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Öğe Anomalous heating rate response of beta irradiated Sm3+ and Tb3+ doped BaAl2O4 phosphors(Elsevier Science Sa, 2018) Kaynar, U. H.; Guvener, E.; Ayvacikli, M.; Dogan, T.; Balci-Yegen, S.; Oglakci, M.; Topaksu, M.The stuffed derivative of the tridymite structure, the oxide BaAl2O4 has been regarded as a long persistent phosphor. Thermoluminescence (TL) glow curve peaks of thin pellet samples of undoped and, Sm3+ and Tb3+ doped BaAl2O4 prepared by combustion method was reported. The structure of the compounds was monitored by X-ray diffraction and found a single-phase compound with a hexagonal structure. Performing a series of TL measurements for the temperature range from room temperature to 400 degrees C, the effect of beta radiation dose on TL response, various TL heating rate (HR) properties of undoped and Sm3+ and Tb3+ doped BaAl2O4 phosphors were investigated. Peak shape method was also utilized to assess the trap parameters. The activation energy of the main peak at 128 degrees C was found to be 0.97 eV. TL glow curves obtained from undoped and Tb3+ doped BaAl2O4 decrease with increasing HR value (varying from 0.5 to 15 degrees C s(-1)) in a way matching with thermal quenching effect. Contrary to expectations, anomalous HR dependence was observed on Sm3+ doped BaAl2O4 sample and a semi-localized transition model has been used in order to explain such behaviour. (C) 2018 Elsevier B.V. All rights reserved.Öğe Characterization, room and low temperature photoluminescence of yttrium aluminium borate activated with Sm3+ions(Pergamon-Elsevier Science Ltd, 2023) Madkhli, A. Y.; Kaynar, U. H.; Coban, M. B.; Ayvacikli, M.; Canimoglu, A.; Can, N.In this study, the combustion method assisted by urea that is ideally suited to economic and time saving was used for the synthesizing of reddish orange emitting YAl3(BO3)4 phosphor samples doped with various Sm3+ ions (from 0.01 wt% to 7wt%). A detailed study of the structural and luminescence properties at room/low tem-perature of the synthesized samples was performed. XRD analysis revealed a rhombohedral structure with an R32 space group (155). The particle size was determined by the Scherrer's method to be 48 nm. The visible PL emission spectra upon excitation at 359 nm are recorded and four emission peaks around 564, 599, 646, and 707 nm with transitions 4G5/2 -> 6H5/2, 4G5/2 -> 6H7/2, 4G5/2 -> 6H9/2 and 4G5/2 -> 6H11/2 are observed. Concentration quenching was mainly caused by dipole-dipole interactions between neighbouring trivalent Sm3+ ions. Through the CIE chroma coordinates (0.606, 0.382), the optimized sample (x = 0.03) demonstrates admirable luminous performance. YAl3(BO3)4:Sm3+ can be a good candidate for use as a red component for lighting applications.Öğe Enhancement of luminescence and thermal stability in Eu3+-doped K3Y (BO2)6 with Li+ and Na+ co-doping(Elsevier, 2024) Kaynar, U. H.; Aydin, H.; Altowyan, A. S.; Hakami, J.; Coban, M. B.; Ayvacikli, M.; Karali, E. EkdalEu3+-doped and Li+/Na+ co-doped K3Y(BO2)6 (KYBO) phosphors were synthesized through a microwave- assisted sol-gel method, and their structural and photoluminescent (PL) characteristics were examined. X-ray diffraction (XRD) and Rietveld refinement confirm effective dopant incorporation and preservation of the crystalline structure. Fourier Transform Infrared (FTIR) spectroscopy indicates the maintenance of the borate structure, confirming the structural integrity of the phosphors upon doping. The addition of Li+ and Na+ co-dopants notably enhances luminescent efficiency and thermal stability, making these phosphors promising candidates for solid-state lighting (SSL) applications. PL analysis reveals strong red emission peaks at 612 nm, attributed to the 5 D o ? 7 F 2 transition of Eu3+ ions. The study indicates that electric dipole-quadrupole interactions are the primary mechanism for energy migration, with a critical distance of approximately 22.68 & Aring;. This mechanism contributes to concentration quenching at higher doping levels. High temperature PL measurements indicated an activation energy of 0.1389 eV for thermal quenching in the Li+ co-doped sample. Additionally, the Na+ co-doped sample exhibited an abnormal thermal stability behavior, with an even higher activation energy of 0.2536 eV. This suggests that Na+ co-doping significantly enhances the thermal resilience of the phosphor, making it more suitable for high-power light-emitting applications that operate under extreme conditions. CIE chromaticity diagrams highlight the potential for optimizing Eu3+ doping levels, combined with Li+ and Na+ co-doping, to improve luminescent performance and thermal stability for advanced SSL applications. (c) 2024 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights are reserved, including those for text and data mining, AI training, and similar technologies.Öğe Integrating K plus into Eu and Tb doped GdCa 4O(BO3)3: A dual study on photoluminescence and structure(Elsevier Science Sa, 2024) Altowyan, Abeer S.; Kaynar, U. H.; Hakami, Jabir; Coban, M. B.; Ayvacikli, M.; Aydin, H.; Canimoglu, A.In this study, we investigate the structural and photoluminescence (PL) properties of rare -earth -doped GdCa 4 O (BO 3 ) 3 (GdCOB) phosphors, specifically focusing on the spectral behaviour induced by doping with Eu 3 + and Tb 3 + ions. The powder X-ray diffraction (XRD) spectra confirm the formation of a monoclinic phase. The XRD data were also refined by a Rietveld refinement method. The existence of B, O, Ca, Gd, Tb, Eu and K elements was verified by EDS spectra. We introduce a detailed examination of the charge compensation process using Kro ger- Vink notation to clarify the mechanisms essential for tailoring the optical properties of the phosphors. The PL excitation spectrum of GdCOB:Eu 3 + , monitored at 611 nm, reveals sharp excitation peaks at 319, 361, 380, and 392 nm, corresponding to 7 F 0 -> 5 H 3 , 7 F 0 -> 5 D 4 , 7 F 0 -> 7 F 0 , and 7 F 0 -> 5 L 6 transitions, respectively. The PL spectrum under excitation of 392 nm exhibits that phosphors doped with Eu 3 + a significant red emission at 611 nm, which is attributed to the 5 D 0 -> 7 F 2 transition. This emission intensity is particularly enhanced at non-centrosymmetric sites of the Eu 3 + ions. Similarly, the PL excitation spectrum of GdCOB:Tb 3 + , monitored at 552 nm, displays distinct excitation peaks at 316, 341, 353, and 379 nm, which correspond to the transitions 7 F 6 -> 5 D 0, 7 F 6 -> 5 L 7, 7 F 6 -> 5 D 2, and 7 F 6 -> 5 D 3, respectively. Tb 3 +-doped phosphors display a bright green emission, with a dominant peak at 552 nm, resulting from the 5 D 4 -> 7 F 5 transition. Additionally, the introduction of K + ions as co-dopants results in modifications to the local environments of Eu 3 + and Tb 3 + ions. These changes allow for fine-tuning of the emission peaks, significantly enhancing the luminescent output of the phosphors. Optimal doping concentrations of 5 mol% for Eu 3 + and 1 mol% for Tb 3 + enhance luminescent intensity and prevent concentration quenching. This phenomenon, often resulting in reduced PL intensity at higher dopant levels, is primarily due to dipole -dipole interactions, consistent with Dexter's theory of energy transfer. Strategic modulation of doping concentrations, coupled with a deep understanding of energy transfer mechanisms are critical for the development of advanced luminescent materials Our analysis of the Commission de l ' Eclairage (CIE) chromaticity coordinates reveals enhanced energy transfer dynamics in rare -earth -doped borates, facilitating the tuning of luminescent properties. These results not only deepen our understanding of the fundamental physics governing such phosphors but also open pathways for the development of optoelectronic applications requiring consistent color output, such as LED technologies and solid-state lighting.Öğe Novel Tb3+-Doped LaAl2 B4 O10 phosphors: Structural analysis, luminescent properties, and energy transfer mechanism(Pergamon-Elsevier Science Ltd, 2024) Kaynar, U. H.; Aydin, H.; Hakami, Jabir; Altowyan, Abeer S.; Coban, M. B.; Ayvacikli, M.; Canimoglu, A.This study explores the structural and luminescent properties of terbium (Tb3+)-doped lanthanum aluminium borate (LaAl2B4O,0, abbreviated as LAB) phosphors, a novel host lattice for Tb3+ doping. LAB:Tb3+ phosphors, with varying dopant concentrations, were synthesized using a microwave-assisted combustion synthesis approach and characterized using X-ray diffraction (XRD), Rietveld refinement, and photoluminescence spectroscopy at both room and low temperatures. The structural analysis confirmed the hexagonal crystal structure of LAB and revealed successful incorporation of Tb3+ ions without altering the fundamental lattice. Luminescence studies demonstrated that the LAB:Tb3+ phosphors show strong green emission primarily attributed to the 5D4 -> 7F5 transition of Tb3+. The optimal doping concentration was determined to be 5 wt% Tb3+, which provided maximum luminescence efficiency. This concentration also allowed for a critical study of energy transfer mechanisms within the phosphor, revealing dipole-dipole interactions with a critical distance of 9.80 & Aring; between Tb3+ ions. Additionally, the CIE chromaticity coordinates of LAB:0.05 Tb3+ were precisely determined to be (0.289, 0.4460), indicating the potential for high-quality green emission suitable for solid-state lighting and display technologies. This work not only demonstrates the potential of LAB:Tb3+ as a highly efficient green luminescent material, but also sheds light on the mechanisms responsible for energy transfer and concentration quenching.Öğe Synthesis and enhanced photoluminescence of the BaSiF6:Dy3+ phosphors by Li+ doping via combustion method(Elsevier, 2022) Souadi, G.; Kaynar, U. H.; Ayvacikli, M.; Canimoglu, A.; Can, N.Undoped BaSiF6, Dy3+ doped BaSiF6, and Dy3+, Li+ co-doped BaSiF6 phosphors were synthesized through a gelcombustion method. The prepared samples were characterized by powder x-ray diffraction (XRD), Fourier transform infrared (FTIR), energy dispersive x-ray spectroscopy (EDS), and photoluminescence (PL) techniques. The XRD data revealed that both the Dy3+ doped and Li+ co-doped BaSiF6 phosphors exhibited a single-phase structure belonging to the space group R (3m) over bar which matched well with the standard JCPDS files (No. 002-6613). FTIR spectra showed absorption bands at 3417 cm -1 , 1640 cm(-1), and 1620 cm(-1) corresponding to water molecules. EDS analysis confirmed the chemical composition of the prepared samples. The PL emission spectra of BaSiF6:Dy3+ by different co-doping concentrations of Li+ exhibited prominent emission peaks at 490 nm, 572 nm, 672 nm and 758 nm. The incorporation of Li+ is beneficial for enhancing the photoluminescence intensity. The optimum Li+ amount was 8% for BaSiF6:Dy3+ and then started to decrease. The enhancement could be due to the occurrence of oxygen vacancies due to the incorporation of Li+ ions. The x = 0.301 and y = 0.361 coordinates of this phosphor with varying Li+ dopant concentration determined by the Commission Internationale de l'Eclairage (CIE - 1931) were in the white range. The present work demonstrates how a simple and effective method can be used to prepare novel nanophosphors for applications in the field of visible light emitting devices with enhanced white emission.Öğe Synthesis and photoluminescence characteristics of a novel Eu and Tb doped Li2MoO4 phosphor(Pergamon-Elsevier Science Ltd, 2021) Souadi, G.; Kaynar, U. H.; Ayvacikli, M.; Coban, M. B.; Oglakci, M.; Canimoglu, A.; Can, N.Li2MoO4:x Eu3+ and Li2MoO4:xTb(3+) phosphors, where x = 0.5, 1, 2, 3, 5 and 7 wt%, were synthesized through a gel-combustion method. The XRD data reveals that Eu3+ and Tb3+ doped Li2MoO4 phosphors exhibit a Rhombohedral structure belonging to the space group R3 which matched well with the standard JCPDS files (No.0120763). We present photoluminescence (PL) spectra from Eu and Tb doped Li2MoO4 under 349 nm Nd:YLF pulses laser excitation over the temperature range of 10-300 K. Undoped Li2MoO4 shows a wide broad band around 600 nm because of the intrinsic PL emission of tetrahedral of MoO42- which was in good agreement with previous findings. Under the excitation of 394 nm, the as-synthesized phosphors exhibited sharp and strong intensity PL emission signals in the red (612 nm, D-5(0) -> F-7(2) transition) and green (544 nm, D-5(4) -> F-7(5) transition), respectively. The critical doping concentration of Eu3+ and Tb3+ ions in the Li2MoO4 were estimated to be 2 wt%. The concentration quenching phenomena were discussed, and the critical distances for energy transfer have also been evaluated by the concentration quenching.Öğe Thermoluminescence behaviour of europium doped magnesium silicate after beta exposure(Elsevier, 2020) Ucar, Z. G. Portakal; Kaynar, U. H.; Dogan, T.; Souadi, G. O.; Ayvacikli, M.; Canimoglu, A.; Topaksu, M.This article presents a detailed analysis of beta ray exposed thermoluminescence response of a series of Eu3+ doped (0.5-10 mol%) Mg2SiO4 nanocrystalline samples successfully synthesized through solid state reaction method. Optimizing the doping concentration of Eu3+ ion in Mg2SiO4 phosphor was found as 3 mol%. Two main peaks were seen at 246 degrees C and 374 degrees C and also low temperature peak at 78 degrees C. The intensities of these peaks were increased linearly with increasing beta absorbed dose. T-m-T-stop method was used to reveal trap levels. Variable heating rate and computerized glow curve deconvolution methods were also used to evaluate the number of peaks and kinetic parameters, namely activation energy and frequency factor. The results of a series of experiments carried out to investigate some fading characteristics of Mg2SiO4:Eu3+ were also presented. The findings suggest that thermoluminescence properties of Mg2SiO4:Eu(3+ )makes this material suitable and promising dosimetric phosphor material for medical applications.Öğe Thermoluminescence characteristics of a novel Li2MoO4 phosphor: Heating rate, dose response and kinetic parameters(Pergamon-Elsevier Science Ltd, 2022) Souadi, G.; Kaynar, U. H.; Oglakci, M.; Sonsuz, M.; Ayvacikli, M.; Topaksu, M.; Canimoglu, A.Lithium molybdate (Li2MoO4) phosphor was synthesized by a gel combustion method and its thermoluminescence properties were studied with the irradiation of beta. Various Heating Rate (VHR), Initial Rise (IR), and Computerized Glow Curve Deconvolution (CGCD) methods were used to determine the kinetic parameters (activation energy E (eV), frequency factor s (s(-1)), and kinetic order b) of the visible glow peaks. According to the kinetic study, the TL glow curve is made up of seven separate peaks with activation energies of 1.05, 0.76, 0.40, 0.60, 0.78, 1.81 and 1.25 eV and these peaks follow general-order kinetics. The results clearly showed that undoped Li2MoO4 has a potential to be considered in dosimetric applications where high doses have to be monitored as in the case of clinical dosimetry.Öğe Thermoluminescence properties of beta particle irradiated Ca3Al2O6 phosphor relative to environmental dosimetry(Elsevier, 2020) Bakr, M.; Portakal-Ucar, Z. G.; Yuksel, M.; Kaynar, U. H.; Ayvacikli, M.; Benourdja, S.; Canimoglu, A.Undoped Ca3Al2O6 phosphor was successfully synthesized through a gel-combustion method using different fuels. It was characterized by X-ray diffraction (XRD) technique and its cubic phase structure was confirmed from XRD pattern. TL data were recorded from room temperature (RT) to 500 degrees C in the heating rate of 2 degrees C/s. The glow curves of Ca3Al2O6 sample exposed to different beta doses (0-200 Gy) exhibited a significant glow peak at about 184 degrees C. The TL intensity of the glow peak exhibited very good linearity between 0.1 and 10 Gy. Following this, it was decreased at higher doses which was referred to this effect as monotonic dose dependence. Initial rise (IR), peak shape (PS), and variable heating rate (VHR) methods were used to estimate trapping parameters. Computerized glow curve deconvolution (CGCD) method via TLAnal software was also applied to estimate the number of peaks and kinetic parameters corresponding to the main glow curve in Ca3Al2O6 sample. The trapping activation energy of the main dosimetric peak was calculated to be around 1.30 eV for all methods. Present findings confirm that Ca3Al2O6 host is a promising candidate for applications in environmental dosimetry as one depicts good TL dose response with adequate sensitivity and linearity.
