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Article Citation - WoS: 4Citation - Scopus: 4Optical Characterization of (tlins2)0.5< Crystal by Ellipsometry: Linear and Optical Constants for Optoelectronic Devices(Springer, 2023) Guler, I.; Isik, M.; Gasanly, N.TlInSSe [(TlInS2)(0.5)(TlInSe2)(0.5)] crystals have garnered significant attention as promising candidates for optoelectronic applications due to their exceptional optoelectrical characteristics. This study focused on investigating the linear and nonlinear optical properties of TlInSSe layered single crystals through ellipsometry measurements. The X-ray diffraction analysis revealed the presence of four distinct peaks corresponding to a monoclinic crystalline structure. In-depth analysis was conducted to examine the variations of refractive index, extinction coefficient, and complex dielectric function within the energy range of 1.25-6.15 eV. By employing derivative analysis of the absorption coefficient and utilizing the Tauc relation, the indirect and direct bandgap energies of TlInSSe crystals were determined to be 2.09 and 2.26 eV, respectively. Furthermore, this research paper presents findings on oscillator energy, dispersion energy, Urbach energy, zero and high frequency dielectric constants, plasma frequency, carrier density to effective mass ratio, nonlinear refractive index, and first-order and third-order nonlinear susceptibilities of TlInSSe crystals.Article Citation - WoS: 8Citation - Scopus: 8Spectroscopic ellipsometry study of Bi12TiO20 single crystals(Springer, 2021) Isik, M.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Bi12XO20 (X: Si, Ge, Ti, etc.) ternary compounds have attracted attention especially due to their fascinating photorefractive characteristics. The present paper introduces the structural and optical characteristics of Bi12TiO20 single crystals grown by Czochralski method. X-ray diffraction pattern of the compound exhibited sharp and intensive peaks corresponding to parallel planes of cubic crystalline structure. The lattice constant of the cubic structure was determined as a = 1.0118 nm using a diffraction pattern indexing program. The optical characterization of the Bi12TiO20 single crystals was carried through spectroscopic ellipsometry experiments performed in the 1.2-5.0 eV spectral range. The spectral dependencies of refractive index, extinction coefficient, and complex dielectric function were revealed analyzing experimental ellipsometric data under the light of sample-air optical model. The band gap energy of the compound was determined as 3.34 eV from the analyses of absorption coefficient. Three critical points at 3.51, 4.10, and 4.71 eV were obtained from the analyses of components of dielectric function using their second-energy derivative spectra.Article Citation - WoS: 14Citation - Scopus: 18Traps distribution in sol-gel synthesized ZnO nanoparticles(Elsevier, 2019) Delice, S.; Isik, M.; Gasanly, N. M.The distribution of shallow traps within the sol-gel synthesized ZnO nanoparticles was investigated using thermoluminescence (TL) experiments in the 10-300 K temperature range. TL measurements presented two overlapped peaks around 110 and 155 K. The experimental technique based on radiating the nanoparticles at different temperatures (T-exc.) between 60 and 125 K was carried out to understand the trap distribution characteristics of peaks. It was observed that peak maximum temperature shifted to higher values and activation energy (E-t) increased as irradiating temperature was increased. The E-t vs. T-exc. presented that ZnO nanoparticles have quasi-continuously distributed traps possessing activation energies increasing from 80 to 171 meV. (C) 2019 Elsevier B.V. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Optical Characterization of Nabi(moo4)2< Crystal by Spectroscopic Ellipsometry(Springer Heidelberg, 2024) Guler, I.; Isik, M.; Gasanly, N. M.The compound NaBi(MoO4)(2) has garnered significant interest in optoelectronic fields. This study employs spectroscopic ellipsometry to thoroughly examine the linear and nonlinear optical characteristics of NaBi(MoO4)(2) crystals, offering detailed insights into their optical behavior. Our investigation presents a precise method for discerning the crystal's spectral features, revealing the spectral variations of key optical parameters such as refractive index, extinction coefficient, dielectric function, and absorption coefficient within the 1.2-5.0 eV range. Through analysis, we determined optical attributes including bandgap energy, critical point energy, and single oscillator parameters. Additionally, we explored the nonlinear optical properties of NaBi(MoO4)(2), unveiling potential applications such as optoelectronic devices, frequency conversion, and optical sensors. This study enhances comprehension of optical properties of NaBi(MoO4)(2), underscoring its significance in future optical and electronic advancements.Article Citation - WoS: 3Citation - Scopus: 4Analysis of Temperature-Dependent Transmittance Spectra of Zn0.5in0.5< (zis) Thin Films(Springer, 2019) Isik, M.; Gullu, H. H.; Delice, S.; Gasanly, N. M.; Parlak, M.Temperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550-950nm and in temperature range of 10-300K. Transmission spectra shifted towards higher wavelengths (lower energies) with increasing temperature. Transmission data were analyzed using Tauc relation and derivative spectroscopy. Analysis with Tauc relation was resulted in three different energy levels for the room temperature band gap values of material as 1.594, 1.735 and 1.830eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814eV and one minima around 1.741eV. The determined energies from both methods were in good agreement with each other. The presence of three band gap energy levels were associated to valence band splitting due to crystal-field and spin-orbit splitting. Temperature dependence of the band gap energies were also analyzed using Varshni relation and gap energy value at absolute zero and the rate of change of gap energy with temperature were determined.Article Citation - WoS: 4Citation - Scopus: 5Thermoluminescence Properties of Tl2ga2< Layered Single Crystals(Amer inst Physics, 2013) Delice, S.; Isik, M.; Bulur, E.; Gasanly, N. M.The trap center(s) in Tl2Ga2S3Se single crystals has been investigated from thermoluminescence (TL) measurements in the temperature range of 10-300 K. Curve fitting, initial rise, and peak shape methods were applied to observed TL glow curve to evaluate the activation energy, capture cross section, and attempt-to-escape frequency of the trap center. One trapping center has been revealed with activation energy of 16 meV. Moreover, the characteristics of trap distribution have been studied using an experimental technique based on different illumination temperature. An increase of activation energy from 16 to 58 meV was revealed for the applied illumination temperature range of 10-25K. (C) 2013 AIP Publishing LLC.Article Citation - WoS: 10Citation - Scopus: 11Structural and Temperature-Tuned Bandgap Characteristics of Thermally Evaporated β-in2< Thin Films(Springer, 2021) Surucu, O.; Isik, M.; Terlemezoglu, M.; Gasanly, N. M.; Parlak, M.In2S3 is one of the attractive compounds taking remarkable interest in optoelectronic device applications. The present study reports the structural and optical characteristics of thermally evaporated beta-In2S3 thin films. The crystalline structure of the thin films was found as cubic taking into account the observed diffraction peaks in the X-ray diffraction pattern. The atomic compositional ratio of constituent elements was obtained as consistent with chemical formula of In2S3. Three peaks around 275, 309 and 369 cm(-1) were observed in the Raman spectrum. Temperature-tuned bandgap energy characteristics of the In2S3 thin films were revealed from the investigation of transmittance spectra obtained at various temperatures between 10 and 300 K. The analyses of the transmittance spectra indicated that direct bandgap energy of the In2S3 thin films decreases from 2.40 eV (at 10 K) to 2.37 eV (at 300 K) with the increase of measurement temperature. The bandgap energy vs. temperature relation was investigated by means of Varshni optical model. The fitting of the experimental data under the light of theoretical expression revealed the absolute zero bandgap energy, the rate of change of bandgap energy and Debye temperature.Article Citation - WoS: 6Citation - Scopus: 7Characteristic Features of Thermoluminescence in Neodymium-Doped Gallium Sulfide(Wiley, 2018) Guler, I.; Isik, M.; Ahmedova, F.; Guseinov, A.; Gasanly, N.The thermoluminescence (TL) of neodymium-doped gallium sulfide (GaS:Nd) single crystals was measured from 10 K to room temperature with various heating rates between 0.2 and 1.0 K/sec. Two peaks centered at 70.9 K and 116.0 K were observed when using a heating rate of 0.8 K/sec. Initial rise and curve fitting methods were used to obtain information on trap activation energies. Activation energies of 94 and 216 meV were found for two analyzable peaks. The heating rate dependencies of TL intensities revealed that one of the observed peaks showed normal behavior according to the one trap-one recombination model, whereas the other model showed anomalous heating rate behavior. TL experiments were also carried out at different illumination temperatures from 10 to 32 K; maximum peak temperature remained almost the same at various illumination temperatures. This behavior indicated that the revealed trapping centers are single, discrete levels. The TL glow curves of undoped GaS crystals were also investigated and the effect of Nd doping on the TL characteristics of crystals is discussed in the manuscript.Article Citation - WoS: 19Citation - Scopus: 19Temperature-Dependent Band Gap Characteristics of Bi12sio20< Single Crystals(Amer inst Physics, 2019) Isik, M.; Delice, S.; Gasanly, N. M.; Darvishov, N. H.; Bagiev, V. E.Bi12SiO20 single crystals have attracted interest due to their remarkable photorefractive characteristics. Since bandgap and refractive index are related theoretically to each other, it takes much attention to investigate temperature dependency of bandgap energy to understand the behavior of photorefractive crystals. The present study aims at investigating structural and optical characteristics of photorefractive Bi12SiO20 single crystals grown by the Czochralski method. The structural characterization methods indicated that atomic composition ratios of constituent elements were well-matched with the chemical compound Bi12SiO20, and grown crystals have a cubic crystalline structure. Optical properties of crystals were investigated by room temperature Raman spectroscopy and temperature-dependent transmission measurements between 10 and 300 K. The analyses of transmittance spectra by absorption coefficient and derivative spectrophotometry techniques resulted in energy bandgaps decreasing from 2.61 to 2.48 eV and 2.64 to 2.53 eV as temperature was increased from 10 to 300 K. The Varshni model was applied to analyze temperature-bandgap energy dependency.Article Citation - WoS: 5Citation - Scopus: 5Revealing Defect Centers in Pbwo4 Single Crystals Using Thermally Stimulated Current Measurements(Aip Publishing, 2024) Isik, M.; Gasanly, N. M.The trap centers have a significant impact on the electronic properties of lead tungstate (PbWO4), suggesting their crucial role in optoelectronic applications. In the present study, we investigated and revealed the presence of shallow trap centers in PbWO4 crystals through the utilization of the thermally stimulated current (TSC) method. TSC experiments were performed in the 10-280 K range by applying a constant heating rate. The TSC spectrum showed the presence of a total of four peaks, two of which were overlapped. As a result of analyzing the TSC spectrum using the curve fit method, the activation energies of revealed centers were found as 0.03, 0.11, 0.16, and 0.35 eV. The trapping centers were associated with hole centers according to the comparison of TSC peak intensities recorded by illuminating the opposite polarity contacts. Our findings not only contribute to the fundamental understanding of the charge transport mechanisms in PbWO4 crystals but also hold great promise for enhancing their optoelectronic device performance. The identification and characterization of these shallow trap centers provide valuable insights for optimizing the design and fabrication of future optoelectronic devices based on PbWO4.
