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    Effects of dopant rate and calcination parameters on photoluminescence emission of Y2O3:Eu3+ phosphors: A statistical approach
    (Elsevier Sci Ltd, 2019) Ünal, Fatma; Kaya, Faruk; Kazmanli, Kursat
    In this study, Y2O3:Eu3+ phosphorescent powders with different dopant rates were synthesized by sol-gel method. Statistical experimental design methods were used to investigate the effects of calcination temperature (800, 900 and 1200 degrees C), time (5 and 7 h) and dopant rate (5 and 7% at.) on the colour of the photoluminescence emission. The XRD results showed that as-prepared powders were amorphous. After calcination, the crystal structures became cubic bixbyite-type. XRD and Raman spectroscopy results confirmed the existence of Eu3+ in the Y2O3 crystal. Crystallite sizes and lattice parameters of the powders were calculated by using Williamson-Hall and Cohen-Wagner methods, respectively. Photoluminescence emission spectra of the samples were measured at room temperature by using an optical emission spectroscope with 380 nm monochromatic excitation source and the emission spectra were transformed to CIELab colour space coordinates. The emission spectra exhibited a strong characteristic peak at 611 nm and a smaller peak at 614 nm. Depending on the dopant rate and the calcination parameters, other smaller peaks appeared at 587, 592, 606, 623 and 631 nm. The CIELab colour space transformation results showed that the powders possessed orange-red emission. The dopant rate and the calcination conditions slightly changed the emission colour. According to the statistical analysis, the dopant rate had the strongest effect on a* colour space value (redness) whereas all parameters had equally significant effect on b* colour space value (yellowness). The ANOVA analysis revealed that the interaction between the temperature and the dopant rate was also statistically significant with the confidence level of 95%. This interaction was attributed to the relation between lattice strain and calcination temperature, which confirms the strong symmetry dependence of the electron-dipole (ED) transitions of the Y2O3:Eu3+ phosphors.
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    Öğe
    Modelling of relation between synthesis parameters and average crystallitesize of Yb2O3 nanoparticles using Box-Behnken design
    (Elsevier, 2020) Ünal, Fatma; Kaya, Faruk
    A straightforward wet chemical method has been applied for the fabrication of Yb2O3nanoparticles (NPs) fromytterbium nitrate solution by using ammonium carbonate as precipitation agent. Effects of precursor molarity(0.1, 0.15 and 0.2 M), calcination temperature (800, 900 and 1000 °C) and time (2, 4 and 6 h) on averagecrystallite size (CS) of the NPs were statistically investigated by using Box-Behnken design. A simple and ef-fective quadratic model was proposed for controlling the CS. The CS values were calculated by using WilliamsonHall method (W-H) from X-Ray Diffraction (XRD) broadening data and found to be ranging between 13 and26 nm. Agglomerated NPs morphologies and particle sizes were revealed by Field Emission Gun-ScanningElectron Microscopy (FEG-SEM). Fourier Transform Infrared (FTIR) spectrophotometry confirmed that as-re-ceived Yb2(CO3)3xH2O powders were successfully transformed into Yb2O3NPs with calcination. High-ResolutionTransmission Electron Microscopy (HRTEM) results verified the average CS values. ANOVA analyses revealedthat linear and squared terms of the production parameters were significantly related to the CS whereas in-teraction terms were insignificant with the confidence level of 95% (R2= 92.67%, R2-adj = 87.17%). Thecalcination temperature had the highest impact on the average CS followed by the time and precursor molarity.Increasing calcination parameters resulted in bigger crystallites whereas increasing precursor molarity exhibiteda critical supersaturation value (0.15 M) from which the average CS was decreased
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    Öğe
    Synthesis, characterization and radioluminescence properties of erbium-doped yttria phosphors
    (Springer, 2021) Ünal, Fatma; Kaya, Faruk; Kazmanlı, Kürşat
    Radioluminescence (RL) behaviour of erbium-doped yttria nanoparticles (Y2O3:Er3+ NPs) which were produced by sol-gel method was reported for future scintillator applications. NPs with dopant rates of 1at%, 5at%, 10at% and 20at% Er were produced and calcined at 800 degrees C, and effect of increased calcination temperature (1100 degrees C) on the RL behaviour was also reported. X-ray diffraction (XRD) results showed that all phosphors had the cubic Y2O3 bixbyite-type structure. The lattice parameters, crystallite sizes (CS), and lattice strain values were calculated by Cohen-Wagner (C-W) and Williamson-Hall (W-H) methods, respectively. Additionally, the optimum solubility value of the Er3+ dopant ion in the Y2O3 host lattice was calculated to be approximately 4at% according to Vegard's law, which was experimentally obtained from the 5at% Er3+ ion containing solution. Both peak shifts in XRD patterns and X-ray photoelectron spectroscopy (XPS) analyses confirmed that Er3+ dopant ions were successfully incorporated into the Y2O3 host structure. High-resolution transmission electron microscopy (HRTEM) results verified the average CS values and agglomerated NPs morphologies were revealed. Scanning electron microscopy (SEM) results showed the neck formation between the particles due to increased calcination temperature. As a result of the RL measurements under a Cu K-alpha X-ray radiation (wavelength, lambda = 0.154 nm) source with 50 kV and 10 mA beam current, it was determined that the highest RL emission belonged to 5at% Er doped sample. In the RL emission spectrum, the emission peaks were observed in the wavelength ranges of 510-575 nm (H-2(11/2), S-4(3/2)-I-4(15/2); green emission) and 645-690 nm (F-4(9/2)-I-4(15/2); red emission). The emission peaks at 581, 583, 587, 593, 601, 611 and 632 nm wavelengths were also detected. It was found that both dopant rate and calcination temperature affected the RL emission intensity. The color shifted from red to green with increasing calcination temperature which was attributed to the increased crystallinity and reduced crystal defects.