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Browsing by Author "Keskin, IÇ"

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Photoluminescence, radioluminescence and thermoluminescence properties of Eu3+ doped cadmium tantalate phosphor
Ilhan, M; Keskin, IÇ
For investigate spectroscopic properties, Eu3+ doped columbite type CdTa2O6 phosphors were synthesized using the solid state reaction method. The synthesized ceramic phosphors were investigated by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), photoluminescence (PL), radioluminescence (RL) and thermoluminescence (TL) analyses. CdTa2O6:Eu3+ phosphors exhibited emissions at 591.8 nm and 612.1 nm because of the characteristic band transitions of the Eu3+ ion. Phosphor emission increased with increasing Eu3+ ion dopant up to 1.5 mol%, and then decreased owing to concentration quenching. The decay times decreased with increasing Eu3+ dopant, while they were varied from 711 to 534 m. The scintillation emissions of Eu3+ doped samples from the UV to near-IR spectral region were monitored by RL measurements. The high RL emission may be attributed to the good scintillation property of phosphor. TL glow curves were monitored for different Eu3+ concentrations in the range of 50 degrees C to 400 degrees C at a heating rate of 2 degrees C s(-1), after being irradiated under short-wave UV light (254 nm).
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.
Analysis of Judd-Ofelt parameters and radioluminescence results of SrNb2O6:Dy3+ phosphors synthesized via molten salt method
Ilhan, M; Keskin, IÇ
In this work, Dy3+-doped SrNb(2)O(6)phosphors were fabricated by the molten salt process, which avoids high sintering temperatures, prolonged reaction time and poor compositional homogeneity. All samples crystallized to the orthorhombic columbite structure with space group,P21/c, while a rod-like morphology was observed by scanning electron microscopy (SEM). PL (photoluminescence) and RL (radioluminescence) spectra of SrNb2O6:Dy(3+)exhibited a strong blue emission peak at 576.0 nm related to(4)F(9/2)->(6)H(15/2)transition of Dy. The high RL emission of the(4)F(9/2)-> H-6(15/2)(electric dipole) transition upon X-ray-induced excitation led to a decrease in Dy(3+)local environmental symmetry. The Judd-Ofelt (J-O) theory was applied to the PL excitation spectra for the calculation of optical data such as omega(2),omega(4), and omega(6)parameters, radiative transition probability (A(r)), branching ratios (beta,beta(exp)) and stimulated emission cross-section (sigma(e)). The quantum efficiencies (eta(QE)) varied between 35.47 and 31.93%, which are compatible with theoretical quantum efficiencies based on the Einstein relation. The CIE chromaticity coordinates (x,y) and CCT (correlated color temperature) parameter for 3 mol% phosphor were defined (0.385, 0.432) and 4209 K, respectively.
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.
Evaluation of structural behaviour, radioluminescence, Judd-Ofelt analysis and thermoluminescence kinetic parameters of Eu3+ doped TTB-type lead metaniobate phosphor
Ilhan, M; Keskin, IÇ
In this study, the structural and spectroscopic properties of orthorhombic PbNb2O6 doped with different concentrations of Eu3+ were studied. Interestingly, XRD analysis of undoped PbNb2O6 showed rhombohedral phase while Eu3+ doped structures exhibited an orthorhombic phase at 1250 degrees C. This difference was also observed in the morphology and composition of grains by SEM-EDS analysis. PL and RL emissions occurred between 550 and 850 nm owing to the 4f-4f transitions of Eu3+ . The Judd-Ofelt theory was applied to the experimental data for determination of the Judd-Ofelt parameters (Omega(2), Omega(4)), radiative transition rates (A(r)) and radiative lifetimes (tau(r)). TL glow curves were monitored by the peaks of 98 and 250 degrees C while emission increased up to 6 mol%. TL emission of 6 mol% phosphor depending on X-ray irradiation dose exhibited the highest intensity for 1200 Gy and appeared new peaks. Moreover, the TL emission of phosphor showed a linear relation with X-ray irradiation. The deconvolution peaks of 1200 Gy irradiated samples were determined by the CGCD method. Kinetic data of first peak (98 degrees C) depending on the dose increase were calculated by the PS method.
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.
Assessing of Photoluminescence and Thermoluminescence Properties of Dy3+ Doped White Light Emitter TTB-Lead Metatantalate Phosphor
Ilhan, M; Keskin, IÇ; Gültekin, S
Trivalent Dy doped TTB (tetragonal tungsten bronze) lead tantalate (PbTa2O6) phosphors were synthesized by the solid-state reaction route. Structural and spectroscopic properties have been carried out by x-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), photoluminescence (PL) and thermoluminescence (TL) analyses. XRD patterns of samples revealed the presence of TTB symmetry which continued up to 10 mol.%. SEM analysis showed the transformation of grain morphology from the shapeless-rounded to elongate. Strong PL emissions of PbTa2O6:Dy3+ phosphor were monitored at 480.5 nm and 578.5 nm. PL emission increased up to 7 mol.% and then decreased because of the concentration quenching. Decay times decreased with the increase of concentration and the end of the process (10 mol.%) fell to 355 mu m. The energy transfer efficiency (eta(ET)) energy transfer rate (W) and quantum efficiency (eta(QE)) of the whole process were found as 56.25%, 1.581 ms(-1), and 20.27%, respectively. The CIE (Commission Internationale de l'eclairage) coordinates of all phosphors have located close to the standard white light center, also the CIE coordinates (x, y) and CCT (correlated color temperature) value for 7 mol.% phosphor were found as (0.310, 0.295) and 6238 K, respectively. TL emissions of PbTa2O6:Dy3+ phosphor were monitored by four glow peaks in the range between 50 degrees C and 400 degrees C after x-ray irradiation. TL kinetic parameters were determined by the deconvolution of the 5 mol.% sample which has the highest glow curve intensity.
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.
Structural and optical properties of SrAl2O4: Eu2+/Dy3+ phosphors synthesized by flame spray pyrolysis technique
Gültekin, S; Yildirim, S; Yilmaz, O; Keskin, IÇ; Kati, MI; Çelik, E
In 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.
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
Thermoluminescence Kinetic Parameters and Radioluminescence of RE3+ (RE = Pr, Sm, Tb, Ho, Er)-Doped Barium Tantalate Phosphors
Keskin, IÇ; Ilhan, M
The thermoluminescence (TL) kinetic parameters and radioluminescence results (RL) of RE3+ (RE = Pr, Sm, Tb, Ho, Er)-doped barium tantalate phosphors have been studied for different concentrations. The concentration quenching occurring at the RL intensity of Pr3+ after 1.5 mol% was associated with a cross-relaxation between P-3(0) -> H-3(4) and D-1(2) -> H-3(4), while the RL emissions of Tb3+ were observed corresponding to transitions of(5)D(4) -> F-7(J). The asymmetry ratio of RL is relatively high compared to the PL asymmetry ratio for Sm3+, which may be attributed to the RL mechanism leading to some decrease in the local symmetry of Sm3+ ions. The Ho3+ and Er3+ show the characteristic green and red emissions corresponding to radiative transitions. Also, the spectral properties of the phosphors have been discussed by comparing the RL results, the reported PL results of Pr3+, Sm3+, Ho3+, Er3+ , and the PL results of Tb3+ , which were examined in the study. After being irradiated by x-ray and short-wave UV light (254 nm), TL glow curves for Pr3+, Tb3+, and Er3+ doped phosphors were compared in the range of 50 degrees C and 400 degrees C at a heating rate of 2 degrees C s(-1). TL glow peaks for Pr3+, Tb3+, and Er3+ formed at temperatures of 77 degrees C and 208 degrees C, 87 degrees C and 263 degrees C, and 158 degrees C and 267 C, respectively. The kinetic data were estimated by applying computerized glow curve deconvolution (CGCD) where TL glow curves of BaTa2O6:RE3+ (RE = Pr, Tb, Er) consist of 5, 6, and 7 estimated glow peaks with figure-of-merit values of 1.06, 1.60, and 1.09, respectively.
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.
A comparison of spectroscopic properties of Dy3+-doped tetragonal tungsten bronze MTa2O6 (M = Sr, Ba, Pb) phosphors based on Judd-Ofelt parameters
Ilhan, M; Keskin, IÇ; Güleryüz, LF; Kati, MI
TTB (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.
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
Ilhan, M; Kati, MI; Keskin, IÇ; Güleryüz, LF
The 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.
Judd-Ofelt parameters and X-ray irradiation results of MNb2O6:Eu3+ (M = Sr, Cd, Ni) phosphors synthesized via a molten salt method
Ilhan, M; Ekmekçi, MK; Keskin, IÇ
Trivalent Eu-activated MNb2O6 (M = Sr, Cd, Ni) ceramic phosphors were produced using the molten salt route, which involves a low sintering temperature and provides improved homogeneity. The photoluminescence (PL) and radioluminescence (RL) spectra of phosphors exhibited characteristic Eu3+ emissions with F-5(0) -> F-7(j) transitions, and strong peaks occurred at the D-5(0) -> F-7(2) transition. The PL and RL emissions of SrNb2O6:Eu3+ decreased over 3 mol%, while both emissions for CdNb2O6:Eu3+ and NiNb2O6:Eu3+ increased with increasing Eu3+ concentration. The spectral properties of phosphors were evaluated by determining Judd-Ofelt intensity parameters (omega(2), omega(4)) from the PL emission spectrum. The quantum efficiencies (eta(QE)%) of MNb2O6:Eu3+ (M = Sr, Cd, Ni) phosphors with the highest emission were found as 61.87%, 41.89%, and 11.87% respectively. Bandwidths (sigma(e) x Delta lambda(eff)) and optical gains (sigma(e) x tau) of MNb2O6:Eu3+ (M = Sr, Cd, Ni) phosphors with highest emissions were found as follows; 24.182 x 10(-28), 28.674 x 10(-28), 38.647 x 10(-28) cm(3) and 20.441 x 10(-25), 13.790 x 10(-25), 3.987 x 10(-25) cm(2) s, respectively, corresponding to the D-5(0) -> F-7(2) transition.
NIR photoluminescence and radioluminescence characteristics of Nd3+ doped BaTa2O6 phosphor
Ilhan, M; Keskin, IÇ; Çatalgöl, Z; Samur, R
Barium tantalate phosphors activated with different concentrations of Nd3+ ion were synthesized via conventional solid state reaction method. The synthesized ceramic powders were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), laser diode (LD) excited near infrared (NIR) photoluminescence and X-ray induced radioluminescence (RL) analyses. In XRD results, Nd3+ doped BaTa2O6 structure with tetragonal tungsten bronze (TTB) symmetry was observed to continue up to 10 mol%. In the examination of ceramic powders by SEM, grain size decreased with the increasing doping concentration. By using laser diode excited NIR photoluminescence of BaTa2O6:Nd3+ phosphor exhibited characteristic emissions at 877, 1080, and 1376 nm wavelengths due to F-4(3/2) I-4(11/2), F-4(3/2) I-4(11/2), and F-4(3/2) I-4(11/2) band transitions respectively. Scintillation properties of Nd3+ doped samples from UV to near-IR spectral region were carried out by the radioluminescence analysis. NIR and scintillation emissions initially increased by the doping concentration, and then decreased due to concentration quenching effect.
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.
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.

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