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Article Citation - WoS: 8Citation - Scopus: 8Thermoluminescence Properties of Zno Nanoparticles in the Temperature Range 10-300 K(Springer, 2016) Isik, M.; Yildirim, T.; Gasanly, N. M.Low-temperature thermoluminescence (TL) properties of ZnO nanoparticles grown by sol-gel method were investigated in the 10-300 K temperature range. TL glow curve obtained at 0.2 K/s constant heating rate exhibited one broad peak around 83 K. The observed peak was analyzed using curve fitting method to determine the activation energies of trapping center(s) responsible for glow curve. Analyses resulted in the presence of three peaks at 55, 85 and 118 K temperatures with activation energies of 12, 30 and 45 meV, respectively. Thermal cleaning process was applied to separate overlapped peaks and get an opportunity to increase the reliability of results obtained from curve fitting method. Heating rate dependence of glow curve was also studied for rates between 0.2 and 0.7 K/s. The shift of the peak maximum temperatures to higher values and decrease in peak height with heating rate were observed. Moreover, X-ray diffraction and scanning electron microscopy were used for structural characterization.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: 2Citation - Scopus: 2Investigation of Defect Levels in Bi12sio20< Single Crystals by Thermally Stimulated Current Measurements(Iop Publishing Ltd, 2021) Isik, M.; Delice, S.; Gasanly, N. M.Bi12SiO20 (BSO) single crystal belongs to the sillenite semiconducting family known as defective compounds. The present paper investigates the defect centers in BSO grown by Czochralski method by means of thermally stimulated current (TSC) measurements performed in the 10-260 K range. The TSC glow curve obtained at heating rate of beta = 0.1 K s(-1) presented several peaks associated with intrinsic defect centers. The activation energies of defect centers were revealed as 0.09, 0.15, 0.18, 0.22, 0.34, 0.70 and 0.82 eV accomplishing the curve fit analyses method. The peak maximum temperatures and orders of kinetics of each deconvoluted peak were also determined as an outcome of fitting process. TSC experiments were expanded by making the measurements at various heating rates between 0.1 and 0.3 K s(-1) to get information about the heating rate dependent peak parameters.Article Citation - WoS: 17Citation - Scopus: 17Trap Distribution in Tlins2 Layered Crystals From Thermally Stimulated Current Measurements(Korean Physical Soc, 2008) Isik, M.; Goksen, K.; Gasanly, N. M.; Ozkan, H.We have carried out thermally stimulated current (TSC) measurements with the current flowing along the layer on as-grown TlInS2 layered single crystals in the low temperature range 10 - 110 K with different heating rates of 0.1 - 1.5 K/s. Experimental evidence was found for the presence of two shallow electron trapping centers with activation energies of 12 and 14 meV. Their capture cross sections have been determined as 2.2 x 10(-23) and 7.1 x 10(-25) cm(2), respectively. It was concluded that retrapping in these centers is negligible, which was confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumed slow retrapping. An exponential distribution of electron traps was revealed from the analysis of the TSC data obtained at different light excitation temperatures. This experimental technique provided a value of 27 meV/decade for the trap distribution. The parameters of the monoclinic unit cell were determined by studying the X-ray powder diffraction.Article Citation - WoS: 2Citation - Scopus: 2Thermoluminescence Characteristics of Tl4gain3< Layered Single Crystals(Taylor & Francis Ltd, 2014) Delice, S.; Isik, M.; Gasanly, N. M.The properties of trapping centres in - as grown - Tl4GaIn3S8 layered single crystals were investigated in the temperature range of 10-300K using thermoluminescence (TL) measurements. TL curve was analysed to characterize the defects responsible for the observed peaks. Thermal activation energies of the trapping centres were determined using various methods: curve fitting, initial rise and peak shape methods. The results indicated that the peak observed in the low-temperature region composed of many overlapped peaks corresponding to distributed trapping centres in the crystal structure. The apparent thermal energies of the distributed traps were observed to be shifted from similar to 12 to similar to 125meV by increasing the illumination temperature from 10 to 36K. The analysis revealed that the first-order kinetics (slow retrapping) obeys for deeper level located at 292meV.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: 2Citation - Scopus: 2Thermoluminescence Dose Response and Kinetic Parameters of Gd-Doped Zno Nanoparticles(Iop Publishing Ltd, 2024) Isik, M.; Yildirim, T.; Guner, M.; Gasanly, N. M.This study investigates the thermoluminescence (TL) properties of undoped and gadolinium (Gd)-doped zinc oxide (ZnO) nanoparticles synthesized via sol-gel method. The crystal structure of both synthesized nanoparticles was determined as hexagonal from x-ray diffraction pattern. The TL curve of undoped ZnO nanoparticles reveals two distinct peaks at 400.5 and 479.2 K, each associated with trap centers featuring activation energies of 0.84 and 1.05 eV. TL curve of the Gd:ZnO introduced three peaks associated with trap centers at 1.10, 1.18, and 1.25 eV. Notably, the absence of the 0.84 eV trap center in Gd-doped ZnO implies a modification in the defect structure. Considering the effect of Gd-doping on the band structure and potential minor errors in the analysis results, it was stated that the traps at 1.05 and 1.10 eV levels belonged to the same defect center. Dose-dependent investigations for undoped and Gd-doped ZnO nanoparticles reveal linear behaviors in the TL response, highlighting their potential for dosimetric applications. Photoluminescence spectra of both compounds exhibited emission peaks around 455 and 577 nm, which were associated with native defect centers.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: 8Citation - Scopus: 8Study of the Structural and Optical Properties of Thallium Gallium Disulfide (tlgas2) Thin Films Grown Via Thermal Evaporation(Iop Publishing Ltd, 2022) Isik, M.; Karatay, A.; Ech-Chergui, A. N.; Gasanly, N. M.Thallium gallium disulfide (TlGaS2) belonging to layered structured semiconducting family has been a significant compound due to its outstanding characteristics. Its layered characteristics take attention for two-dimensional (2D) material research area and thus TlGaS2 is known as promising layered compound to develop 2D materials for optoelectronic devices. To the best of our knowledge, the present work is the first one investigating TlGaS2 thin films grown by thermal evaporation method. The current study focused into the structural, morphological, and optical characteristics of thermally evaporated TlGaS2 thin films. X-ray diffraction pattern of the films exhibited one peak around 36.10 degrees which was associated with (-422) plane of the monoclinic crystalline structure. The atomic compositional ratio of Tl:Ga:S was found to be suitable for the chemical formula of TlGaS2. Scanning electron microscopy images showed uniformly and narrowly deposited nanoparticles with sizes varying between 100 and 200 nm. Room temperature transmission measurements were recorded to obtain the bandgap energy of the evaporated thin films. Tauc analyses indicated direct band gap energy of 2.60 eV. Finally, Urbach energy was obtained as 95 meV. The results of the present paper would provide valuable insight to 2D material technology to understand the potential device applications of the TlGaS2.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.
