Browsing by Author "Portakal Z.G."
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Item Luminescence characteristics of Dy3+ incorporated zinc borate powders(Elsevier B.V., 2017) Portakal Z.G.; Dogan T.; Yegen S.B.; Küçük N.; Ayvacikli M.; Guinea J.G.; Canimoglu A.; Karabulut Y.; Topaksu M.; Can N.We have synthesized powder samples of Dy3+ doped zinc borates by nitric acid method. X-ray diffraction (XRD) and environmental scanning electron microscope (ESEM) techniques were utilized to examine the structure and morphological observation of the samples. Luminescence characteristics of the samples were investigated using room temperature (RT) cathodoluminescence (CL) and radioluminescence (RL) measurements under excitation with electron beam and X-rays, respectively. The presence of small amounts of Dy3+ incorporated in the host lattice does not affect the structure of the prepared samples remarkably. The CL and RL spectra showed the characteristic emissions of Dy3+(magnetic dipole transition of 4F9/2 →6H11/2 Blue; forced electric dipole transition of 4F9/2→ 6H13/2 Yellow; 4F9/2 →6H11/2 Red; 4F9/2 →(6H9/2 +6H11/2) infrared). Thermoluminescence (TL) method was also conducted to determine the effects of various concentrations of Dy3+ on the TL properties of ZnB2O4. The TL glow peak of beta irradiated ZnB2O4:Dy3+ phosphors is a well-defined and centered at around 96 °C with a constant heating rate of 2 °C/s. Initial rise method was employed to observed main TL glow curve for determining the activation energy (Ea) and the frequency factor (s). © 2017 Elsevier B.V.Item Doping Sm3+ into ZnB2O4 phosphors and their structural and cathodoluminescence properties(Elsevier Ltd, 2018) Kucuk N.; Bulcar K.; Dogan T.; Garcia Guinea J.; Portakal Z.G.; Karabulut Y.; Ayvacikli M.; Canimoglu A.; Topaksu M.; Can N.In this study, ZnB2O4:xSm3+ (0.01 ≤ x ≤ 0.05 mol) powder phosphors have been synthesized by low temperature chemical synthesis method. The structure and morphological observation of the phosphor samples were systematically monitored by X-ray powder diffraction (XRD) and environmental scanning electron microscope (ESEM) coupled to an energy dispersive X-ray spectrometer (EDS). The all diffraction peaks are well assigned to standard data card (PDF#39-1126). Emission properties of the samples were explored using light emission induced by an electron beam (i.e cathodoluminescence, CL) at room temperature (RT). When excited with electron beam, CL spectral measurements of scrutinized phosphors exhibit orange-red luminescence at 572 nm, 606 nm and 658 nm due to various transition from ground state to 6H5/2,6H7/2 and 4G5/2 states, respectively. The transition 4G5/2 → 6H7/2 located at 606 nm can occur as hypersensitive transition having the selection rule ΔJ = ±1. The observed peaks are in the region of yellow reddish light of Sm3+. Experimental results verify that the optimum Sm3+ content in terms of intense luminescence for this series of phosphors was 2%. Beyond 2% of Sm3+ ions concentration, luminescence quenching occurs due to an enhanced probability of the energy transfer from one Sm3+ to another that matches in energy via cross-relaxation and dipole-dipole interactions according to Dexter theory. A suitable energy transfer model between two adjacent Sm3+ ions in the ZnB2O4 phosphors was accomplished by the electric dipole-dipole interaction. The critical transfer distance (Rc) for non-radiative energy transfer was found to be 21.52 Å at 2 mol % Sm3+ doped ZnB2O4. Additionally, thermoluminescence (TL) glow curves of undoped and Sm activated ZnB2O4 under beta irradiation of 10 Gy are also discussed here. © 2018 Elsevier B.V.Item Thermoluminescence properties of Tb doped Mg2SiO4 after beta irradiation(Elsevier B.V., 2019) Akça S.; Portakal Z.G.; Dogan T.; Kucuk N.; Canimoglu A.; Topaksu M.; Can N.In this study, we performed Thermoluminescence (TL) experiments to extract the trapping parameters and dosimetric properties of Tb-doped Mg2SiO4 phosphors. Glow peaks located at 193, 270, and 350 °C were observed in the glow curve but the peak at 193 °C was especially investigated as a dosimetric peak in this study. We also observed an anomalous heating rate effect in which the maximum TL intensity of the glow curve augmented with an increasing heating rate. The computerized glow curve deconvolution (CGCD) method, initial rise (IR) and Hoogenstraaten's method were used to determine the activation energies of associated trapping centers for both BSL-TL 365 nm and IRSL-TL wideband blue filters. The TL characteristics of this phosphor indicate that Mg2SiO4:Tb3+ could be a promising material for dosimetric applications. Efforts should be made to improve the fading behaviour by adding other activators as co-dopants. © 2019 Elsevier B.V.Item Thermoluminescence analysis of beta irradiated ZnB 2 O 4 : Pr 3+ phosphors synthesized by a wet-chemical method(Elsevier Ltd, 2019) Akca S.; Oglakci M.; Portakal Z.G.; Kucuk N.; Bakr M.; Topaksu M.; Can N.In this paper we describe the thermoluminescence (TL) characteristics of ZnB 2 O 4 :Pr 3+ phosphors with Pr concentrations varying between 0.2 and 1 mol% prepared by a wet-chemical method. The TL glow curves of the phosphor sample consisted of three peaks located at 71 °C (P1), 124 °C (P2) and 233 °C (P3). The TL intensity increased with the beta dose ranging from ∼0.1 to ∼20 Gy. Dose response, reproducibility and trapping parameters of TL glow curves were evaluated to clearly reveal thermoluminescence features. We observed that TL intensity of P2 and P3 peaks decreases as the heating rate increases. Trap parameters were estimated via the Hoogenstraaten, Booth-Bohun-Parfianovitch, the initial rise methods combined with T m −T stop experiment and TLanal CGCD program. Heating rates were varied to use in the Hoogenstraaten analyses. The T m −T stop investigations on regenerated TL signals for P1 and P2 peaks indicated that ZnB 2 O 4 :Pr 3+ phosphor has four electron trap levels with energy values in the range of 0.5–1.5 eV These four traps have first order kinetic and are formed at high temperature region. Resulting values are utilized as a reference for the CGCD procedure and the trapping parameters from the TL glow curves are calculated. The figure of merit (FOM) of the TL glow curve during curve fitting procedures is found to be 2.019%. The intensities of the main dosimetric peaks appeared at 124 °C and 233 °C exhibits good linear dose response up to 20 Gy. These results provide valuable knowledge for use of the characteristics of Pr doped ZnB 2 O 4 in dosimetry research, just need to eliminate low temperature TL peak. © 2019 Elsevier LtdItem A study on thermoluminescence behaviour of Eu doped LaB3O6 irradiated with beta particles(Elsevier Ltd, 2020) Halefoglu Y.Z.; Oglakci M.; Portakal Z.G.; Akca S.; Souadi G.O.; Canimoglu A.; Topaksu M.; Can N.Lantanium triborate (LaB3O6) samples doped with Eu3+ ions are synthesized via combustion route. This study primarily reports the thermoluminescence (TL) behaviour of LaB3O6 host. X-ray diffraction (XRD) pattern reveals that LaB3O6 exhibits a single phase matched with JCPDS card 98-002-3609. Dose response, reusability and trap parameters of TL glow curves are evaluated to clearly reveal the TL features. The results show that the peak positions of TL glow curves are affected by varying the concentration of Eu. The experimental results obtained from the dose-response of LaB3O6:Eu3+ (1%) which has given high TL intensity reveal that the intensity of TL given by the total area under glow curves shows a good linearity (b= 0.997) up to 20 Gy. In addition, the minimum detectable dose (MDD) value has been calculated as 1.45 mGy with a standard deviation of 0.8%. Main TL peak maxima is observed around 197 °C with heating rate (HR) of 2 °Cs−1. An anomalous HR effect is observed for this peak in the range of 0.5–20 °Cs−1 with beta dose of 5 Gy. To find the overlapping peak numbers and determine the kinetic parameters of the main peak of LaB3O6:Eu3+ (1%), Initial Rise (IR) method using Tm−Tstop experiment and CGCD analysis have been performed for HRs of 0.5 and 2 °Cs−1. It can be said that the results of the methods are in good agreement when same trap numbers (at least eight separate peaks for both) and close energy values are taken into consideration. Deconvolution procedure of LaB3O6: Eu3+(1%) is performed using general order kinetic equation by R studio ‘tgcd’. Additionally, the lifetimes of each deconvolved peaks by CGCD of Eu activated LaB3O6 (1%) have been calculated. Based on the results it can be put forth that TL characteristics of Eu doped LaB3O6 can be used as a promising material for thermoluminescence dosimetry-environmental applications. © 2019 Elsevier LtdItem Enhanced photoluminescence properties of Eu3+/Li+ co-doped ZrO2: A focus on red and far-red emissions(Elsevier B.V., 2025) Altowyan A.S.; Kaynar U.H.; Aydin H.; Coban M.B.; Portakal Z.G.; Akça-Özalp S.; Hakami J.; Ayvacikli M.; Topaksu M.; Can N.In this study, Eu3+ and Li+ co-doped ZrO2 nanophosphors were synthesized using a microwave-assisted gel combustion method. While the synthesis method ensures phase stabilization, it does not directly enhance photoluminescence (PL) intensity. Instead, the observed PL enhancement originates from Li+ co-doping, which improves charge compensation and modifies local symmetry. Structural analysis confirmed the stabilization of the tetragonal phase due to Li+ co-doping, which introduced controlled oxygen vacancies. These structural changes led to a 4.67-fold intensity enhancement in red emission at 611 nm (5D0 → 7F2 transition), and a 4.26-fold increase in far-red emission at 711 nm (5D0 → 7F4 transition). Optimal doping concentrations of Eu3+ (0.02) and Li+ (0.03) achieved the highest luminescence intensity while maintaining color purity values up to 88.71 %. High-temperature PL measurements revealed stable emission peaks up to 550 K, demonstrating the material's thermal stability despite intensity reductions due to thermal quenching. These findings establish Eu3+/Li+ co-doped ZrO2 nanophosphors as promising candidates for solid-state lighting, plant growth lighting, and optoelectronic applications requiring enhanced red and far-red emissions. © 2025 Elsevier B.V.