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Article Citation - WoS: 10Citation - Scopus: 11Low Temperature Thermoluminescence of Gd2o3< Nanoparticles Using Various Heating Rate and tmax< - texc< Methods(Elsevier, 2019) Delice, Serdar; Isik, Mehmet; Gasanly, Nizami M.Thermoluminescence (FL) measurements for Gd2O3 nanoparticles were carried out for various heating rates between 0.3 and 0.8 K/s at low temperatures (10-280 K). TL spectrum exhibited two observable and one faint peaks in the temperature region of 10-100 K, and four peaks in the temperature region of 160-280 K. Heating rate analysis was achieved to understand the behaviors of trap levels. It was seen that the peak maximum temperatures and TL intensities of all peaks increase with increasing heating rate. This behavior was ascribed to anomalous heating rate effect. T-max - T(exc )analysis was accomplished for TL, peaks at relatively higher temperature region to reveal the related traps depths. T-max - T-exc plot presented a staircase structure indicating that the TL glow curve is composed of well separated glow peaks. Mean activation energies of trapping centers corresponding to these separated peaks were found as 0.43, 0.50, 0.58 and 0.80 eV.Article Citation - WoS: 10Citation - Scopus: 10Ellipsometry Study of Optical Parameters of Agin5s8< Crystals(Elsevier, 2015) Isik, Mehmet; Gasanly, NizamiAgln(5)S(8) crystals grown by Bridgman method were characterized for optical properties by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficient were obtained from ellipsometiy experiments carried out in the 1.2-6.2 eV range. Direct band gap energy of 1.84 eV was found from the analysis of absorption coefficient vs. photon energy. The oscillator energy, dispersion energy and zero-frequency refractive index, high-frequency dielectric constant values were found from the analysis of the experimental data using Wemple-DiDomenico and Spitzer-Fan models. Crystal structure and atomic composition ratio of the constituent elements in the AgIn5S8 crystal were revealed from structural characterization techniques of X-ray diffraction and energy dispersive spectroscopy. (C) 2015 Elsevier B.V. All rights reservedArticle Citation - WoS: 28Citation - Scopus: 28Structural, Morphological and Temperature-Tuned Bandgap Characteristics of Cus Nano-Flake Thin Films(Elsevier, 2022) Isik, Mehmet; Terlemezoglu, Makbule; Gasanly, Nizami; Parlak, MehmetCopper sulfide (CuS) thin films were produced by radio-frequency (RF) magnetron sputtering method. Structural, morphological and optical characteristics of deposited CuS films were presented. X-ray diffraction pattern showed two intensive peaks associated with hexagonal crystalline structure. Scanning electron microscopy image indicated that CuS films have nano-flake structured. Raman spectrum was reported to show vibrational characteristics of the CuS nano-flake thin films. Two peaks associated with Cu-S and S-S vibrations were observed in the Raman spectrum. Transmission spectra were recorded at various temperatures between 10 and 300 K. The analyses accomplished considering Tauc expression demonstrated that direct bandgap energy decreases from 2.36 eV (at 10 K) to 2.22 eV (at 300 K). Temperature-bandgap dependency was analyzed considering Varshni and Bose-Einstein expressions to reveal bandgap at 0 K, rate of change of bandgap and Debye temperature. CuS nanoflake thin film may be used in optoelectronic and photocatalysis applications thanks to its direct and narrow bandgap energy characteristics.Article Citation - WoS: 9Citation - Scopus: 14Bifunctional Praseodymium-Doped Sns2 Thin Films for Photocatalytic and Antibacterial Applications(Elsevier, 2024) Ech-Chergui, Abdelkader Nebatti; Bennabi, Farid; Isik, Mehmet; Khane, Yasmina; Garcia, Francisco Jose Garcia; Kadari, Ali Sadek; Amrani, BouhalouaneThis paper introduces a novel application of bifunctional Pr-doped SnS2 thin films, demonstrating their efficacy in both photocatalytic degradation of dye and antibacterial activities. The thin films were fabricated using an eco-friendly spray-coated method, encompassing undoped and Pr-doped SnS2 variations. The study comprehensively examines the structural, morphological, chemical, photocatalytic, and antibacterial characteristics of these films. The crystal structure of both undoped and Pr-doped SnS2 thin films exhibited hexagonal patterns, prominently favouring the growth in (1 0 1) orientation. Notably, an increase in crystallite size was observed with higher levels of Pr-doping. Raman spectroscopy analysis highlighted a distinct peak at 315 cm -1, corresponding to the A1 g vibrational mode associated with Sn-S bonds along the c-axis of the structure. Employing X ray Photoelectron Spectroscopy (XPS), the presence of essential components - Sn, S, and Pr - within the fabricated thin films was confirmed, consistent with experimental values of undoped and Pr -doped SnS2-x compositions. Importantly, the XPS analysis confirmed the integration of the Pr3+ oxidation state within Pr -doped SnS2 films. The photocatalytic degradation and antibacterial activities of the films were investigated. Notably, the photocatalytic potential of the synthesized materials against Congo Red exhibited a direct correlation with the Pr3+ doping percentage, indicating enhanced pollutant degradation with increasing doping levels. Similarly, the antibacterial performance against Escherichia coli displayed improvement with increasing Pr -doping content, highlighting the promising antimicrobial capabilities of the films. This study presents an innovative avenue to address both organic pollutant degradation and microbial control. By harnessing the attributes of Pr -doped SnS2 thin films, this research introduces a promising strategy for sustainable material applications in environmental purification and improvement in public health.Article Citation - WoS: 45Citation - Scopus: 43Investigation of Structural, Electronic, Magnetic and Lattice Dynamical Properties for Xcobi (x: Ti, Zr, Hf) Half-Heusler Compounds(Elsevier, 2020) Surucu, Gokhan; Isik, Mehmet; Candan, Abdullah; Wang, Xiaotian; Gullu, Hasan HuseyinStructural, electronic, magnetic, mechanical and lattice dynamical properties of XCoBi (X: Ti, Zr, Hf) Half-Heusler compounds have been investigated according to density functional theory and generalized gradient approximation. Among alpha, beta and gamma structural phases, gamma-phase structure has been found as the most stability characteristics depending on the calculated formation enthalpies, energy-volume dependencies and Cauchy pressures. Energy-volume plots of possible magnetic orders of gamma-phase XCoBi compounds have been analyzed and the most stable order has been found as paramagnetic nature. The theoretical studies on gamma-phase structures resulted in band gap energies of 0.96, 0.99 and 0.98 eV for TiCoBi, ZrCoBi and HfCoBi semiconducting compounds, respectively. Born-Huang criteria applied on elastic constants of interest compounds has indicated that gamma-phase is also mechanically stable for all studied compounds. In addition, various mechanical, lattice dynamical and thermodynamical parameters of XCoBi compounds have been calculated in the present study.Article Citation - WoS: 21Citation - Scopus: 20Nonlinear Optical Absorption Characteristics of Pbmoo4 Single Crystal for Optical Limiter Applications(Elsevier, 2022) Pepe, Yasemin; Isik, Mehmet; Karatay, Ahmet; Gasanly, Nizami; Elmali, AyhanMolybdate materials take great interest due to their photocatalytic and optoelectronic applications. In this report, PbMoO4 single crystal, one of the member of molybdate materials, is grown by Czochralski technique and the change of nonlinear absorption characteristic depending on the input intensity was reported. Linear absorption analysis revealed the band gap energy and Urbach energy as to be 3.12 and 0.52 eV, respectively. Nonlinear absorption characteristics of the PbMoO4 single crystal was examined with the open aperture (OA) Z-scan experiments at 532 nm excitation wavelength under various input intensities. Fitting results of the OA Z-scan experiments indicated that PbMoO4 single crystal has nonlinear absorption (NA) behavior, and NA coefficient (beta(eff)) increased from 7.11 x 10(-8) to 1.96 x 10(-7) m/W with increasing input intensity. This observation was associated with the increase of the contribution of the free carrier absorption to the NA with the generation of more excited electrons with increasing input intensity. At the 532 nm excitation wavelength (2.32 eV), the dominant mechanisms were revealed as one photon and free carrier absorptions. The optical limiting threshold of the PbMoO4 single crystal was obtained to be 4.91 mJ/cm(2). The reported results indicated that PbMoO4 single crystal can be a good optical limiter in the visible wavelength region due to its effective NA behavior.Article Citation - WoS: 21Citation - Scopus: 21The Role of Defects on the Transition From Saturable Absorption To Nonlinear Absorption of Bi12geo20< Single Crystal Under Increasing Laser Excitation(Elsevier, 2022) Pepe, Yasemin; Isik, Mehmet; Karatay, Ahmet; Yildiz, Elif Akhuseyin; Gasanly, Nizami; Elmali, AyhanThis work reports defect and input intensity dependent nonlinear optical behaviors of Bi12GeO20 (BGO) single crystal. Open aperture (OA) Z-scan experiments were performed with 532 nm excitation wavelength under 4 ns and 100 fs pulsed laser irradiation. Obtained data were fitted with a theoretical model considering one-photon, two-photon and free carrier absorption contributions to nonlinear absorption due to longer lifetime of localized defect states than that of used laser pulse durations. At low input intensities, the BGO single crystal showed saturable absorption (SA) behavior and transition to nonlinear absorption (NA) behavior observed with further increase of the input intensities both of pulse durations. At low input intensity, the OPA mechanism is dominant and results in SA by filling of the defect states due to defect state at around one photon energy (2.32 eV). At higher input intensity, multi-photon, two-photon and free carrier absorption become dominant mechanisms, and nonlinear absorption behavior was observed. The lowest saturation threshold was found as 1.36 x 1010 W/cm2 with nanosecond pulses. We have revealed the mechanisms contributing both SA and NA, and determined saturation intensity threshold and effective nonlinear absorption coefficients. Our findings indicate that the tails of defect states overlap in the energy band gaps especially in sufficiently disordered crystal. With this way, the spectral range for saturable absorption and nonlinear absorption can be broadened.Article Citation - WoS: 22Citation - Scopus: 22Wavelength Dependence of the Nonlinear Absorption Performance and Optical Limiting in Bi12tio20 Single Crystal(Elsevier, 2023) Pepe, Yasemin; Isik, Mehmet; Karatay, Ahmet; Gasanly, Nizami; Elmali, AyhanIn this study, the influence of excitation wavelength and input intensity on the nonlinear absorption (NA) mechanism and optical limiting behavior of the Bi12TiO20 (BTO) single crystal were reported. The energy band gap of the BTO single crystal was obtained to be 2.38 eV. Urbach energy revealed that the single crystal has a highly defective structure. Open aperture (OA) Z-scan experiments were conducted at 532 and 1064 nm exci-tation wavelengths at various input intensities. Obtained experimental data were analyzed with a theoretical model considering one photon, two-photon and free carrier absorption contributions to NA. The obtained results revealed that the BTO single crystal possesses NA. The NA coefficient increased with increasing input intensity at 532 nm excitation wavelength, while it decreased with increasing input intensity at 1064 nm excitation wave-length. Due to the intense localized defect states distribution at the energy of 532 nm excitation wavelength within the band gap, increasing contribution to NA came from one photon absorption (OPA), sequential two -photon absorption (TPA) and free carrier absorption (FCA) with increasing input intensity. The filling of the defect states at 1064 excitation wavelength caused a reduction in NA due to increasing saturable absorption with increasing input intensity. TPA coefficients were also found from the fitting ignoring the defect states. As ex-pected, the values of the nonlinear absorption coefficient beta eff are higher than that of the TPA coefficients for both excitation wavelengths. The optical limiting threshold of the BTO single crystal was obtained to be 6.62 mJ/cm2. The results of the present works indicated that BTO single crystal can be used as a potential optical limiter.Article Citation - WoS: 12Citation - Scopus: 14Excitation Wavelength Dependent Nonlinear Absorption Mechanisms and Optical Limiting Properties of Bi12sio20 Single Crystal(Elsevier, 2023) Dogan, Anil; Karatay, Ahmet; Isik, Mehmet; Pepe, Yasemin; Gasanly, Nizami; Elmali, AyhanNonlinear absorption mechanisms (NA), excitation wavelength dependence, and defect states of Bi12SiO20 (BSO) single crystal were investigated. The band gap and Urbach energies were found to be 2.51 and 0.4 eV from the absorption spectra. To evaluate the effect of excitation energy on the NA mechanism of the BSO single crystal, open aperture Z-scan experiment with 4 ns laser pulse at 532 and 1064 nm wavelengths with different intensities was performed. Obtained data were analyzed with a theoretical model considering the contributions of one photon absorption (OPA), two photon absorption (TPA) and free carrier absorption (FCA) to NA. The results indicated that the NA behavior decreased with increasing of the pump intensity as the defect states at around 2.32 eV by OPA at 532 nm, and TPA at 1064 nm excitations. The dominant NA mechanisms are OPA and sequential TPA at 532 nm as compared to the 1064 nm. A higher NA coefficient was obtained at 532 nm as compared to 1064 nm excitation. This observation was attributed to higher contribution of OPA at 532 nm even at lower input intensities compared to TPA contribution at 1064 nm. Onset optical limiting thresholds were found as 0.34 and 0.68 mJ/cm2 for 532 and 1064 nm input beams, respectively. In the light of the results, the BSO single crystal may be used as a saturable absorber or an optical limiter at convenient input intensity by effectively adjusting defect states and excitation wavelength.Article Citation - WoS: 8Citation - Scopus: 8The Investigation of Electronic Nature and Mechanical Properties Under Spin Effects for New Half-Metallic Ferromagnetic Chalcogenides Ag3crx4< (x = S, Se, and Te)(Elsevier, 2021) Erkisi, Aytac; Yildiz, Bugra; Wang, Xiaotian; Isik, Mehmet; Ozcan, Yusuf; Surucu, GokhanThis study presents the electronic and mechanical characteristics of ternary silver-based Ag3CrX4 (X = S, Se, and Te) chalcogenides having simple cubic crystalline structure (SC), conforming P4-3m (space group: 215) that are studied under the spin-polarized Generalized Gradient Approach (GGA) within the framework of the Density Functional Theory (DFT). The stable magnetic phase has been determined as the ferromagnetic (FM) phase for all studied systems. Then, phase stability, mechanical, thermal and electronic characteristics of Ag3CrX4 chalcogenides have been reported. In the calculated spin polarized electronic band structures for Ag3CrX4 chalcogenides, as an indicator of half-metallic behavior, metallicity has been observed in the majority spin channel, while indirect band gaps (1.04 eV for Ag3CrS4, 1.10 eV for Ag3CrSe4, and 1.25 eV for Ag3CrTe4) have been determined in the minority spin channel. Moreover, Ag3CrX4 chalcogenides have been found as thermodynamically stable and structurally synthesizable considering the calculated negative formation enthalpies. Elastic constants of studied chalcogenides satisfying Born-Huang criteria's pointed out the mechanical stability of materials. The predicted mechanical properties determined with elastic constants revealed that Ag3CrX4 chalcogenides belong to soft and ductile material family.
