Browsing by Author "mustafa ilhan"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Evaluation of the Structural, Near-Infrared Luminescence, and Radioluminescence Properties of Nd3+ Activated TTB-Lead Metatantalate Phosphors
    (2023) İlker Çetin KESKİN; mustafa ilhan
    The study reports the structural and spectroscopic properties of Nd3+ doped lead metatantalate phosphor series fabricated by conventional solid state method. XRD results of the PbTa2O6 phase confirm the tungsten bronze symmetry and single-phase structure between 0.5 and 10 mol% Nd3+ concentrations. The lead decrease in the structure can be associated with maintaining the charge balance and single phase due to evaporation during sintering. In SEM micrographs, the grains exhibited shapeless morphology, and the grain sizes varied from 0.5 to 7 m. In EDS results, the increase of Ta/Pb ratio in grain surfaces indicated some lead evaporation, as reported in previous studies. The absorption spectrum of PbTa2O6 host peaked around 275-280 nm, and the band gap was found to be 3.7±0.2 eV. The absorptions of Nd3+ doped phophors shifted the high wavelenght or the low band gap, where the band gaps were found between 3.1±0.2 and 3.3±0.2 eV. The PL emissions of the phosphors in near-inrared region were observed with the transitions of 4F3/2→4I9/2 (at 875 nm) and 4F3/2→4I11/2 (at 1060 nm) of Nd3+. The RL emissions or X-ray excited luminescence were monitored with the transitions of 4F3/2→4I9/2 (at 875 nm), 4F3/2→4I11/2 (at 1065 nm) in the infrared region, and the transitions of 2F(2)5/2→4F9/2, 2F(2)5/2→2H(2)11/2, 2F(2)5/2→4G5/2, 2F(2)5/2→4G7/2, 2F(2)5/2→4G9/2 in the visible region corresponding to at around 430, 455, 490, 525, and 570 nm, respectively. PL and RL emissions of the phosphors exhibited the decreasing emission intensity over 5 mol% due to the concentration quenching which may be associated with cross-relaxing mechanism. In the PL and RL spectral profiles, the similarity of splitting levels was attributed to the similarity of the local symmetry of the ligand ions surrounding the Nd3+ ion. The CIE coordinates obtained using RL emissions were found close to the blue region due to visible region transitions.
  • No Thumbnail Available
    Item
    Structural and Dielectric Properties of RE3+, B3+ co-doped (RE3+=Sm3+, Dy3+) BaTa2O6 Tetragonal Tungsten Bronze-Type Ceramics
    (2024) mustafa ilhan; Mehmet İsmail KATI; Lutfiye feray Guleryuz
    In this paper, the effect of boron doping on dielectric properties was investigated using BaTa2O6:xSm3+, yB3+ (x=5 mol%, y= 0, 5, 15, 30, 50, 70, 100 mol%) and BaTa2O6:xDy3+, yB3+ (x=10 mol%, y= 0, 5, 15, 30, 50, 70, 100 mol%) tungsten bronze ceramics fabricated by the conventional solid-state synthesis. XRD (X-ray diffraction) results revealed a single BaTa2O6 phase with space group P4/mbm (127) for both series. Additionally, in both series, there was an increase in crystallite sizes and cell parameters with increasing B3+ concentration. SEM (scanning electron microscopy) examinations indicated that the increase of boron promoted grain growth and grain elongation. In impedance results, in both series, increasing boron concentration up to 100 mol% increased the dielectric constant. Moreover, the presence of boron was associated with a relaxing transition in the B-site substitution of RE3+ (RE=Sm, Dy) ions and a contribution to the dielectric permittivity, while the increase in tetragonality or c/a ratio for both series was ascribed to the increase in the ferroelectric Curie temperature. In both series, a decrease in dielectric loss (tan δ) occurred, which was explained by the increasing sintering temperature effect with increasing boron, reducing the mobility of oxygen vacancies.
  • No Thumbnail Available
    Item
    Evaluation of Structural and Dielectric Properties of Eu3+, B3+ co-doped Ba2GdMO6 (M=Nb, Ta) Double Perovskite Ceramics
    (2024) mustafa ilhan; Lutfiye feray Guleryuz
    In the study, the structural and dielectric properties of Ba2GdMO6 (M=Nb, Ta) double perovskite ceramics produced with solid-state method were examined by co-doping xEu3+ and yB3+ (x=10 mol%, y=0, 5, 15, 30, 50, 70 and 100 mol%). XRD (X-ray diffraction) results of the ceramic samples exhibited a single-phase structure with cubic symmetry Fm-3m space group, while increasing B3+ concentration led to an increase in crystallite sizes and lattice parameters up to 50 mol% in both series. SEM (scanning electron microscopy) examinations revealed the presence of boron-supported grain growth and agglomeration in the grains of both series, and also a slight angularity occurred in grain shape at high B3+ concentrations. The dielectric constant (ε') of the ceramic samples in both series increased with increasing boron concentration up to 50 mol%, and it was approximately 33.5 and 35.4 at 20 Hz for the Ba2Gd1-xNbO6:xEu3+, yB3+ and Ba2Gd1-xTaO6:xEu3+, yB3+, respectively. The decrease in the dielectric constant after 50 mol% may be attributed to the presence of increased strain in the structure, as shown by the decrease in crystallite size. The increasing B3+ concentration caused a decrease in dielectric loss (tan δ) in both series, which was attributed to the suppression of oxygen vacancies due to the increased presence of B3+ and hence to a decrease in ionic conductivity and dielectric loss.