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Article Citation - WoS: 10Citation - Scopus: 9Structural and temperature-tuned band gap energy characteristics of PbMoO4 single crystals(Elsevier, 2022) Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.PbMoO4 is one of the member of the molybdate materials and has been a significant research interest due to its photocatalytic and optoelectronic applications. In the present paper, the structural and optical properties of PbMoO4 single crystals grown by Czochralski technique were investigated. X-ray diffraction pattern presented well-defined and intensive peaks associated with tetragonal scheelite structure. Energy dispersive spectroscopy analyses presented the atomic compositional ratio of constituent elements as consistent with chemical formula of PbMoO4. Raman and infrared transmittance spectra were reported to give information about the vibrational characteristics of the compound. Room temperature transmission spectrum was analyzed by derivative spectroscopy technique and band gap energy was found as 3.07 eV. Temperature-tuned band gap energy characteristics of the single crystal were investigated by performing transmission measurements at different temperatures between 10 and 300 K. The analyses indicated that band gap energy of the PbMoO4 single crystal increases to 3.24 eV when the temperature was decreased to 10 K. Temperature-band gap energy dependency was studied considering Varshni and Bose-Einstein models. The successful fitting processes under the light of applied models presented various optical parameters like absolute zero band gap energy, variation rate of band gap with temperature and Debye temperature.Article Citation - WoS: 11Citation - Scopus: 11Structural and Temperature-Tuned Optical Characteristics of Bi12geo20< Sillenite Crystals(Elsevier, 2020) Delice, S.; Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Sillenite compounds exhibit unique photorefractive and electro-optic characteristics providing attractiveness to these materials in various optoelectronic applications. The present paper aims at investigating one of the members of this family. Structural and optical characteristics of Bi12GeO20 (BGO) were studied by means of x-ray diffraction, Raman spectroscopy and temperature-dependent transmittance measurements. Obtained transmission curves in the wavelength range of 350-1100 nm and at different applied temperatures between 10 and 300 K were employed to find out the absorption coefficient dependence on the photon energy. Tauc relation revealed the presence of an energy gap of 2.49 eV at room temperature. Extension of energy gap up to 2.57 eV due to decreased temperature down to 10 K was deduced by the analysis. In order to have reliable results, the energy gap value was corroborated by utilizing derivative spectral method and well consistency between both methods was indicated. Energy gap change with temperature was also discussed in the study using an empirical formula developed by Varshni. Energy gap at absolute zero and rate of band gap alteration with temperature were determined as 2.57 eV and -2.4 x 10(-4) eV K (- 1), respectively. Taking into account the previously reported studies on investigation of band gap characteristics of BGO, intrinsic Bi-Ge(3+) + V-O(+) defect could be responsible for the revealed energy value of 2.49 eV which is much lower than reported band gap energy of similar to 3.2 eV.Article Citation - WoS: 4Citation - Scopus: 4Trapping Centers in Bi12tio20< Single Crystals by Thermally Stimulated Current(Elsevier, 2021) Isik, M.; Delice, S.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Sillenite group compounds have been widely utilized in photocatalytic applications. One of the member of this group, Bi12TiO20 single crystal, was grown by Czochralski method. The structural properties were investigated by x-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. XRD pattern presented well-defined intensive peaks associated with cubic crystalline structure. SEM images indicated the crystal surface as almost uniform and smooth. Thermally stimulated current (TSC) experiments were performed in the 10-280 K temperature range to reveal shallow trapping centers in the Bi12TiO20 single crystal. Two peaks around 112 and 179 K were observed in the TSC glow curve. The analyses of these curves considering the curve fitting and peak shape techniques resulted in presence of two hole centers at 0.09 and 0.14 eV. Heating rate dependencies of peak maximum temperature and current were also investigated throughout the paper.Article Citation - WoS: 7Citation - Scopus: 6Spectroscopic Ellipsometry Characterization of Pbwo4 Single Crystals(Elsevier, 2022) Delice, S.; Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Optical characterization of PbWO4 single crystals grown by Czochralski method was achieved in virtue of spectroscopic ellipsometry experiments carried out in the energy region of 1.0-5.6 eV at room temperature. Tetragonal scheelite structure with lattice parameters of a = b = 5.4619 & Aring; and c = 12.0490 & Aring; was determined for the bulk crystal utilizing from XRD analysis. Analyses of the ellipsometry data presented the photon energy dependencies of complex dielectric function of the crystal. The real part of the dielectric function exhibited increasing behavior with energy in the below 4.1 eV and then decreased immediately. Zero frequency refractive index and dielectric constant were determined to be 2.02 and 4.08, respectively, using Wemple and DiDomenico oscillator model. High frequency dielectric constant was calculated as 4.30 by Spitzer-Fan model. Optical band gap of PbWO4 was found to be 3.24 eV from the dielectric relaxation time spectrum. Moreover, existence of two critical points with energies of 3.70 and 4.58 eV was revealed from the analyses of extinction coefficient and second derivative of the dielectric function. These levels were considered to be due to creation of cation exciton (Pb2+ 6s(2) - Pb2+ 6s6p) and transitions in the [WO4](2-) group.
