Browsing by Author "Kati, MI"
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Item Effects of CdS quantum dot in polymer nanocomposites: In terms of luminescence, optic, and thermal resultsKeskin, IÇ; Türemis, M; Kati, MI; Kibar, R; Çetin, ACdS quantum dots (QDs) which have unique luminescence efficiency were synthesized by two-phase method using oleic acid (OA) as a surfactant. The nanocomposites have been obtained by blended CdS quantum dots with low-density polyethylene (LDPE) in different ratios. Primarily, radioluminescence (RL) properties were investigated as well as their structural (FT-IR, XRD), morphological (TEM, SEM), thermal (TG-DTA) and absorption (UV-Vis) properties of these nanocomposites. The RL peaks of OA-capped CdS QD were observed at 456 nm and 655 nm. As a consequence of the nanocomposites being doped with powder CdS QD, a significant blue shift was observed in the absorption bands. The optical band gap of CdS was calculated as- 2.3 eV. The nanocomposites blended with CdS QD, this value increased to- 2.7 eV. It has also been observed that nano particles cause nanocomposites to have lower melting temperatures.Item Influence of Boron Doping on the Dielectric Characteristics of Eu3+-Doped β-SrTa2O6 and Eu3+-Doped BaTa2O6 Tungsten Bronze-Type CeramicsIlhan, M; Kati, MI; Sahin, N; Esmer, KThe effect of boron doping on dielectric properties was examined using beta-SrTa2O6:xEu(3+) (x = 1.5 mol%, 3 mol%, 5 mol%, 10 mol%), beta-SrTa2O6:xEu(3+), yB(3+) (x = 1.5 mol%, 3 mol%, 5 mol%, 10 mol%, y = 10 mol%) and BaTa2O6:xEu(3+), yB(3+) (x = 10 mol%, y = 0 mol%, 5 mol%, 15 mol%, 30 mol%, 50 mol%, 70 mol%, 100 mol%) tungsten bronze ceramics produced by the solid-state reaction method. X-ray diffraction (XRD ) results of all the beta-SrTa2O6 and BaTa2O6 samples showed that they retained a single-phase structure. In scanning electron microscopy (SEM) examinations, the presence of boron promoted grain growth and agglomeration in the beta-SrTa2O6 grains, while the increased boron concentration led to grain elongation in addition to grain growth in the BaTa2O6 grains. The dielectric results for the beta-SrTa2O6:xEu(3+) and beta-SrTa2O6:xEu(3+), yB(3+) series showed that increased Eu3+ caused a decrease in the dielectric constant (epsilon ') and dielectric loss (tan delta), whereas the increasing B3+ presence for the BaTa2O6:xEu(3+), yB(3+) series led to an increase in the dielectric constant and a decrease in dielectric loss. The increase in tetragonality for BaTa2O6:xEu(3+), yB(3+) ceramics was correlated with a higher ferroelectric Curie temperature.Item Luminescence characteristics and kinetic parameters of LiBaPO4: Tb3+, Dy3+phosphors synthesized by sol-gel methodKati, MI; Gökce, S; Keskin, IÇ; Türemis, M; Çetin, A; Kibar, RLiBaPO4: Tb3+, Dy3+ phosphors were prepared via sol-gel method by using the stoichiometric amounts of lithium nitrate LiNO3, barium nitrate Ba(NO3)2 and ammonium dihydrogen phosphate NH4H2PO4 as base materials. Morphology by scanning electron microscopy (SEM), structure by X-ray diffraction (XRD), thermal properties by Differential thermal analysis (DTA)/Thermogravimetric Analysis (TGA) and structural characteristics by Fourier transform infrared spectroscopy (FT-IR) were investigated. This paper presents luminescence properties using spectra from radioluminescence (RL), photoluminescence (PL), cathodoluminescence (CL) and, thermoluminescence (TL) and the influence of RE dopants (Tb3+, Dy3+) on the luminescent behavior of LiBaPO4. Computerized Glow Curve Deconvolution (CGCD) and Peak Shape Method were used to determine the kinetic parameters and the obtained results were evaluated. The RL results of un-doped LiBaPO4 showed the presence of a well-defined peak at 417 nm and a weaker band around 685 nm. Strong emissions were detected in the sample doped with Dy3+ correspond to 4F9/2 -> 6Hj transitions. Blue, yellow and red emissions were observed with transitions of 4F9/2 -> 6H15/2, 4F9/2 -> 6H13/2 and 4F9/2 -> 6H11/2, respectively. As for LiBaPO4: Tb3+, green emissions originated from the characteristic transitions (5D3 -> 7FJ (j = 6-3) and 5D4 -> 7FJ (j = 6-1)) of Tb+3 ion was seen. The RL, PL and CL spectra were identical, suggesting these green emissions. Dy3+ doped sample has three glow curves located at 72 degrees C, 145 degrees C and 204 degrees C, while the main temperature peak is measured at 240 degrees C for Tb3+ doped sample. Chromotographic studies of LiBa0 & sdot;98PO4: Dy3+0.02 reveals that calculated x and y color coordinates (0.3122, 0.3233) are very close to the white light.Item Comprehensive study on structural, thermal, morphological and luminescence (RL, PL, TL) properties of CaLa2(WO4)4: Tb3+, Dy3+ phosphors synthesized via sol-gel methodTüremis, M; Keskin, IÇ; Kati, MI; Çetin, A; Ay, K; Kibar, RTb3+/Dy3+ co-doped CaLa2(WO4)(4) (CLW: Tb3+/Dy3+) and its derivatives were synthesized by the sol-gel method. The morphology, thermal, structure and luminescent-optical properties the as-prepared light-emitting phosphors were characterized by utilizing scanning electron microscopy (SEM), differential thermal analysis (DTA)-thermogravimetric analysis (TG), X-ray diffraction (XRD) and radioluminescence (RL or X-ray luminescence) photoluminescence (PL) -thermoluminescence (TL or TSL) - optical absorption spectrometry. The Tb3+ and Dy3+ ions were singly or doubly doped and the results were examined in detail. Moreover, for these phosphors, the energy transfer mechanisms which depend on RL and PL spectra were determined. The samples excited by X-ray demonstrate characteristic luminescence peaks of Dy3+ (422, 480, 575, 663 and 747 nm) and Tb3+ (489, 544, 586, 620, 652 and 675 nm). These emissions are similar for RL and PL measurements. It could be said that the energy transfer efficiency of the host material is perfect for rare-earth ions. The synthesized phosphors exhibit various colors from yellow to blue under UV excitation. The optical band gaps of host CLW, CLW: Tb3(+), CLW: Dy3+ and co-doped CLW: Tb3+/Dy3+ were calculated at values 3.83 eV, 3.44 eV, 3.64 eV and 3.52 eV, respectively. From the results obtained, the CaLa2(WO4)(4): Tb3+, Dy(3+)phosphors may be one of the potential candidates for light-emitting diode.Item The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dotKeskin, IÇ; Türemis, M; Kati, MI; Kibar, R; Sirin, K; Çipiloglu, MA; Kus, M; Büyükcelebi, S; Çetin, AIn this work, highly luminescent alloyed CdSeS QDs are successfully synthesized by two phase route method by using oleic acid (OA) as a surfactant. OA capped CdSeS QDs prepared in two different synthesis duration were compared in terms of luminescence and optical properties. The nanocomposites blended with CdSeS QDs which have highly luminescent efficiency in different ratios by Low Density Polyethylene (LDPE) and these nanocomposites were mainly investigated radioluminescence (RL) and optical properties (UV/VIS absorption). Structural, morphological, thermal properties of the nanocrystal and nanocomposites were examined using; XRD, FT-IR, TEM, SEM, TG-DTA techniques. OA capped CdSeS and also nanocomposites were showed two RL spectrum peaks in green and red region at around 528 nm and 710 nm respectively. Also, it is seen that the radioluminescence intensity changes linearly with the particle size of the QDs and about 12% size change of quantum dot led to a threefold increase in RL intensity. The luminescence glow curves are in compliance with absorption and fluorescence spectra. The absorption bands showed a significant blue shift for the nanocomposites as compare to powder CdSeS. The optical band gap of the OA capped CdSeS calculated as 1.77 eV. It was observed that the optical band gap of LDPE was decreased by the adding ratio of CdSeS from 3.71 eV to 2.25 eV. (C) 2017 Elsevier B.V. All rights reserved.Item X-ray irradiated thermo- and radioluminescence, structural and thermal characterization of septarian (powder&bulk) from MadagascarKeskin, IÇ; Kati, MI; Türemis, M; Gültekin, S; Üstün, S; Çetin, A; Kibar, RThe luminescence properties of septarian have been investigated for the first time in this study, which has been the subject of many studies in both geological and geophysical fields. This sediment with a calcium carbonate structure exhibited high luminescence properties with X-ray excitation. The radioluminescence (RL) and thermoluminescence (TL) properties were investigated as well as their structural (FT-IR, XRD), morphological (SEM), thermal (TG-DTA) and absorption (UV-Vis-NIR) properties of this sediment. The broad RL peak of septarian was observed at 640 nm. There was a significant increase in the RL intensities of the sifted samples compared with the bulk sample. The TL glow curves of septarian irradiated with X-rays exhibited intense main TL glow peak having the maximum temperatures at 116 degrees C and about 390 degrees C with a heating rate of 2 degrees C/s. Also; the TL kinetic parameters were reported; activation energy (E), frequency factor (s) and the order of kinetics (b) of the first peak have been determined in detail by using peak shape (PS) and Computerized Glow Curve Deconvolution (CGCD) methods. SEM and EDS analysis were performed for the two different layers of septarian. The light colored side with the amorphous structure of the sample has more impurities (such as Fe, Al, Zr, K) than the crystallized and darker side.Item Optimizing Optical and Structural Properties of Nanocomposites by ZnO and BP-3Türemis, M; Keskin, IÇ; Kati, MI; Kibar, R; Sirin, K; Çanli, M; Çorumlu, V; Çetin, AThis study aims to find out usage of zinc oxide (ZnO) and 2-hydroxy-4-methoxybenzophenone (BP-3) for getting better optical and structural properties of nanocomposites. Polymer nanocomposites were prepared by adding zinc oxide for minimizing UV rays effects of the sun with the particle size of nanometer in different ratios to a low density polyethylene (LDPE). The polymer mixtures were synthesized by mixing nanocomposite samples with BP-3 featuring UV stabilizer. Besides making tensile testing measurements, in order to find out the optical, structural, mechanical and thermal changes, the new polymer nanocomposites were characterized by XRD, TG-DTA spectra, and SEM images. The samples with zinc oxide which show luminescent properties were examined in terms of radioluminescence features. Radioluminescence spectrum showed characteristic peaks of zinc oxide dispersed nanocomposites prepared with LDPE. The intensity of the characteristic peaks at 530 and 390 nm (exciton) increased by increasing rates of nanopowder zinc oxide while adding BP-3 to the composites caused a decrease in intensity of radioluminescence.Item Structural and optical properties of SrAl2O4: Eu2+/Dy3+ phosphors synthesized by flame spray pyrolysis techniqueGültekin, S; Yildirim, S; Yilmaz, O; Keskin, IÇ; Kati, MI; Çelik, EIn this study Sr0.985Al2O4:0.005Eu(2+)/0.01Dy(3+) luminescent materials with long afterglow and high intensity were synthesized by flame spray pyrolysis (FSP) method for the first time. Precursor solution was divided into two separate part. One of the parts was used FSP process, the other one was dried to simulate sol- gel process. Thermal properties and organic content of FSP derived particles and dried gel were compared using DTA-TG and FTIR devices. FSP derived particles were sintered in argon medium at 1200 degrees C. Phase and elemental analysis of the final phosphors were carried out by X-Ray Diffraction (XRD) and X-Ray Photo electron Spectroscopy (XPS) measurements. Scanning electron microscopy (SEM) images were obtained to observe particle morphology. Optical properties of phosphor were determined by Photoluminescence (PL), thermoluminescence (TL) and radioluminescence (RL) measurements. The emission spectra of Sr0.985Al2O4: 0.005Eu(2+)/0.01Dy(3+) were composed by a green band at 525 nm at room temperature when it was excited by 350 nm light, assigned to anomalous luminescence originated by Eu2+ and Dy3+ in the host lattice. There were estimated peaks at around 90, 130, 170 and 200 degrees C under the main glow curve in the sample irradiated by X- ray and He- Ne laser (lambda(exc) = 632 nm). RL spectrum of Sr0.985Al2O4 : 0.005Eu(2+)/0.01Dy(3+) powders have four distinct emission peaks at around 527 nm, 576 nm, 667 nm, 753; nm and a comparatively weak emission band at about 846 nm.Item Characterization and determination of thermal and radioluminescence properties of low-density polyethylene (LDPE)-(nanozeolite + Y2O3) compositeÇanli, M; Keskin, IÇ; Türemis, M; Sirin, K; Kati, MINanotechnology has become one of the most popular areas of interdisciplinary research. In the vast majority of nanotechnology applications, polymer-based matrices were used as the dispersing medium of nanoparticles. The combination of polymer-zeolite nanocomposite has the potential to come out with the advantages of polymers and zeolites while coping with the deficiencies of both materials. In this study, the synthesis and properties of low-density polyethylene (LDPE) composites with nanozeolite + Y2O3 are investigated. Polyethylene nanocomposite fibers containing nanozeolite + Y2O3 at 5% by mass using a melt extrusion method were composed in a laboratory type twin screw extruder. The thermal properties of the composite fibers were determined by analysis of both thermal gravimetric and differential thermal spectra. Their structural properties were enlightened by scanning electron microscopy, Fourier transform infrared, and ultraviolet absorption. According to the results of X-ray diffraction tests, the samples contain crystals in semicrystalline and alpha form. The mechanical properties of LDPE matrices increased with the addition of nanoparticles. In addition, radioluminescence properties of the polymer were also improved after composing with nanozeolite and Y2O3.Item Detailed luminescence (RL, PL, CL, TL) behaviors of Tb 3+and Dy 3+doped LiMgPO4 synthesized by sol-gel methodKeskin, IÇ; Türemis, M; Kati, MI; Gültekin, S; Arslanlar, YT; Çetin, A; Kibar, RItem Luminescence behaviour of beryl (aquamarine variety) from TurkeyKati, MI; Türemis, M; Keskin, IC; Tastekin, B; Kibar, R; Çetin, A; Can, NNatural blue-green beryl from Turkey has been investigated using scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD) and Cathodoluminescence (CL). Beryl has the chemical formula Be3Al2Si6O18 and is hexagonal with space group P6/mcc. Chemical analyses of the beryl sample utilised inductively coupled plasma-atomic emission spectroscopy (ICP-AES) for major oxides and trace elements. It shows that the beryl sample is rich in Cs (531 ppm) and contains low concentrations of transition-metal ions, in total 2.29 wt.% Fe, 269 ppm Mn, V < 5 ppm and Cr 20 ppm. Ideas on the origin of the green colour of this mineral are presented. The CL spectrum of the bulk sample display intense broad band emission from similar to 360 to similar to 800 nm. (C) 2012 Elsevier B.V. All rights reserved.Item Determination of thermoluminescence kinetic parameters of white and blue chalcedony exposed to X-ray irradiationKeskin, IÇ; Kati, MI; Türemis, M; Çetin, A; Arslanlar, YT; Kibar, RThe study reveals the thermoluminescence (TL) properties of white and blue chalcedony minerals which this mineral mined two different regions (Edirne and Eskisehir, respectively) of Turkey. With the help of various characterization techniques (such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR)), the gem-quality of the samples was tested. The TL glow curves of the samples irradiated with X-rays show intense main TL glow peak having the maximum temperatures at 100 degrees C and 121 degrees C with a heating rate of 2 degrees C/s, respectively. The TL kinetic parameters of the samples are reported here for the first time. Activation energy (E), frequency factor (s) and the order of kinetics (b) of these peaks have been determined in detail by using various heating rates (VHR) and peak shape (PS) methods and verified by Computerized Glow Curve Deconvolution (CGCD). The CGCD method was used to determine the number of peaks associated with the n, glow curves. The values of E calculated with these three methods are a good agreement.Item Structural and tunable optical properties of LiMgPO4:Tb3+ phosphor fabricated by sol-gel methodKati, MIIn the study, Tb3+-doped LiMgPO4 phosphors between .10 and 5 mol% were successfully synthesized by the sol-gel process. The crystal structure of Tb3+-doped LiMgPO4 was identified by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses. The XRD results for LiMgPO4 ceramics doped with Tb3+ indicated a single-phase up to 5 mol%, accompanied by lattice shrinkage. An SEM analysis of LiMgPO4 samples showed that increasing Tb3+ concentration reduced grain size but did not cause any significant change in slightly angular and round grains. The emission intensity of phosphor increased from .10 to 5 mol%, and no concentration quenching was observed. The luminescence color of LiMgPO4:Tb3+ phosphor can be tuned from blue to green through cross-relaxation with the increase in Tb3+ concentration. The photoluminescence emissions of LiMgPO4:Tb3+ on the CIE diagram shifted from blue to green as the Tb3+ concentration increased. The color purity of the 5 mol% Tb3+-doped phosphor showing the strongest emission was measured at 22.71%, whereas the color-correlated temperature parameter was found to be 5573 K. The phosphors exhibited bi-exponential decay profiles, and the observed lifetimes of D-5(3) decreased with the increase of Tb3+, where the cross-relaxation effect increased. The quantum efficiency (eta(QE)) of the phosphor was determined using the cross-relaxation process. For Tb3+ concentrations ranging from .1 to 5 mol%, the eta(QE) of the D-5(3) state decreased from 62.49% to 28.29%. The research may offer a new perspective and new approaches for tuning luminescence in Tb3+-doped phosphors.Item Kinetic parameters and luminescence properties of rare earth (Tb, Nd) doped and transition metal (Mn) doped/co-doped YAlO3 prepared via sol-gel methodGökce, S; Keskin, I; Kati, MI; Kibar, R; Çetin, A; Arslanlar, YTIn this work, phosphor materials with the formula YAlO3 were synthesized via sol-gel method by using the stoichiometric amounts of yttrium nitrate and aluminum nitrate as base materials. The obtained phosphors were doped/co-doped with Tb3+, Nd3+ rare earth ions and Mn2+ transition metal ion. For evaluating the influence of the dopants, the grain size and morphology of the samples by scanning electron microscopy (SEM) and the phase and crystallinity of the synthesized materials by X-ray diffraction (XRD) were investigated. Optical absorption spectra, photoluminescence (PL) and thermoluminescence (TL) were performed to determine a relationship the changing dopant on luminescence properties of YAlO3. Moreover, the kinetic parameters namely activation energy (E), order of kinetics (b) and frequency factor (s) of the synthesized pure and doped materials were calculated using Computerized Glow Curve Deconvolution (CGCD) and Peak Shape Method for a better understanding of the optical properties that change with the doping process. Strong green emission was detected in the sample doped with Mn2+ correspond to 4T1(G)-> 6A1(S) transition. As for YAlO3: Nd3+, characteristic emissions originated from 4G11/2 -> 4I9/2 (-423 nm), 4G9/2 -> 4I9/2 (-460 nm) and 4G7/2 -> 4I9/2 (-540 nm) transitions were seen. The optical band gap of undoped sample was calculated as 2.79 eV and depending on the presence of Nd3+ and Tb3+ dopant ions this value was decreased to the range 2.46-2.56 eV.Item The effect of metal type and gamma irradiation doses on the VOC detection performance of new 1,3-bis(2-pyridylamino)isoindoline complexesGümrükçü, S; Urfa, Y; Altindal, A; Kati, MI; Akyürekli, S; Gül, A; Sahin, Y; Özçesmeci, IIn this study, naphthoxy group substituted 1,3-bis(2-pyridylimino)isoindoline compounds containing nickel and copper metals were synthesized and characterized by NMR, FTIR, UV-vis, and mass spectroscopic methods. Thin film of these compounds is deposited on Plexiglas substrates decorated with Au interdigital electrode structure using spin coating method. The deposited films are then exposed to six doses of gamma irradiation between 1 kGy and 150 kGy using 60 Co as gamma source. The morphological and volatile organic compound (VOC) sensing properties of as-deposited and gamma-irradiated thin films are investigated using Atomic Force Microscopy (AFM) technique and current-time (I-t) measurement set up, respectively. The results of VOC sensing performance have shown that in naphthoxy group substituted 1,3-bis(2-pyridylimino)isoindoline compounds containing nickel and copper metals strongly dependence on the central metal. Under the same conditions, the maximum sensitivity was observed against methanol vapor in the NiBPI-based sensor, while the maximum sensitivity was observed towards ammonia vapor in the CuBPI-based sensor. The results obtained from examining the effect of gamma radiation dose on the VOC sensing performance of the sensors showed that gamma radiation dose has non-negligible effect on the VOC sensing properties of these compounds. For example, the response of CuBPI-based sensor towards ammonia vapors treated by 15 kGy gamma radiation was 18 times higher than that of bare CuBPI based sensor, the results obtained was correlated with the surface roughness of the films.Item Study on structural, morphological, and spectral properties of LiMPO4: Eu3+, B3+(M = Zn, Sr) phosphors and latent fingerprint applicationsIlhan, M; Güleryüz, LF; Kati, MIBoron influences the melting point, crystallization, and both the optical and structural characteristics of ceramic materials. The effect of boron on the structural, morphological, and spectral properties for LiMPO4:xEu3+, yB3+ (where M = Zn or Sr and x = 3 mol%, y = 0-100 mol%) phosphors was investigated using materials fabricated with the solid-state method. In XRD results, LiZnPO4:Eu3+, B3+ series showed a single-phase structure up to 100 mol%, while LiSrPO4:Eu3+, B3+ samples exhibited a low monoclinic phase at low concentrations. In SEM micrographs, the flux effect of boron caused growth in LiMPO4:Eu3+, B3+ (M = Zn, Sr) grains sizes. As the B3+ concentration increases, PL emissions for both phosphor series increased up to 100 mol%, and the luminescence intensities increased over 8 times. Judd-Ofelt (JO) parameters (Q2, Q4) showed a slightly increasing trend for LiZnPO4:Eu3+, B3+, whilst the change in Q2 and Q4 parameters was limited for LiSrPO4:Eu3+, B3+ series. As the B3+ concentration increased, the observed lifetime (z) of LiZnPO4:Eu3+, B3+ with a bi-exponential decay decreased, whereas the z lifetime for LiSrPO4:Eu3+, B3+ with a mono exponential decay increased. The quantum efficiencies for LiSrPO4:Eu3+, B3+ phosphors varied between 89.83 %-96.78 % and exhibited approximately twice the efficiency of LiZnPO4:Eu3+, B3+. The usability of optimized LiMPO4:xEu3+, yB3+ (where M = Zn, Sr and x = 3 mol%, y = 100 mol%) phosphors was investigated for latent fingerprint applications.Item A comparison of spectroscopic properties of Dy3+-doped tetragonal tungsten bronze MTa2O6 (M = Sr, Ba, Pb) phosphors based on Judd-Ofelt parametersIlhan, M; Keskin, IÇ; Güleryüz, LF; Kati, MITTB (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.Item 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 parametersIlhan, M; Kati, MI; Keskin, IÇ; Güleryüz, LFThe 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.Item Gamma irradiated Cu-doped TiO2 nanoparticles for selective ammonia sensingUrfa, Y; Akyuerekli, S; Kati, MI; Corumlu, V; Altindal, AIn this research, the effect of gamma ray doses on volatile organic compound (VOC) sensing properties of Cu doped TiO 2 nanoparticles are studied to further improve the VOC sensing performance. Pure and Cu doped TiO 2 nanoparticles have been prepared by sol -gel technique on Au interdigitated plexiglas substrate and irradiated by gamma-rays with doses varying from 1 to 150 KGy. The irradiation was performed by using 60 Co as gamma source. The structural, morphology and modifications were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), and Atomic Force Microscopy (AFM) techniques. The sensing performance of these films toward ethanol, methanol, 2 -propanol, benzene, toluene, xylene and ammonia vapors has been tested. It was observed that no remarkable sensor response to any vapors except ammonia was observed at room temperature. Changes in sensor ' ammonia sensitivity have been correlated with the gamma radiation dose and Cu doping ratio. Maximum sensing performance was observed with 3% Cu doped TiO 2 exposed to gamma radiation dose of 150 kGy.Item Exploring the effect of boron on the grain morphology change and spectral properties of Eu3+ activated barium tantalate phosphorIlhan, M; Guleryuz, LF; Kati, MIThe effect of the grain morphology on the photoluminescence, charge transfer band, and decay properties was investigated by xEu(3+), yB(3+) (x = 10 mol%, y = 0, 5, 15, 30, 50, 70, and 100 mol%) co-doped BaTa2O6 ceramics fabricated by solid-state reaction. X-ray diffractions of the samples showed that the single-phase structure persisted up to 100 mol% and there was an improvement in crystallinity with increasing B3+ concentration. SEM micrographs of the Eu3+, B3+ co-doped grains showed that the flux effect of boron promotes grain growth and elongated grain shape. The PL emissions of the BaTa2O6:xEu(3+), yB(3+) co-doped phosphors increased up to 100 mol% B3+ concentration, and there was an increase in the intensities of the CTB energy D-5(0 )-> F- 7(1) transition. The increase in PL may be attributed to the increased grain size leading to a decrease in the surface area (SA)/volume (vol) ratio with increasing B3+ concentration, as well as the improvement in crystallinity. However, the decrease in asymmetry ratio was related to the occupation of centrosymmetric (B) sites and the transformation from a rounded/irregular-like to an elongated/rod-like grain shape which has an increasing effect on the SA/vol ratio. The decreasing trend of the Judd-Ofelt parameters (omega(2), and omega(4)) with the increase in boron was related to a high local symmetry of Eu3+ sites, and an increase in the electron density of the surrounding ligands, respectively. The increase in boron led to longer decays in the observed lifetime with bi-exponential characteristics. The CIE diagram and UV lamp photographs of the phosphors showed a color transition from red to orange associated with the increasing magnetic dipole transition. This study may provide an alternative perspective and new strategies to describe the control of grain morphology and luminescence concerning RE-doped phosphors.