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Browsing by Author "Ilhan, M"

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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).
Influence of Boron Doping on the Dielectric Characteristics of Eu3+-Doped β-SrTa2O6 and Eu3+-Doped BaTa2O6 Tungsten Bronze-Type Ceramics
Ilhan, M; Kati, MI; Sahin, N; Esmer, K
The 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.
Microstructural and Radioluminescence Characteristics of Nd3+ Doped Columbite-Type SrNb2O6 Phosphor
Ekmekçi, MK; Ilhan, M; Ege, A; Ayvacikli, M
Undoped and different concentration Nd3+ doped SrNb2O6 powders with columbite structure were synthesized by molten salt process using a mixture of strontium nitrate and niobium (V) oxide and NaCl-KCl salt mixture as a flux under relatively low calcining temperature. X-ray diffraction analysis results indicated that SrNb2O6 phases found to be orthorhombic columbite single phase for undoped, 0.5 and 3 mol% Nd3+ doping concentrations. Phase composition of the powders was examined by SEM-EDS analyses. Radioluminescence properties of Nd3+ doped samples from UV to near-IR spectral region were studied. The emissions increased with the doping concentration of up to 3 mol%, and then decreased due to concentration quenching effect. There is a sharp emission peak around 880 nm associated with F-4(5/2) -> I-4(9/2) transition in the Nd3+ ion between 300 and 1100 nm. The broad emission band intensity was observed from 400 to 650 nm where the peak intensities increased by increasing Nd3+ doping concentration. All the measurements were taken under the room temperature.
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.
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.
Effect of boron incorporation on the structural, morphological, and spectral properties of CdNb2O6:Dy3+phosphor synthesized by molten salt process
Ilhan, M; Ekmekçi, MK; Güleryüz, LF
The effect of boron addition on the structural, morphologic and spectral properties was investigated by using xDy3+ (x = 0.5, 3, 6 mol%) doped, and xDy3+, yB3+ (y = 0, 5, 15, 25 mol%) co-doped CdNb2O6 powders produced by molten salt method. X-ray diffractions (XRD) of all Dy3+ doped, and B3+, Dy3+ co-doped samples showed that they retained the single-phase structure. The homogeneous dissolution of the Dy3+ doping without forming an impurity phase in the structure can be attributed to the flux effect of the molten salt process and boron doping. Scanning electron microscopy (SEM) micrographs of the B3+, Dy3+ co-doped grains showed that the effect of boron promotes grain growth and prismatic-like grain shape. Photoluminescence (PL) emissions of the phosphors with the excitation of 351.9 nm were monitored by the 4F9/2 -> 6H15/2, 4F9/2 -> 6H13/2, and 4F9/ 2 -> 6H11/2 transitions. PL excitations and a broad peak at 275 nm originating from the O2--> Nb5+ band transition were observed with the emission of 577.9 nm. The PL emissions of Dy3+, B3+ co-doped phosphors increased about two fold compared to Dy3+ doped samples. The increase in PL may be related to the increased presence of luminescence centers at or near grain surface due to the decreasing surface area (SA)/volume (V) ratio as the growth of B3+ co-doped grains and the transformation from rod-like to prismatic-like shape. The increased Dy3+ presence led to a decrease in observed lifetime, while the B3+ increase did not cause any change. The study may provide a different perspective for the understanding and controlling of grain morphology and the luminescence relation for RE-doped phosphors.
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.
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.
Investigation of radial turbines for wind energy harvesting
Gürbüz, MT; Ilhan, M; Acarer, S; Karadeniz, ZH
Wind energy has been a research focus of the last few decades, promoting the topic to a much more matured level. However, the body of literature is built around a limited number of turbine types and it is still beneficial to increase turbine diversity for the opportunity to select optimal turbine for a given purpose. The radial (inflow) turbines known in gas and hydro turbine industries for pressurized pipe flows are undiscovered turbines for free-stream wind harvesting both in air and underwater. In such case, the wind tangentially interacts with each blade by an external casing; therefore, all blade angular positions may, at least in theory, contribute equally to power production. Enclosed compact architecture with low rotational speeds and narrow intake ports may possess advantages in enabling the use of much weaker but more recyclable and long-lasting blades and in applications such as integrated wind harvesting for blunt bodies like buildings, vessels and devices or for any application where an open rotor is not feasible. Using experimentally validated Reynolds-averaged Navier-Stokes simulations, mass swallowing capacities and corresponding efficiencies of such turbines are parametrically investigated at low Reynolds numbers, Re-chord=11 x 10(3), and finally enhancement is shown in 88 x 10(3). Findings provide first insights into such turbines. Considering the investigated very low Reynolds numbers and three-dimensional effects, comparable performance with other small turbines are observed. Moreover, undiscovered potential for performance optimization persists.
Study on structural, morphological, and spectral properties of LiMPO4: Eu3+, B3+(M = Zn, Sr) phosphors and latent fingerprint applications
Ilhan, M; Güleryüz, LF; Kati, MI
Boron 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.
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.
Exploring the effect of boron on the grain morphology change and spectral properties of Eu3+ activated barium tantalate phosphor
Ilhan, M; Guleryuz, LF; Kati, MI
The 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.

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