MCBÜ Açıkerişim Sistemi :: Browsing by Author "Keskin İ.Ç."

Browsing by Author "Keskin İ.Ç."

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The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dot
(Elsevier B.V., 2017) Keskin İ.Ç.; Türemiş M.; Katı M.İ.; Kibar R.; Şirin K.; Çipiloğlu M.A.; Kuş M.; Büyükçelebi 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. © 2017 Elsevier B.V.
NIR photoluminescence and radioluminescence characteristics of Nd3+ doped BaTa2O6 phosphor
(Blackwell Publishing Ltd, 2018) İlhan M.; Keskin İ.Ç.; 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 4F3/2 → 4I11/2, 4F3/2 → 4I11/2, and 4F3/2 → 4I11/2 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. © 2018 The American Ceramic Society
Determination of thermoluminescence kinetic parameters of white and blue chalcedony exposed to X-ray irradiation
(Elsevier Ltd, 2018) Keskin İ.Ç.; Katı M.İ.; Türemiş M.; Çetin A.; Arslanlar Y.T.; Kibar R.
The study reveals the thermoluminescence (TL) properties of white and blue chalcedony minerals which this mineral mined two different regions (Edirne and Eskişehir, respectively) of Turkey. With the help of various characterization techniques (such as X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR)), 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 °C and 121 °C with a heating rate of 2 °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 TL glow curves. The values of E calculated with these three methods are a good agreement. © 2018 Elsevier Ltd
Structural and optical properties of SrAl2O4: Eu2+/Dy3+ phosphors synthesized by flame spray pyrolysis technique
(Elsevier B.V., 2019) Gültekin S.; Yıldırım S.; Yılmaz O.; Keskin İ.Ç.; Katı M.İ.; Çelik E.
In this study Sr0.985Al2O4:0.005Eu2+/0.01Dy3+ 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 oC. 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 Sr0.985Al2O4:0.005Eu2+/0.01Dy3+ 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 oC under the main glow curve in the sample irradiated by X-ray and He-Ne laser (λexc = 632 nm). RL spectrum of Sr0.985Al2O4:0.005Eu2+/0.01Dy3+ 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. © 2018 Elsevier B.V.
Effects of CdS quantum dot in polymer nanocomposites: In terms of luminescence, optic, and thermal results
(Elsevier Ltd, 2019) Keskin İ.Ç.; Türemiş M.; Kati M.İ.; 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 nanoparticles cause nanocomposites to have lower melting temperatures. © 2018 Elsevier Ltd
Structural, optical, luminescence properties and energy transfer mechanism of Tb3+/Eu3+co-doped SrLa2(MoO4)4 phosphors produced by sol-gel process
(Elsevier Ltd, 2019) Keskin İ.Ç.; Gültekin S.; Katı M.İ.; Türemiş 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 Tb3+and Eu3+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+/Eu3+ 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 Eu3+ (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 Eu3+ 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:Eu3+,Tb3+ phosphors may be potential candidates for light-emitting diode. © 2019 Elsevier B.V.
Evaluation of structural behaviour, radioluminescence, Judd-Ofelt analysis and thermoluminescence kinetic parameters of Eu3+ doped TTB–type lead metaniobate phosphor
(Elsevier B.V., 2020) İlhan M.; Keskin İ.Ç.
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 °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 (Ω2, Ω4), radiative transition rates (Ar) and radiative lifetimes (τr). TL glow curves were monitored by the peaks of 98 and 250 °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 °C) depending on the dose increase were calculated by the PS method. © 2020
Detailed luminescence (RL, PL, CL, TL) behaviors of Tb3+ and Dy3+ doped LiMgPO4 synthesized by sol-gel method
(Elsevier B.V., 2020) Keskin İ.Ç.; Türemiş M.; Katı M.İ.; Gültekin S.; Tuncer Arslanlar Y.; Çetin A.; Kibar R.
The un-doped, Tb3+ and, Dy3+ doped LiMgPO4 phosphors were successfully synthesized by the sol-gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the light-emitting phosphors. The XRD spectra verify the phase formation of samples. The luminescence properties were analyzed by radioluminescence (RL), photoluminescence (PL), cathodoluminescence (CL) and, thermoluminescence (TL) spectra. Also, the effect of Tb3+, Dy3+ ions in LiMgPO4 was determined on the luminescence intensity in detail. The RL spectrum of un-doped LiMgPO4 consists of two broad emission bands in the 310–450 nm and 575–850 nm range. The maximum intensities of these bands were observed at 360 nm and 655 nm. The emission spectrum of Dy3+ doped LiMgPO4 under X-ray excitation show characteristic emissions of Dy3+ corresponds to 4F9/2→6Hj transitions. In addition to the 5D4→7Fj (j:6–1) transitions of Tb3+ doped LiMgPO4 phosphor, strong emissions derived from 5D3→7Fj (j:6–3) transitions were observed in the blue region. Also, these blue emissions were seen at RL, PL and, CL spectra. The optical absorption spectra were recorded and the energy band gaps were calculated 3.62 eV, 3.30 eV and, 4,01 eV for un-doped, Dy3+ and, Tb3+ doped LiMgPO4 phosphors, respectively. The phosphors irradiated with UV (254 nm) light. The main TL glow peak was observed at 288 °C for the Dy3+ doped phosphor, and the peaks at 198, 283 °C were observed for the Tb3+ doped phosphor. © 2020 Elsevier B.V.
Analysis of Judd-Ofelt parameters and radioluminescence results of SrNb2O6:Dy3+phosphors synthesizedviamolten salt method
(Royal Society of Chemistry, 2020) İlhan M.; Keskin İ.Ç.
In this work, Dy3+-doped SrNb2O6phosphors 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:Dy3+exhibited a strong blue emission peak at 576.0 nm related to4F9/2→6H15/2transition of Dy. The high RL emission of the4F9/2→6H15/2(electric dipole) transition upon X-ray-induced excitation led to a decrease in Dy3+local environmental symmetry. The Judd-Ofelt (J-O) theory was applied to the PL excitation spectra for the calculation of optical data such asΩ2,Ω4, andΩ6parameters, radiative transition probability (Ar), branching ratios (β,βexp) and stimulated emission cross-section (σe). The quantum efficiencies (ηQE) 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 Owner Societies 2020.
Assessing of Photoluminescence and Thermoluminescence Properties of Dy3+ Doped White Light Emitter TTB-Lead Metatantalate Phosphor
(Springer, 2020) İlhan M.; Keskin İ.Ç.; 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 μm. The energy transfer efficiency (ηET) energy transfer rate (W) and quantum efficiency (ηQE) of the whole process were found as 56.25%, 1.581 ms–1, and 20.27%, respectively. The CIE (Commission Internationale de l’Éclairage) 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°C and 400°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. © 2020, The Minerals, Metals & Materials Society.
Characterization and determination of thermal and radioluminescence properties of low-density polyethylene (LDPE)-(nanozeolite + Y2O3) composite
(SAGE Publications Ltd, 2020) Çanlı M.; Keskin İ.Ç.; Türemiş M.; Sirin K.; Katı M.İ.
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 α 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. © The Author(s) 2019.
Comprehensive study on structural, thermal, morphological and luminescence (RL, PL, TL) properties of CaLa2(WO4)4: Tb3+, Dy3+ phosphors synthesized via sol-gel method
(Elsevier Ltd, 2021) Türemiş M.; Keskin İ.Ç.; Katı M.İ.; 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+, Dy3+phosphors may be one of the potential candidates for light-emitting diode. © 2021 Elsevier Ltd and Techna Group S.r.l.
The role of Eu3+ ion on luminescence, TL kinetic parameters and electrochemical behaviors of Sr0,5Ca0,5WO4 phosphor synthesized via sol-gel technique; [Sol-jel tekniği ile sentezlenmiş Sr0,5Ca0,5WO4 fosforunda Eu3+ iyonunun lüminesans, TL kinetik parametreler ve elektrokimyasal davranışındaki rolü]
(TUBITAK, 2021) Kati M.İ.; Keskin İ.Ç.; Türemiş M.; Çetin A.; Kibar R.
The Eu3+doped Sr0,5Ca0,5WO4 has been synthesized by the sol-gel method for the first time. The phosphors were analyzed by XRD, SEM, DTA/TG optical absorption spectra, radioluminescence (RL), photoluminescence (PL), and thermoluminescence (TL) spectra. The energy transfer mechanism was determined on Eu3+ doped Sr0,5Ca0,5WO4 phosphor. The XRD results reveal that the samples exhibit a tetragonal scheelite structure. FT-IR spectra provide the proof of scheelite structure with W-O anti-symmetric stretching vibration in [WO4]2- tetrahedrons at 750-910 cm-1. The Sr0,5Ca0,5WO4 phosphor showed a broad emission between 350-750 nm with a maximum of 506 nm. Sr0,5Ca0,5WO4:0.5Eu3+ phosphor exhibit characteristic emissions of Eu+3 (545, 592, 614, 650, and 700 nm) in the RL spectrum. The host material has excellent energy transfer efficiency for lanthanide ions. The kinetic parameters were calculated by the computerized glow curve deconvolution (CGCD) analysis method. As a result of CGCD, three peaks (Etrap:0.74-1.46 eV) for un-doped Sr0,5Ca0,5WO4 and five peaks (Etrap:0.75-1.28 eV) for Sr0,5Ca0,5WO4: Eu3+ were determined under main TL glow curve. In the cyclic voltammogram of the doped sample, an oxidation peak of about-0.4 eV, which is thought to be derived from Eu3+, was observed. Based on the results, the Sr0,5Ca0,5WO4:Eu+3 phosphors may be potential applicants for LEDs. © 2021, TUBITAK. All rights reserved.
Judd-Ofelt parameters and X-ray irradiation results of MNb2O6:Eu3+(M = Sr, Cd, Ni) phosphors synthesizedviaa molten salt method
(Royal Society of Chemistry, 2021) İlhan M.; Ekmekçi M.K.; Keskin İ.Ç.
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 with5F0→7Fjtransitions, and strong peaks occurred at the5D0→7F2transition. 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 (Ω2,Ω4) from the PL emission spectrum. The quantum efficiencies (ηQE%) of MNb2O6:Eu3+(M = Sr, Cd, Ni) phosphors with the highest emission were found as 61.87%, 41.89%, and 11.87% respectively. Bandwidths (σe× Δλeff) and optical gains (σe×τ) of MNb2O6:Eu3+(M = Sr, Cd, Ni) phosphors with highest emissions were found as follows; 24.182 × 10−28, 28.674 × 10−28, 38.647 × 10−28cm3and 20.441 × 10−25, 13.790 × 10−25, 3.987 × 10−25cm2s, respectively, corresponding to the5D0→7F2transition. © The Royal Society of Chemistry 2021.
A comparison of spectroscopic properties of Dy3+-doped tetragonal tungsten bronze MTa2O6 (M = Sr, Ba, Pb) phosphors based on Judd–Ofelt parameters
(Springer, 2022) İlhan M.; Keskin İ.Ç.; Güleryüz L.F.; Katı M.İ.
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 (Ω2, Ω4, Ω6). The decreasing trend of Ω2 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 Ω2 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. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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 Ltd, 2022) İlhan M.; Katı M.İ.; Keskin İ.Ç.; Güleryüz L.F.
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 Ω2 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 (βexp) and Judd-Ofelt (βcal) branching ratios for transition 5D0→7F2 are well below 10%, indicating good consistency. All the 5D0 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. © 2022 Elsevier B.V.
Kinetic parameters and luminescence properties of rare earth (Tb, Nd) doped and transition metal (Mn) doped/co-doped YAlO3 prepared via sol-gel method
(Elsevier B.V., 2023) Gökçe S.; Keskin İ.Ç.; Katı M.İ.; Kibar R.; Çetin A.; Tuncer Arslanlar Y.
In 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. © 2023 Elsevier B.V.
Thermoluminescence Kinetic Parameters and Radioluminescence of RE3+ (RE = Pr, Sm, Tb, Ho, Er)-Doped Barium Tantalate Phosphors
(Springer, 2023) Keskin İ.Ç.; İlhan 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 3P0 → 3H4 and 1D2 → 3H4, while the RL emissions of Tb3+ were observed corresponding to transitions of5D4 → 7FJ. 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 °C and 400 °C at a heating rate of 2 °C s−1. TL glow peaks for Pr3+, Tb3+, and Er3+ formed at temperatures of 77 °C and 208 °C, 87 °C and 263 °C, and 158 °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. © 2023, The Minerals, Metals & Materials Society.
Evaluation of the Structural, Near-Infrared Luminescence, and Radioluminescence Properties of Nd3+ Activated TTB-Lead Metatantalate Phosphors
(Turkish Chemical Society, 2023) İlhan M.; Keskin İ.Ç.
The study reports the structural and spectroscopic properties of Nd3+ doped lead metatantalate phosphor series fabricated by conventional solid state method. XRD results of the PbTa2O6 phase confirm the tungsten bronze symmetry and single-phase structure between 0.5 and 10 mol% Nd3+ concentrations. The lead decrease in the structure can be associated with maintaining the charge balance and single phase due to evaporation during sintering. In SEM micrographs, the grains exhibited shapeless morphology, and the grain sizes varied from 0.5 to 7 m. In EDS results, the increase of Ta/Pb ratio in grain surfaces indicated some lead evaporation, as reported in previous studies. The absorption spectrum of PbTa2O6 host peaked around 275-280 nm, and the band gap was found to be 3.7±0.2 eV. The absorptions of Nd3+ doped phophors shifted the high wavelenght or the low band gap, where the band gaps were found between 3.1±0.2 and 3.3±0.2 eV. The PL emissions of the phosphors in near-inrared region were observed with the transitions of 4 F3/2→4I9/2 (at 875 nm) and4F3/2→4I11/2 (at 1060 nm) of Nd3+. The RL emissions or X-ray excited luminescence were monitored with the transitions of4F3/2→4I9/2 (at 875 nm),4F3/2→4I11/2 (at 1065 nm) in the infrared region, and the transitions of2F(2)5/2→4F9/2,2F(2)5/2→2H(2)11/2,2F(2)5/2→4G5/2,2F(2)5/2→4G7/2,2F(2)5/2→4G9/2 in the visible region corresponding to at around 430, 455, 490, 525, and 570 nm, respectively. PL and RL emissions of the phosphors exhibited the decreasing emission intensity over 5 mol% due to the concentration quenching which may be associated with cross-relaxing mechanism. In the PL and RL spectral profiles, the similarity of splitting levels was attributed to the similarity of the local symmetry of the ligand ions surrounding the Nd3+ ion. The CIE coordinates obtained using RL emissions were found close to the blue region due to visible region transitions. © 2023, Turkish Chemical Society. All rights reserved.
Luminescence characteristics and kinetic parameters of LiBaPO4: Tb3+, Dy3+ phosphors synthesized by sol-gel method
(Elsevier B.V., 2024) Katı M.İ.; Gökçe S.; Keskin İ.Ç.; Türemiş 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 °C, 145 °C and 204 °C, while the main temperature peak is measured at 240 °C for Tb3+ doped sample. Chromotographic studies of LiBa0·98PO4: Dy3+0.02 reveals that calculated x and y color coordinates (0.3122, 0.3233) are very close to the white light. © 2023

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