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Article Citation - WoS: 5Citation - Scopus: 5Growth and Temperature Tuned Band Gap Characteristics of Nabi(moo4)2< Single Crystal(Iop Publishing Ltd, 2023) Isik, M.; Guler, I; Gasanly, N. M.Structural and optical properties of double sodium-bismuth molybdate NaBi(MoO4)(2) semiconductor compound was investigated by x-ray diffraction, Raman and transmission experiments. From the x-ray diffraction experiments, the crystal that has tetragonal structure was obtained. Vibrational modes of the crystal were found from the Raman experiments. Transmission experiments were performed in the temperature range of 10-300 K. Derivative spectroscopy analysis and absorption spectrum analysis were performed to get information about the change in band gap energy of the crystal with temperature. It was observed that the band gap energies of the crystal at different temperatures obtained from these techniques are well consisted with each other. By the help of absorption spectrum which was obtained from transmission measurements performed at varying temperatures, absolute zero value of the band gap and average phonon energy as 3.03 +/- 0.02 eV and Eph = 24 +/- 0.2 meV, respectively. Moreover, based on absorption spectrum analysis the Urbach energy of the crystal was obtained as 0.10 eV.Article Citation - WoS: 10Citation - Scopus: 10Energy Band Gap and Oscillator Parameters of Ga4se3< Single Crystals(Pergamon-elsevier Science Ltd, 2007) Qasrawi, A. F.; Gasanly, N. M.The optical properties of the Bridgman method grown Ga4Se3S crystals have been investigated by means of room temperature, transmittance and reflectance spectral analysis. The optical data have revealed an indirect allowed transition band gap of 2.08 eV. The room temperature refractive index, which was calculated from the reflectance and transmittance data, allowed the identification of the dispersion and oscillator energies, static dielectric constant and static refractive index as 21.08 and 3.85 eV, 6.48 and 2.55, respectively. (C) 2007 Elsevier Ltd. All rights reserved.Article Citation - WoS: 4Citation - Scopus: 4Crystal Data and Indirect Optical Transitions in Tl2ingase4< Crystals(Pergamon-elsevier Science Ltd, 2008) Qasrawi, A. F.; Gasanly, N. M.The room temperature crystal data and the optical properties of the Bridgman method grown Tl2InGaSe4 crystals are reported and discussed. The X-ray diffraction technique has revealed that Tl2InGaSe4 is a single phase crystal of monoclinic structure. The unit cell lattice parameters, which were recalculated from the X-ray data, are found to be a = 0.77244 nm, b = 0.64945 nm, c = 0.92205 nm and beta = 95.03 degrees. The temperature dependence of the optical band gap of Tl2InGaSe4 single crystal in the temperature region of 290-500 K has also been investigated. The absorption coefficient was calculated from the transmittance and reflectance data in the incident photon energy range of 1.60-2.10 eV. The absorption edge is observed to shift toward lower energy values as temperature increases. The fundamental absorption edge corresponds to indirect allowed transition energy gap of 1.86 eV that exhibited a temperature coefficient gamma = -3.53 x 10(-4) eV/K. (C) 2007 Elsevier Ltd. All rights reserved.Article Citation - WoS: 14Citation - Scopus: 15Structural and Optical Properties of Ga2se3< Crystals by Spectroscopic Ellipsometry(Springer, 2019) Guler, I.; Isik, M.; Gasanly, N. M.; Gasanova, L. G.; Babayeva, R. F.Optical and crystalline structure properties of Ga2Se3 crystals were analyzed utilizing ellipsometry and x-ray diffraction (XRD) experiments, respectively. Components of the complex dielectric function (epsilon=epsilon(1)+i epsilon(2)) and refractive index (N=n+ik) of Ga2Se3 crystals were spectrally plotted from ellipsometric measurements conducted from 1.2eV to 6.2eV at 300K. From the analyses of second-energy derivatives of epsilon(1) and epsilon(2), interband transition energies (critical points) were determined. Absorption coefficient-photon energy dependency allowed us to achieve a band gap energy of 2.02eV. Wemple and DiDomenico single effective oscillator and Spitzer-Fan models were accomplished and various optical parameters of the crystal were reported in the present work.Article Citation - WoS: 5Citation - Scopus: 5Optical Properties of Tlgaxin1-x< Mixed Crystals (0.5 ≤ x ≤ 1) by Spectroscopic Ellipsometry, Transmission, and Reflection(Taylor & Francis Ltd, 2014) Isik, M.; Delice, S.; Gasanly, N. M.The layered semiconducting TlGaxIn1-xSe2-mixed crystals (0.5 <= x <= 1) were studied for the first time by spectroscopic ellipsometry measurements in the 1.2-6.2 eV spectral range at room temperature. The spectral dependence of the components of the complex dielectric function, refractive index, and extinction coefficient were revealed using an optical model. The interband transition energies in the studied samples were found from the analysis of the second-energy derivative spectra of the complex dielectric function. The effect of the isomorphic cation substitution (indium for gallium) on critical point energies in TlGaxIn1-xSe2 crystals was established. Moreover, the absorption edge of TlGaxIn1-xSe2 crystals have been studied through the transmission and reflection measurements in the wavelength range of 500-1100 nm. The analysis of absorption data revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps decrease with the increase of indium content in the studied crystals.Article Citation - WoS: 7Citation - Scopus: 8Optical Properties of Tl2ingas4< Layered Single Crystal(Elsevier Science Bv, 2007) Qasrawi, A. F.; Gasanly, N. M.The temperature dependence of the optical band gap of Tl2InGaS4 single crystal in the temperature region of 300-500 K and the room temperature refractive index, n(lambda), have been investigated. The absorption coefficient, which was calculated from the transmittance and reflectance spectra in the incident photon energy range of 2.28-2.48 eV, increased with increasing temperature. Consistently, the absorption edge shifts to lower energy values as temperature increases. The fundamental absorption edge corresponds to an indirect allowed transitions energy gap (2.35 eV) that exhibits a temperature coefficient of -4.03 x 10(-4) eV/K. The room temperature n(lambda), calculated from the reflectance and transmittance data, allowed the identification of the oscillator strength and energy, static and lattice dielectric constants, and static refractive index as 16.78 eV and 3.38 eV, 5.96 and 11.77, and 2.43, respectively. (c) 2006 Elsevier B.V. All rights reserved.Article Citation - WoS: 9Citation - Scopus: 9Determination of optical parameters of Ga0.75In0.25Se layered crystals(Wiley-v C H verlag Gmbh, 2012) Isik, M.; Gasanly, N. M.The optical properties of the Ga0.75In0.25Se crystals have been investigated by means of transmission and reflection measurements in the wavelength range of 380-1100 nm. The analysis of the results performed at room temperature revealed the presence of optical indirect transtions with band gap energy of 1.89 eV. The variation of the band gap energy as a function of temperature was also studied in the temperature range of 10-300 K. The rate of change of band gap energy (? = 6.2 x 10(4) eV/K) and absolute zero value of the band gap (Egi(0) = 2.01 eV) were reported. The wavelength dependence of the refractive index was analyzed using Wemple and DiDomenico, Sellmeier and Cauchy models to find the oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index values. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Article Citation - WoS: 4Citation - Scopus: 4Growth and Characterization of Nabi(mo0.5w0.5< Single Crystal: a Promising Material for Optoelectronic Applications(Elsevier Sci Ltd, 2023) Isik, M.; Guler, I.; Gasanly, N. M.The structural and optical characteristics of NaBi(Mo0.5W0.5O4)2 single crystals grown by Czochralski method were investigated. X-ray diffraction (XRD) pattern exhibited four well-defined peaks related to tetragonal crystalline structure with a space group I41/a. Raman and infrared transmittance spectra were recorded to investigate vibrational properties of the compound. Room temperature transmission spectrum was measured to reveal band gap energy of the crystal. The derivative spectral and absorption coefficient analyses resulted in direct band gap energy of 3.19 and 3.18 eV, respectively. Urbach energy of the crystal was also determined as 0.17 eV from photon energy dependency of absorption coefficient. The structural and optical parameters ob-tained for NaBi(Mo0.5W0.5O4)2 were compared with the parameters of the NaBi(XO4)2 (X: Mo,W) compounds to understand the effect of the composition on the studied properties. The reported characteristics of NaBi (Mo0.5W0.5O4)2 point out that the compound has significant potential to be used in optoelectronic devices.Article Citation - WoS: 16Citation - Scopus: 15Effect of Temperature on Band Gap of Pbwo4 Single Crystals Grown by Czochralski Method(Iop Publishing Ltd, 2022) Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.The structural and optical properties of PbWO4 single crystals grown by Czochralski method and investigated by x-ray diffraction (XRD) and transmission experiments. XRD pattern presented well-defined and intensive peaks related with tetragonal scheelite structure. Transmission experiments were accomplished for the first time at various temperatures between 10 and 300 K on PbWO4 single crystals to reveal variation of band gap with temperature. Derivative spectroscopy method presented the experimentally observed band gap energy as increasing from 3.20 to 3.35 eV when the temperature was decreased to 10 K from room temperature. The revealed energy was associated with transition taking place between delocalized and trap levels. Temperature-band gap energy plot was analyzed by Varshni and Bose-Einstein models. The fitting processes under the light of these models revealed optical characteristics of absolute zero experimentally observed band gap, variation rate of gap energy with temperature and Debye temperature of PbWO4 single crystal.Article Citation - WoS: 14Citation - Scopus: 14Temperature-Dependent Optical Properties of Gase Layered Single Crystals(Taylor & Francis Ltd, 2016) Isik, M.; Tugay, E.; Gasanly, N. M.Optical properties of GaSe single crystals have been investigated using temperature-dependent transmission and room temperature reflection measurements in the wavelength range of 380-1100nm. The analysis of the absorption data at room temperature showed the existence of indirect transitions in the crystal with energy band gap of 1.98eV. Temperature dependence of the transmission measurements revealed the shift of the absorption edge toward lower energy as temperature is increased from 10 to 280K. The rate of change of the indirect band gap was found as =-6.6x10(-4)eV/K from the analysis of experimental data under the light of theoretical relation giving the band gap energy as a function of temperature. The absolute zero value of the band gap energy and Debye temperature were calculated from the same analysis. The Wemple-DiDomenico single-effective-oscillator model applied to refractive index dispersion data was used to determine the oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index values.
