MCBÜ Açıkerişim Sistemi :: Browsing by Author "Türemis, M"

Browsing by Author "Türemis, M"

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Effects of CdS quantum dot in polymer nanocomposites: In terms of luminescence, optic, and thermal results
Keskin, IÇ; Türemis, M; Kati, MI; Kibar, R; Çetin, A
CdS 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.
Luminescence characteristics and kinetic parameters of LiBaPO4: Tb3+, Dy3+phosphors synthesized by sol-gel method
Kati, MI; Gökce, S; Keskin, IÇ; Türemis, M; Çetin, A; Kibar, R
LiBaPO4: 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.
Comprehensive study on structural, thermal, morphological and luminescence (RL, PL, TL) properties of CaLa2(WO4)4: Tb3+, Dy3+ phosphors synthesized via sol-gel method
Türemis, M; Keskin, IÇ; Kati, MI; Çetin, A; Ay, K; Kibar, R
Tb3+/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.
The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dot
Keskin, IÇ; Türemis, M; Kati, MI; Kibar, R; Sirin, K; Çipiloglu, MA; Kus, M; Büyükcelebi, S; Çetin, A
In 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.
X-ray irradiated thermo- and radioluminescence, structural and thermal characterization of septarian (powder&bulk) from Madagascar
Keskin, IÇ; Kati, MI; Türemis, M; Gültekin, S; Üstün, S; Çetin, A; Kibar, R
The 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.
Optimizing Optical and Structural Properties of Nanocomposites by ZnO and BP-3
Türemis, M; Keskin, IÇ; Kati, MI; Kibar, R; Sirin, K; Çanli, M; Çorumlu, V; Çetin, A
This 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.
Characterization and determination of thermal and radioluminescence properties of low-density polyethylene (LDPE)-(nanozeolite + Y2O3) composite
Çanli, M; Keskin, IÇ; Türemis, M; Sirin, K; Kati, MI
Nanotechnology 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.
Detailed luminescence (RL, PL, CL, TL) behaviors of Tb 3+and Dy 3+doped LiMgPO4 synthesized by sol-gel method
Keskin, IÇ; Türemis, M; Kati, MI; Gültekin, S; Arslanlar, YT; Çetin, A; Kibar, R
Luminescence behaviour of beryl (aquamarine variety) from Turkey
Kati, MI; Türemis, M; Keskin, IC; Tastekin, B; Kibar, R; Çetin, A; Can, N
Natural 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.
Determination of thermoluminescence kinetic parameters of white and blue chalcedony exposed to X-ray irradiation
Keskin, IÇ; Kati, MI; Türemis, M; Çetin, A; Arslanlar, YT; Kibar, R
The 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.
Structural, optical, luminescence properties and energy transfer mechanism of Tb3+/Eu3+co-doped SrLa2(MoO4)4 phosphors produced by sol-gel process
Keskin, IÇ; Gültekin, S; Kati, MI; Türemis, M; Ay, K; Arslanlar, Y; Çetin, A; Kibar, R
Tb3+/Eu3+ co-doped SrLa2(MoO4)(4) have been synthesized using the sol-gel process. The as-produced light-emitting phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA)/thermogravimetric analysis (TG), optical absorption spectra, radioluminescence (RL), and photoluminescence (PL) spectra. The effect of Tb(3+)and Eu(3+)doping concentrations on the RL and PL intensity of host material was analyzed in details. Furthermore, the energy transfer mechanism based on RL spectra were determined of Tb3+/Eu(3+)co-doped SrLa2(MoO4)(4) phosphors. When the samples excited by X-ray, the SrLa2(MoO4)(4) phosphors exhibit characteristic emissions of Tb3+ (489, 544, 586, 620 and 675 nm) and Eu(3+)d (545, 592, 614, 650 and 700 nm). Also, similar emissions are observed in the results of PL spectra, when the samples excited by 488 nm. The host material has excellent energy transfer efficiency for lanthanide ions. In addition, the luminescence spectra indicated that the energy transfer is also effective between from Tb3+ to Eu(3+)and vice versa. The CIE parameters are calculated to characterize the color emission. Under UV excitation, the synthesized materials display different color from green to red. Based on the results, the SrLa2(MoO4)(4:Eu)(3+)(3+)(,Tb) phosphors may be potential candidates for light-emitting diode. (C) 2019 Elsevier B.V. All rights reserved.

Browsing by Author "Türemis, M"

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