Browsing by Author "Akça-Özalp S."

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    Unravelling the impact of unusual heating rate, dose-response and trap parameters on the thermoluminescence of Sm3+ activated GdAl3(BO3)4 phosphors exposed to beta particle irradiation
    (Elsevier Ltd, 2023) Souadi G.; Kaynar Ü.H.; Sonsuz M.; Akça-Özalp S.; Ayvacikli M.; Topaksu M.; Ozmen O.T.; Can N.
    The thermoluminescence of GdAl3(BO3)4 (GAB) doped with various concentrations of Sm3+ (i.e. from 0.5 to 7 wt%), prepared by gel combustion, was studied. TL glow peaks at 78 °C and 225 °C are observed. The intensity of the glow peak at 225 °C increased with a faster heating rate. To gain insight into the trap activation energies, the methods of Hoogenstraaten and Booth-Bohun-Parfianovitch were used, where the calculated activation energies are 0.57 eV and 0.60 eV for Peak I and 1.69 eV and 1.71 eV for Peak II respectively. The dose-response of GAB:0.5 wt%Sm3+ demonstrates robust linearity up to 40 Gy, with a strong correlation coefficient of 0.999. Both TM-Tstop combined with the Initial Rise (IR) and Computerized Glow Curve Deconvolution (CGCD) techniques were employed, which revealed six overlapping glow peaks beneath the main peaks. Additionally, the results suggest that the TL signal can be efficiently exploited for radiation dosimetry applications. © 2023 Elsevier Ltd
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    Beta irradiation-induced thermoluminescence: Glow curve analysis and kinetic parameters in combustion-synthesized undoped Ca4YO(BO3)3
    (Elsevier Ltd, 2024) Madkhli A.Y.; Jabali D.A.; Souadi G.; Sonsuz M.; Kaynar U.H.; Akça-Özalp S.; Ayvacikli M.; Madkhali O.; Topaksu M.; Can N.
    This study examines the thermoluminescent (TL) properties of undoped Ca4YO(BO3)3 phosphor, focusing on how it behaves under a variety of experimental conditions. The IRSL-TL 565 nm was chosen as the appropriate detection filter among various optical detection filter combinations. During the preheating trials conducted at a rate of 2 °C/s, the TL peak exhibited increased intensity, particularly around 200 °C. The experimental outcomes demonstrated a reliable linear relationship (R2 = 0.996 and b = 1.015) in the dose response of undoped preheated Ca4YO(BO3)3 within the range of 1–200 Gy. The investigation encompasses a range of techniques, including the TM-Tstop method, computerized glow curve deconvolution (CGCD) analysis, and theoretical modelling. The application of the TM-Tstop method to samples irradiated with a 5 Gy dose revealed distinct zones on the TM versus Tstop diagram, signifying the presence of at least two discernible components within the TL glow curve, specifically, a single general order kinetics peak and a continuous distribution. The analysis of activation energy versus preheated temperature exhibited a stepwise curve, indicating five trap levels with depths ranging between 1.13 eV and 1.40 eV. The CGCD method also revealed the superposition of at least five distinct TL glow peaks. It was observed that their activation energies were consistent with the Tm-Tstop experiment. Furthermore, the low Figure of Merit (FOM) value of 1.18% indicates high reliability in the goodness-of-fit measure. These findings affirm the reliability and effectiveness of the employed methods in characterizing the TL properties of the Ca4YO(BO3)3 phosphor under investigation. Theoretical models, including the semi-localized transition model, were introduced to explain anomalous observations in TL glow peak intensities and heating rate patterns. While providing a conceptual framework, these models may require adjustments to accurately capture the specific characteristics uncovered through CGCD analysis. As a potential application, the study suggests that the characterized TL properties of Ca4YO(BO3)3 phosphor could be utilized in dosimetric applications, such as radiation dose measurements, owing to its reliable linear response within a broad dose range. © 2024 Elsevier Ltd
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    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.