Browsing by Author "Güleryüz, LF"

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    Effect of boron incorporation on the structural, morphological, and spectral properties of CdNb2O6:Dy3+phosphor synthesized by molten salt process
    Ilhan, M; Ekmekçi, MK; Güleryüz, LF
    The effect of boron addition on the structural, morphologic and spectral properties was investigated by using xDy3+ (x = 0.5, 3, 6 mol%) doped, and xDy3+, yB3+ (y = 0, 5, 15, 25 mol%) co-doped CdNb2O6 powders produced by molten salt method. X-ray diffractions (XRD) of all Dy3+ doped, and B3+, Dy3+ co-doped samples showed that they retained the single-phase structure. The homogeneous dissolution of the Dy3+ doping without forming an impurity phase in the structure can be attributed to the flux effect of the molten salt process and boron doping. Scanning electron microscopy (SEM) micrographs of the B3+, Dy3+ co-doped grains showed that the effect of boron promotes grain growth and prismatic-like grain shape. Photoluminescence (PL) emissions of the phosphors with the excitation of 351.9 nm were monitored by the 4F9/2 -> 6H15/2, 4F9/2 -> 6H13/2, and 4F9/ 2 -> 6H11/2 transitions. PL excitations and a broad peak at 275 nm originating from the O2--> Nb5+ band transition were observed with the emission of 577.9 nm. The PL emissions of Dy3+, B3+ co-doped phosphors increased about two fold compared to Dy3+ doped samples. The increase in PL may be related to the increased presence of luminescence centers at or near grain surface due to the decreasing surface area (SA)/volume (V) ratio as the growth of B3+ co-doped grains and the transformation from rod-like to prismatic-like shape. The increased Dy3+ presence led to a decrease in observed lifetime, while the B3+ increase did not cause any change. The study may provide a different perspective for the understanding and controlling of grain morphology and the luminescence relation for RE-doped phosphors.
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    Structural, morphological, spectral properties and high quantum efficiency of Eu3+, B3+co-activated double perovskite Ba2GdMO6 (M = Nb, Ta) phosphors
    Güleryüz, LF; Ihan, M
    The influence of boron on the structural, morphological, and spectral properties was examined using Ba2Gd1-xMO6 (M = Nb, Ta) double perovskite ceramics co-doped with xEu3+ and yB3+ (x = 10 mol%, y = 0, 5, 15, 30, 50, 70, 100 mol%), which were synthesized through the solid-state method. X-ray diffractions of all the samples revealed a single-phase structure, and SEM micrographs of B3+, Eu3+ doped grains showed that the flux effect of boron promotes grain growth. The optical band gap energy was calculated from UV-Vis reflectance spectra, where Eg values decreased between 0 and 100 B3+. PL emissions of phosphors increase up to 50 mol% B3+ concentration due to increasing grain size and improving crystallinity, while a somewhat increase occurred in the asymmetry ratio for both series. The increase of the Judd-Ofelt (JO) parameters (Omega 2 and Omega 4) with increasing B3+ was associated with the decreasing local symmetry of Eu3+ sites and the decreasing electron density in the ligands. Moreover, while the increase of boron improved the quantum efficiency of phosphors, the eta QE% values of 50 mol% B3+ concentration were 80.84 % and 98.02 % for Ba2Gd1-xMO6:xEu3+, yB3+ (M = Nb, Ta), respectively. The paper may provide an alternative perspective and a new strategy for the structural, morphology, and luminescence efficiency of RE3+-doped double perovskite phosphors.
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    Study on structural, morphological, and spectral properties of LiMPO4: Eu3+, B3+(M = Zn, Sr) phosphors and latent fingerprint applications
    Ilhan, M; Güleryüz, LF; Kati, MI
    Boron influences the melting point, crystallization, and both the optical and structural characteristics of ceramic materials. The effect of boron on the structural, morphological, and spectral properties for LiMPO4:xEu3+, yB3+ (where M = Zn or Sr and x = 3 mol%, y = 0-100 mol%) phosphors was investigated using materials fabricated with the solid-state method. In XRD results, LiZnPO4:Eu3+, B3+ series showed a single-phase structure up to 100 mol%, while LiSrPO4:Eu3+, B3+ samples exhibited a low monoclinic phase at low concentrations. In SEM micrographs, the flux effect of boron caused growth in LiMPO4:Eu3+, B3+ (M = Zn, Sr) grains sizes. As the B3+ concentration increases, PL emissions for both phosphor series increased up to 100 mol%, and the luminescence intensities increased over 8 times. Judd-Ofelt (JO) parameters (Q2, Q4) showed a slightly increasing trend for LiZnPO4:Eu3+, B3+, whilst the change in Q2 and Q4 parameters was limited for LiSrPO4:Eu3+, B3+ series. As the B3+ concentration increased, the observed lifetime (z) of LiZnPO4:Eu3+, B3+ with a bi-exponential decay decreased, whereas the z lifetime for LiSrPO4:Eu3+, B3+ with a mono exponential decay increased. The quantum efficiencies for LiSrPO4:Eu3+, B3+ phosphors varied between 89.83 %-96.78 % and exhibited approximately twice the efficiency of LiZnPO4:Eu3+, B3+. The usability of optimized LiMPO4:xEu3+, yB3+ (where M = Zn, Sr and x = 3 mol%, y = 100 mol%) phosphors was investigated for latent fingerprint applications.
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    A comparison of spectroscopic properties of Dy3+-doped tetragonal tungsten bronze MTa2O6 (M = Sr, Ba, Pb) phosphors based on Judd-Ofelt parameters
    Ilhan, M; Keskin, IÇ; Güleryüz, LF; Kati, MI
    TTB (tetragonal tungsten bronze) crystal structures exhibit very interesting physical properties as well as the superiority of having different cationic sites and allowing doping. In the study, the spectroscopic results of TTB-MTa2O6:Dy3+ (M = Sr, Ba, Pb) phosphors are presented using Judd-Ofelt (JO) intensity parameters. The PL and RL spectra of the phosphors exhibited the characteristic emissions of Dy in the visible and infrared regions. The PL excitation spectra were used to determine JO parameters (omega(2), omega(4), omega(6)). The decreasing trend of omega(2) parameter and PL asymmetry is SrTa2O6:Dy3+ > PbTa2O6:Dy3+ > BaTa2O6:Dy3+, which shows low electronegativity and shifting to the long wavelength of BaTa2O6:Dy3+ supports the low value of the omega(2) parameter and covalence. The PL decay profiles of all the phosphors are double exponential and the fast decreasing of PL decay components of SrTa2O6:Dy3+ is compatible with the concentration quenching after 5 mol%. The decreasing trend of the observed lifetime is in order BaTa2O6:Dy3+ > PbTa2O6:Dy3+ > SrTa2O6:Dy3+, which can be attributed to the defect centers depending on the increase of the covalency.
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    Evaluation of structural and spectroscopic results of tetragonal tungsten bronze MTa2O6 :Eu3+ (M = Sr, Ba, Pb) phosphors and comparison on the basis of Judd-Ofelt parameters
    Ilhan, M; Kati, MI; Keskin, IÇ; Güleryüz, LF
    The crystal structure with different cationic sites and the superiority of allowing doping make TTB (tetragonal tungsten bronze) structures very interesting in terms of exhibiting different physical properties. The new spectroscopic and structural results of MTa2O6:Eu3+ (M = Sr, Ba, Pb) phosphors were presented in the study. The incorporation of europium activator into the different cationic (Sr, Ba, Pb) tunnel structures of TTB crystal with TaO6 octahedral exhibited interesting structural and optical properties. The relationship between coordination number and CTB showed that the highly coordinated A and B sites of TTB crystal caused the CTB to shift to low energy or over 300 nm. The spectral properties of TTB-MTa2O6 :Eu3+ (M = Sr, Ba, Pb) phosphors were compared by determining the Judd-Ofelt (JO) intensity parameters from PL emission spectrum. The (decreasing trend of the Omega(2) parameter and asymmetry ratio is SrTa2O6:Eu3+ > BaTa2O6:Eu3+ > PbTa2O6:Eu3+, and the Eu-O bonds of PbTa2O6:Eu3+ compared to other matrices indicated a more ionic character and a relatively high symmetry environment around Eu3+. The deviation of the experimental (beta(exp)) and Judd-Ofelt (beta(cal)) branching ratios for transition D-5(0)-> F-7(2) are well below 10%, indicating good consistency. All the D-5(0) decay profiles of the phosphors are exponential, and slightly reductions occurred in the luminescence lifetimes for SrTa2O6:Eu3+ and BaTa2O6:Eu3+. XRD results of Eu3+ doped SrTa2O6 series of the high-temperature TTB polymorph reported in this study confirmed the single-phase up to 10 mol%. SEM examinations revealed the change of size and shape of SrTa2O6 samples depending on Eu3+ concentration. (C) 2022 Elsevier B.V. All rights reserved.