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Öğe Dy3+and Eu3+co-activated gadolinium aluminate borate phosphor: Synthesis, enhanced luminescence, energy transfer and tunable color(Pergamon-Elsevier Science Ltd, 2023) Madkhali, O.; Kaynar, Umit H.; Kaynar, S. Cam; Ayvacikli, M.; Can, N.The synthesis of GdAl3(BO3)4 phosphors incorporated with activators of Dy3+ and Dy3+/ Eu3+was successful and achieved through the gel combustion method. Powder X-ray diffraction (XRD) was employed to identify phase purity and the effects of dopant concentration on the crystallographic structure. The results of Photo-luminescence (PL) measurements revealed that the intensity and lifetime of luminescence properties varied depending on the concentrations of Dy3+ and Eu3+ ions. The dependence of luminescence intensity on doping concentration is investigated with respect to the energy transfer process between Eu3+ and Dy3+ ions. A decrease in luminescence lifetime occurs with increasing concentrations of Eu3+ co-doping. The energy transfer was also investigated using decay curve analysis. The co-doping of Eu3+ significantly boosts the energy transfer efficiency from 26% to 84%. These findings make GdAl3(BO3)4: Dy3+, Eu3+ phosphors an ideal choice for LED applications in solid state lighting and displays.Öğe High temperature photoluminescence dependence and energy migration of Tb3+-Incorporated K3Y(BO2)6 phosphors(Pergamon-Elsevier Science Ltd, 2024) Souadi, G.; Hakami, O.; Kaynar, U. H.; Coban, M. B.; Aydin, H.; Madkhali, O.; Zelai, T.This study investigates the structural and photoluminescence (PL) characteristics of Tb3+-incorporated K3Y(BO2)(6) (KYBO) phosphors synthesized via a microwave-assisted sol-gel technique. X-ray diffraction (XRD) and Rietveld refinement confirmed the formation of a pure hexagonal phase, with lattice expansion due to Tb3+ doping. PL studies revealed strong green emissions centered at 541 nm, attributed to the D-5(4) -> F-7(5) transitions of Tb3+ ions, with the highest intensity observed at 5 wt% Tb3+. A decrease in emission was observed at higher concentrations due to concentration quenching. Temperature-dependent PL measurements revealed reverse thermal quenching enhancing PL intensity. Chromaticity analysis based on CIE 1931 coordinates showed stable green emission across all concentrations, with a maximum color purity of 89.74% observed for the KYBO:3 wt% Tb3+ sample. The results, along with reverse thermal quenching behavior observed between 470K and 550K, suggest that these phosphors exhibit excellent potential for lighting and display technologies.Öğe Structural and temperature dependence luminescence characteristics of RE (RE=Eu3+, Dy3+, Sm3+and Tb3+) in the new gadolinium aluminate borate phosphor(Elsevier Sci Ltd, 2023) Madkhali, O.; Kaynar, Umit H.; Alajlani, Y.; Coban, M. B.; Guinea, J. Garcia; Ayvacikli, M.; Pierson, J. F.GdAl3(BO3)4:Dy3+, Sm3+, Eu3+, and Tb3+ samples were successfully achieved via a sol-gel combustion method. The observed XRD analysis confirms the formation of the desired GAB host, indicating rhombohedral structures that agree well with JPCD card number 72-1985. The FTIR analyses show the detection of B -O stretching and B -O -B bending modes as well as Al -O and Gd -O bonds in the phosphor samples. Energy dispersive spectroscopy (EDS) analysis reveals that Sm, Eu, Dy, and Tb have been successfully doped into GdAl3(BO3)4. The observed broad intrinsic luminescence band can be caused by oxygen-induced luminescence defects in the GAB host with hydrous precursors. The luminescence properties of rare earth ion-doped GdAl3(BO3)4 samples are analysed by photoluminescence spectra, showing their optimal doping concentrations and critical distances of Dy3+, Eu3+, Sm3+ and Tb3+ are 2 wt% -25.8 angstrom, 7 wt% -17 angstrom, 1 wt% -32.59 angstrom, and 7 wt% -17.03 angstrom. Additionally, the energy transfer mechanism for luminescence quenching was determined as dipole-dipole (for Dy3+, Eu3+, and Tb3+) or dipole-quadrupole (for Sm3+) and the cross-relaxation process. GdAl3(BO3)4 samples obtained by doping with different RE3+ ions exhibit intense light emissions with different colors originating from different RE3+ ions under 349 nm excitation. When doped with different concentrations of RE3+ ions, the luminescence properties of the samples changed. The synthesized luminescence materials have potential ap-plications in lighting and display technologies.Öğe Thermoluminescence behaviour and kinetic analysis of a novel Tb3+-Doped LaCa4O(BO3)3 phosphor: Impacts of heating rates and dose(Elsevier Sci Ltd, 2025) Madkhali, O.; Bulcar, K.; Barad, A.; Zelai, T.; Souadi, G.; Alathlawi, Hussain J.; Kaynar, U. H.This study employs kinetic analysis methods to comprehensively understand the thermoluminescence (TL) behaviour of Tb3+-doped LaCa4O(BO3)3 ( LACOB ), applying the Hoogenstraaten and Booth-Bohun-Parfianovitch methods, as well as the T m-T stop and Glow Curve Deconvolution (GCD) techniques. Optimal TL intensity was found at a Tb3+concentration of 2 wt%, beyond which concentration quenching occurred. The complete TL glow curve before preheating displays two peaks at approximately 70 degrees C and 286 degrees C. After preheating, only the 286 degrees C peak remains, due to its greater stability and intensity, making it the primary TL peak relevant for dosimetric applications. As the heating rate increased, the TL glow peaks shifted to higher temperatures and exhibited reduced intensity due to thermal quenching. The TL intensity exhibited superlinear behaviour at lower doses (0.5-20 Gy), followed by nearly linear behaviour at intermediate doses (30-100 Gy), and sublinear behaviour at higher doses. Anomalous fading of the TL signal was observed in LACOB:2 wt%Tb, suggesting competition with radiationless transitions. Activation energy values derived from Hoogenstraaten and Booth-Bohun-Parfianovitch methods showed close alignment, supporting the reliability of the kinetic analysis. The T m-T stop and GCD analyses with preheating identified four distinct TL glow peaks, with activation energies between 1.72 and 1.82 eV. Analysis whole glow curve revealed nine TL glow peaks overall, ranging from 1.08 to 1.82 eV, reflecting a complex trap structure with continuous energy distributions. The GCD method yielded a Figure of Merit (FOM) of 2.67 % with preheating and 2.84 without preheating, indicating a strong fit between experimental and theoretical data in both cases. The material demonstrated excellent stability and reusability, making it a strong candidate for dosimetric applications.Öğe Undoped and Eu doped LaCa₄O(BO₃)₃ phosphors: Thermoluminescence characteristics with a focus on kinetic parameters, anomalous heating rate, and dose response(Elsevier Ltd, 2025) Bulcar, K.; Portakal-Uçar, Z.G.; Zelai, T.; Souadi, G.; Hakami, O.; Kaynar, U.H.; Madkhali, O.The thermoluminescence (TL) properties of LaCa₄O(BO₃)₃ (LACOB) phosphors, both undoped and doped with 0.5 % Eu³⁺, were synthesized using a microwave-assisted sol-gel method and analysed under beta irradiation doses ranging from 0.1 Gy to 700 Gy. The TL glow curves revealed prominent peaks at 100 °C and 285 °C for the Eu-doped sample. Activation energy values were calculated using the Hoogenstraaten and Booth-Bohun-Parfianovitch methods, yielding 1.52 eV and 1.48 eV for the undoped sample, and 2.07 eV and 2.01 eV for the Eu-doped sample, respectively. Eu³⁺ ions introduced deeper traps and enhanced the thermal stability of the material. Anomalous increases in TL intensity with rising heating rates were observed, deviating from typical thermal quenching behaviour; this phenomenon was explained using a semi-localized transition (SLT) model. The TL reusability measurements demonstrated a standard deviation of less than 5 %, indicating consistent and reliable performance across multiple cycles. The TL glow curve deconvolution identified six distinct peaks in the undoped sample, while the Eu-doped sample showed a more complex trap structure with eight peaks, indicating the introduction of additional or modified trapping sites by Eu doping. The figure of merit (FOM) values obtained from the deconvolution analysis were all below 2.5 %, indicating a good fit between the observed and fitted TL signals. These findings suggest that Eu³⁺-doped LACOB is a robust material for radiation dosimetry, with its enhanced sensitivity, stability, and versatility across various dosimetric applications. © 2024 Elsevier Ltd and Techna Group S.r.l.
