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    Adsorption of thorium (IV) ions by metal ion doped ZnO nanomaterial prepared with combustion synthesis: Empirical modelling and process optimization by response surface methodology (RSM)
    (Pergamon-Elsevier Science Ltd, 2021) Kaynar, Ümit H.; Kaynar, S. Cam; Karalı, E. Ekdal; Ayvacıklı, M.; Can, N.
    Environmental problems have reached enormous dimensions, driving efforts to remove and recycle waste from energy and industrial production. In particular, removing the radionuclide contamination that occurs as the nuclear industry grows is difficult and costly, but it is vital. Technologic and economical methods and advanced facilities are needed for the separation and purification of radioactive elements arising from the nuclear industry and uranium and thorium mining. With the adsorption method, which is the most basic separation and recovery method, the use of high-capacity nanomaterials has recently gained great importance in reducing the activity of the waste, reducing its volume by transforming it into solid form, and recovering and removing liquid radioactive wastes that might harm the ecological environment. This study aimed to determine the adsorption properties of metal ion-doped nano ZnO (nano-ZnO:Al) material synthesized by the microwave-assisted gel combustion method for the adsorption of thorium (IV) from aqueous media. First, characterization processes such as XRD, SEM, BET and zeta potential were performed to observe changes in the host ZnO adsorbent structure caused by the doping process. Later, this was optimized via the response surface method (RSM), which is widely used in the characterization of the adsorption properties of thorium (IV) from aqueous solutions. Such characterization is commonly used in industrial research. We tested how pH (3-8), temperature (20-60 degrees C), Th (IV) concentration (25-125 mg/L) and adsorbent amount (0.01-0.1 g) affect adsorption efficiency. The best possible combinations of these parameters were determined by RSM. It was calculated by RSM that the design fits the second order (quadratic) model using the central composite design (CCD) for the design of experimental conditions. R-2 and R-2 adjusted values from the parameters showing the model fit were 0.9923 and 0.9856, respectively. According to the model, the experimental adsorption capacity was 192.3 mg/g for the doped-ZnO nanomaterial under the theoretically specified optimum conditions. Also, the suitability of Th (IV) adsorption to isotherms was examined and thermodynamic parameters were calculated.
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    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.
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    Influence of laser excitation power on temperature-dependent luminescence behaviour of Ce- and Tb-incorporated BaMgAl10O17 phosphors
    (Pergamon-Elsevier Science Ltd, 2020) Kaynar, Ümit H.; Kaynar, S. Cam; Ayvacıklı, M.; Karabulut, Y.; Souadi, G. O.; Can, N.
    BaMgAl10O17 (BAM) is a highly suitable host lattice for various rare earth ions with excellent luminescence properties in different spectral regions, including a strong photoluminescence (PL) emission from the visible spectral region. A new Ce- and Tb-incorporated BaMgAl10O17 phase was synthesized successfully using a wet combustion method and it was studied as a function of the temperature and laser excitation power. We further characterize the obtained phosphors with X-ray diffraction at room temperature. Different fuel/oxidant (f/o) ratios were introduced to investigate the optimum synthesis conditions for the BAM phosphors and optimum ratio was found out to be 8. The photoluminescence (PL) spectra were collected under the excitation light generated by a Nd:YLF pulse laser at 349 nm as the temperature was increased from 10 K to 300 K. A strong green emission of Tb3+ was observed in the green region of the spectrum due to the D-5(4)-> F-7(J) transition. We also observed a wide emission band from the Ce3+ ion in the wavelength range of 350-650 nm. The luminescence intensities of all phosphors exhibited different patterns with an increase in the temperature. We also evaluated how the PL spectrum of the rare earth-activated BAM host matrix shifts under various laser excitation powers. The PL intensity of Ce-activated BAM significantly shifted (similar to 30 A) to the blue region of the spectrum with an increase in the laser excitation power, however we did observed no shift forTb(3+) activated BAM. The present findings suggest that Tb-incorporated BaMgAl10O17 can be effective as a green phosphor candidate material with a wide range of applications.