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Article Citation - WoS: 23Citation - Scopus: 25Investigation of Optical Properties of Bi12geo20< Sillenite Crystals by Spectroscopic Ellipsometry and Raman Spectroscopy(Elsevier Sci Ltd, 2020) Isik, M.; Delice, S.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Bi12GeO20 (BGO) compound is one of the fascinating members of sillenites group due to its outstanding photorefractive and photocatalytic characteristics. The present paper aims at investigating optical properties of BGO crystals by means of spectroscopic ellipsometry and Raman spectroscopy measurements. Bi12GeO20 single crystals grown by Czochralski method were structurally characterized by X-ray diffraction (XRD) experiments and the analyses showed that studied crystals have cubic crystalline structure. Raman spectrum exhibited 15 peaks associated with A, E and F modes. Spectroscopic ellipsometry measurement data achieved in the energy region between 1.2 and 6.2 eV were used in the air/sample optical model to get knowledge about complex pseudodielectric constant, pseudorefractive index, pseudoextinction and absorption coefficients of the crystals. Spectral change of real and imaginary part of complex pseudodielectric constant were discussed in detail. Band gap energy of Bi12GeO20 single crystals was calculated to be 3.18 eV using absorption coefficient dependency on photon energy. Critical point energies at which photons are strongly absorbed were determined by utilizing the second energy derivative spectra of components of complex pseudodielectric function. Fitting of both spectra resulted in the presence of four interband transitions with energies of 3.49, 4.11, 4.67 and 5.51 eV.Article Citation - WoS: 19Citation - Scopus: 20Optical characteristics of Bi12SiO20 single crystals by spectroscopic ellipsometry(Elsevier Sci Ltd, 2020) Isik, M.; Delice, S.; Nasser, H.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Structural and optical characteristics of Bi12SiO20 single crystal grown by the Czochralski method were investigated by virtue of X-ray diffraction (XRD) and spectroscopic ellipsometry measurements. XRD analysis indicated that the studied crystal possesses cubic structure with lattice parameters of a = 1.0107 nm. Spectral dependencies of several optical parameters like complex dielectric constant, refractive index, extinction and absorption coefficients were determined using ellipsometry experiments performed in the energy region of 1.2-6.2 eV. The energy band gap of Bi12SiO20 crystals was found to be 3.25 eV by utilizing absorption coefficient analysis. Moreover, critical point energies were calculated as 3.54, 4.02, 4.82 and 5.58 eV from analyses of the second energy derivative spectra of the complex dielectric constant.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.Article Citation - WoS: 7Citation - Scopus: 6Investigation of Optical Characteristics of Pbmoo4 Single Crystals by Spectroscopic Ellipsometry(Elsevier Gmbh, 2022) Delice, S.; Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.In this study, we investigated the optical properties of PbMoO4 single crystals grown by Czochralski method. Spectroscopic ellipsometry measurements were carried out in the energy region between 1.0 and 5.5 eV at room temperature. X-ray diffraction measurements were achieved for structural characterization. The resulted pattern exhibited one peak belonging to (200) plane. Spectral variations of complex dielectric function, complex refractive index, absorption coefficient and dissipation function were obtained from the analyses of ellipsometry data. Real part of dielectric function increased up to 4.0 eV and then decreased suddenly at above this value. Zero frequency refractive index and dielectric constant were found to be 2.04 and 4.15, respectively. High frequency dielectric constant was determined to be 4.36. Optical band gap of PbMoO4 crystals was calculated as 3.09 eV. Two critical points with energies of 3.57 and 4.34 eV were estimated from the analyses of second-energy derivative spectra of real and imaginary parts of dielectric function. It was determined that [MoO4]2- complexes and charge transfer from Pb2+ ions into the neighboring Mo groups were responsible for these interband transitions. Dissipation function increased with increasing photon energy.
