1, 2, 3, 5 at%) phosphor series was fabricated by solid state reaction route at 1100 °C for 8 h. The synthesized phosphors were investigated by XRD (X-ray diffraction), SEM (scanning electron microscopy), and PL (photoluminescence) analyses. XRD and SEM analyzes revealed the orthorhombic colombite crystal structure and the presence of oval-like and shapeless morphology with submicron and several micron grain sizes, respectively. With the excitation of 387.8 nm, the phosphors exhibited blue and yellow emissions at 482.4 nm and 578.5 nm depending on the 4F9/2›6H15/2 and 4F9/2›6 H13/2 transitions of Dy3+, respectively. The emission intensity of cadmium tantalate phosphor increased with increasing Dy3+ concentration up to x=5 at% value, and did not occurred the concentration quenching which reduces emission intensity. The reason why concentration quenching did not occur can be attributed to the reduction of structural defects due to the improvement in charge balance and the reduction of the conversion of excitation energy to nonradiative transitions. The Commission Internationale d’Eclairage (CIE) coordinates of Cd1-xTa2O6:xDy3+ (x=0.5, 1, 2, 3, 5 at%) phosphors were found near the white region in the chromaticity diagram.Öğe Boron doping effect on the structural, spectral properties and charge transfer mechanism of orthorhombic tungsten bronze beta-SrTa2O6:Eu3+ phosphor(Royal Soc Chemistry, 2023) Ilhan, Mustafa; Guleryuz, Lutfiye FerayIn the study, the effect of boron doping on spectral properties and CTB mechanism was investigated by using Eu3+ doped orthorhombic beta-SrTa2O6. A phosphor series of Eu3+ doped SrTa2O6, and Eu3+ and B3+ co-doped SrTa2O6 polycrystals were fabricated by solid-state reaction at 1400 degrees C for 20 h in an air atmosphere. The X-ray diffractions of the main phase structure for all the ceramics maintained up to 10 mol% Eu3+ concentration, while the increase of XRD intensity for Eu3+ and B3+ co-doped samples was attributed to somewhat improvement of crystallization. SEM morphologies of grains showed that the presence of boron promotes agglomeration and grain growth. The doping of boron up to 20 mol% led to an increase in PL intensity, CTB energy slightly shifted to low energy, and also an increase occurred in the asymmetry ratio of the phosphor. Therefore, the low crystal field symmetry of the Eu3+ sites and some improvement in crystal structure properties for Eu3+, B3+ co-doped samples supported the PL increase. The trend of Judd-Ofelt parameters (omega(2), omega(4)) is SrTa2O6:xEu(3+), 0.1B(3+) > SrTa2O6:xEu(3+). The high omega(2) parameter for boron co-doped samples showed a covalent Eu-O bond character with low symmetry of Eu3+ environment, while the high omega(4) value indicated the reduction in electron density of the ligands. Some increase in the short decays of Eu3+, B3+ co-doped samples is probably due to the surface effect and low crystal field symmetry. The quantum efficiency of 0.05Eu(3+), 0.1B(3+) co-doped phosphor with the highest PL intensity increased by about 21% compared to that without boron.Öğe Cathodoluminescence and photoluminescence of BaTa2O6:Sm3+ phosphor depending on the sintering temperature(Springer Int Publ Ag, 2022) Ilhan, Mustafa; Guleryuz, Lutfiye FerayThe effect of sintering temperature on the structural and spectroscopic (CL, PL, decay) properties was investigated using 2.5 mol% Sm3+ doped BaTa2O6 samples, which were fabricated by solid state reaction at temperatures of 1150, 1250, 1350, 1425 degrees C. In XRD analysis of Sm3+ doped BaTa2O6 samples, orthorhombic phase appeared at temperatures of 1150 and 1250 degrees C, later the impurity phases disappeared at 1350 degrees C where orthorhombic polymorph completely transformed into a tetragonal tungsten bronze (TTB) structure. SEM analysis revealed the increase of grain size of Sm3+ doped BaTa2O6 with increasing sintering temperature. PL emissions were observed due to (4)G(5/2) -> H-6(J) (J = 5/2, 7/2, 9/2, 11/2, 13/2) transitions of Sm3+ where the emissions increased with the effect of increasing temperature and reached maximum at 1425 degrees C. The increase of PL emissions can be attributed to the developing of the tetragonal phase crystallinity which led to the decrease of non-radiative centers. CL emission of the undoped sample sintered at 1425 degrees C was monitored by the broad blue peak at about 495 nm which is related with the intrinsic emission of BaTa2O6. CL emissions of the doped samples sintered between 1150 and 1425 degrees C showed the host emissions and characteristic emissions of Sm3+ corresponding to (4)G(5/2) -> H-6(5/2), (4)G(5/2) -> H-6(7/2), (4)G(5/2) -> H-6(9/2), (4)G(5/2) -> H-6(11/2) transitions. The Sm3+ concentration led to a decrease in the decay time and an increase in the energy transfer, while the sintering temperature effect showed a different process where the decay time and energy transfer slightly increased.Öğe Characterisation of magnesium matrix composite reinforced with SiC particulates manufactured by powder metallurgy method(Inderscience Enterprises Ltd, 2012) Ozan, Sertan; Guleryuz, Lutfiye Feray; Uzunsoy, Deniz; Ipek, RasimParticle reinforced magnesium metal matrix composites (MMCs) and related manufacturing methods are among important research topics because of their low density, high specific stiffness, strength and wear resistance. SiCp/Mg composites are commonly used materials for fabrication of light-weight functional components. Magnesium powders with mean size of 69 mu m were used as raw material while reinforcement material was selected as SiCp with the average particle size of 84 mu m. Different amounts of SiCp (3, 6, and 9 wt. %) were added to the magnesium matrix and the composite materials were sintered in a vacuum furnace at 590 degrees C. Structural characterisation of the produced composites was performed using several techniques such as scanning electron microscopy (SEM) and X-ray diffraction. The green density of the composite materials increased with SiCp addition. The hardness of the composites was found to be higher than the pure Mg. Reinforcement with 9 wt. % SiCp showed significant increase in the compressive strength of magnesium matrix composites.Öğe A comparison of spectroscopic properties of Dy3+-doped tetragonal tungsten bronze MTa2O6 (M = Sr, Ba, Pb) phosphors based on Judd-Ofelt parameters(Springer, 2022) Ilhan, Mustafa; Keskin, Ilker Cetin; Guleryuz, Lutfiye Feray; Kati, Mehmet IsmailTTB (tetragonal tungsten bronze) crystal structures exhibit very interesting physical properties as well as the superiority of having different cationic sites and allowing doping. In the study, the spectroscopic results of TTB-MTa2O6:Dy3+ (M = Sr, Ba, Pb) phosphors are presented using Judd-Ofelt (JO) intensity parameters. The PL and RL spectra of the phosphors exhibited the characteristic emissions of Dy in the visible and infrared regions. The PL excitation spectra were used to determine JO parameters (omega(2), omega(4), omega(6)). The decreasing trend of omega(2) parameter and PL asymmetry is SrTa2O6:Dy3+ > PbTa2O6:Dy3+ > BaTa2O6:Dy3+, which shows low electronegativity and shifting to the long wavelength of BaTa2O6:Dy3+ supports the low value of the omega(2) parameter and covalence. The PL decay profiles of all the phosphors are double exponential and the fast decreasing of PL decay components of SrTa2O6:Dy3+ is compatible with the concentration quenching after 5 mol%. The decreasing trend of the observed lifetime is in order BaTa2O6:Dy3+ > PbTa2O6:Dy3+ > SrTa2O6:Dy3+, which can be attributed to the defect centers depending on the increase of the covalency.Öğe Evaluation of structural and spectroscopic results of tetragonal tungsten bronze MTa2O6 :Eu3+ (M = Sr, Ba, Pb) phosphors and comparison on the basis of Judd-Ofelt parameters(Elsevier Science Sa, 2022) Ilhan, Mustafa; Kati, Mehmet Ismail; Keskin, Ilker Cetin; Guleryuz, Lutfiye FerayThe crystal structure with different cationic sites and the superiority of allowing doping make TTB (tetragonal tungsten bronze) structures very interesting in terms of exhibiting different physical properties. The new spectroscopic and structural results of MTa2O6:Eu3+ (M = Sr, Ba, Pb) phosphors were presented in the study. The incorporation of europium activator into the different cationic (Sr, Ba, Pb) tunnel structures of TTB crystal with TaO6 octahedral exhibited interesting structural and optical properties. The relationship between coordination number and CTB showed that the highly coordinated A and B sites of TTB crystal caused the CTB to shift to low energy or over 300 nm. The spectral properties of TTB-MTa2O6 :Eu3+ (M = Sr, Ba, Pb) phosphors were compared by determining the Judd-Ofelt (JO) intensity parameters from PL emission spectrum. The (decreasing trend of the Omega(2) parameter and asymmetry ratio is SrTa2O6:Eu3+ > BaTa2O6:Eu3+ > PbTa2O6:Eu3+, and the Eu-O bonds of PbTa2O6:Eu3+ compared to other matrices indicated a more ionic character and a relatively high symmetry environment around Eu3+. The deviation of the experimental (beta(exp)) and Judd-Ofelt (beta(cal)) branching ratios for transition D-5(0)-> F-7(2) are well below 10%, indicating good consistency. All the D-5(0) decay profiles of the phosphors are exponential, and slightly reductions occurred in the luminescence lifetimes for SrTa2O6:Eu3+ and BaTa2O6:Eu3+. XRD results of Eu3+ doped SrTa2O6 series of the high-temperature TTB polymorph reported in this study confirmed the single-phase up to 10 mol%. SEM examinations revealed the change of size and shape of SrTa2O6 samples depending on Eu3+ concentration. (C) 2022 Elsevier B.V. All rights reserved.Öğe Investigation of Dry Sliding Wear Behavior of Mg-SiC Alloys Produced by Powder Metallurgy Method(2022) Aslan, Nail; Yahşi, Yasemin; Guleryuz, Lutfiye Feray; İpek, RasimIn recent years, Mg alloys have great promise for weight-saving applications, because of their superior properties over mo nolithic metals, in the field of automotive and aerospace industries. In this study, the dry sliding wear behavior of Mg- SiC alloys with different sintering temperatures (375°C, 400°C, 425°C) were investigated. Mg with %10 weight SiC powders were mechanically mixed and alloyed and then fabricated successfully via fast heating under vacuumed argon atmosphere. The friction coefficient, hardness value, and wear resistance of the alloys were higher than those of the pure Mg. The increase in the sintering temperature of the Mg-SiC alloys up to 425°C caused an increase in the friction coefficient and a decrease in the wear mass loss respectively.Öğe Investigation of structural, morphological and spectral characteristics of double perovskite Sr2GdTaO6 phosphors doped with Eu3+, and co-doped Eu3+, B3+ having improved quantum efficiency(Springer, 2024) Ilhan, Mustafa; Guleryuz, Lutfiye FerayThe increasing boron effect significantly enhanced the luminescence and asymmetry of double perovskite phosphor. The structural, morphological and spectral characteristics of Sr2Gd1-xTaO6:xEu3+, (x = 0.5-20 mol%) and Sr2Gd1-xTaO6:xEu3+, yB3+ (x = 10 mol%, y = 0-100 mol%) phosphor series were examined in terms of Eu3+ increase and B3+ increase. In XRD results, Eu3+ doped Sr2GdTaO6 samples exhibited a single-phase up to 20 mol%, and slight impurity phase was formed at high concentration in Eu3+, B3+ co-doped Sr2GdTaO6 series. In SEM micrographs, there was no significant change in grain morphology of Eu3+ doped grains, whereas the flux effect of boron led to grain growth in Eu3+, B3+ co-doped samples. The optical band gap energy (Eg) varied in the range of 4.42-4.27 and 4.27-4.08 eV for Eu3+ doped and Eu3+, B3+ co-doped series, respectively. The maximum increases in emissions depending on Eu3+ and B3+ increase were 10 mol% for Sr2GdTaO6:Eu3+ and 50 mol% for Sr2GdTaO6:Eu3+, B3+, respectively. The increased B3+ concentration improved the electric dipole transition (5D0 -> 7F2), and the asymmetry ratio increased from 0.35 to 2.65. Judd-Ofelt (JO) parameters were calculated from the emission spectrum, in which the Omega 2 and Omega 4 parameters for Sr2GdTaO6:Eu3+ phosphors are close values, and both parameters increased in Sr2GdTaO6:Eu3+, B3+. The quantum efficiency of Sr2GdTaO6:Eu3+ phosphors ranged between 49.82 and 93.08%, and the eta QE values for Sr2GdTaO6:Eu3+, B3+ exceeded 100%.Öğe Study on molten salt synthesis, microstructural determination and white light emitting properties of CoNb2O6:Dy3+ phosphor(Elsevier Gmbh, Urban & Fischer Verlag, 2017) Ekmekci, Mete Kaan; Ilhan, Mustafa; Guleryuz, Lutfiye Feray; Mergen, AyhanUndoped, 0.5, 3 and 6 mol% Dy3+ doped CoNb2O6 powders have been prepared by molten salt method using cobalt nitrate hexa hydrate, niobium oxide, dysprosium oxide and Li2SO4-Na2SO4 salt mixture as a flux at 800 degrees C for 4h. X-ray diffraction patterns of the undoped, 0.5 and 3 mol% doped CoNb2O6 samples exhibited a single orthorhombic columbite phase, while 6 mol% Dy3+ doped powder showed minor phase. SEM-EDS results coonfirmed XRD findings and revealed smaller grain size by increasing Dy3+ concentration. Structural and luminescence properties of Dy3+ doped samples in UV-vis spectral region were studied. The emissions increased with increasing doping concentration up to 3 mol%, and then decreased due to concentration quenching effect. The color chromaticity temperature (CCT) data of all samples have been estimated in white light region and color of light appear close to yellowish-green. (C) 2016 Elsevier GmbH. All rights reserved.
