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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 Defect Characterization of Ga4se3< Layered Single Crystals by Thermoluminescence(indian Acad Sciences, 2016) Isik, M.; Delice, S.; Gasanly, N.Trapping centres in undoped Ga4Se3S single crystals grown by Bridgman method were characterized for the first time by thermoluminescence (TL) measurements carried out in the low-temperature range of 15-300 K. After illuminating the sample with blue light (similar to 470 nm) at 15 K, TL glow curve exhibited one peak around 74 K when measured with a heating rate of 0.4 K/s. The results of the various analysis methods were in good agreement about the presence of one trapping centre with an activation energy of 27 meV. Analysis of curve fitting method indicated that mixed order of kinetics dominates the trapping process. Heating rate dependence and distribution of the traps associated with the observed TL peak were also studied. The shift of peak maximum temperature from 74 to 113 K with increasing rate from 0.4 to 1.2 K/s was revealed. Distribution of traps was investigated using an experimental technique based on cleaning the centres giving emission at lower temperatures. Activation energies of the levels were observed to be increasing from 27 to 40 meV by rising the stopping temperature from 15 to 36 K.Article Citation - WoS: 6Citation - Scopus: 6Low-Temperature Thermo Luminescence Studies on Tlins2 Layered Single Crystals(Polish Acad Sciences inst Physics, 2014) Isik, M.; Delice, S.; Gasanly, N. M.Thermoluminescence characteristics of TlInS2 layered single crystals grown by the Bridgman method were investigated in the low temperature range of 10-300 K. The illuminated sample with blue light (approximate to 470 nm) at 10 K was heated at constant heating rate. Curve fitting, initial rise and various heating rate methods were used to determine the activation energy of the trap levels. All applied methods showed good consistency about the presence of five trapping centers located at 14, 19, 350, 420, and 520 meV. Behavior of the TL curve for various heating rates was investigated. Traps distribution has also been studied. The activation energies of the distributed trapping centers were found to be increasing from 14 to 46 meV.Article Citation - WoS: 14Citation - Scopus: 14Low Temperature Thermoluminescence Behaviour of Y2o3< Nanoparticles(Elsevier, 2019) Delice, S.; Isik, M.; Gasanly, N. M.Y2O3 nanoparticles were investigated using low temperature thermoluminescence (TL) experiments. TL glow curve recorded at constant heating rate of 0.4 K/s exhibits seven peaks around 19, 62, 91, 115, 162, 196 and 215 K. Activation energies and characteristics of traps responsible for observed curves were revealed under the light of results of initial rise analyses and T-max-T-stop experimental methods. Analyses of TL curves obtained at different stopping temperatures resulted in presence of one quasi-continuously distributed trap with activation energies increasing from 18 to 24 meV and six single trapping centers at 49, 117, 315, 409, 651 and 740 meV. Activation energies of all revealed centers were reported in the present paper. Structural characterization of Y2O3 nanoparticles was accomplished using X-ray diffraction and scanning electron microscopy measurements. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.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: 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: 4Citation - Scopus: 4Thermally Controlled Band Gap Tuning in Cuo Nano Thin Films for Optoelectronic Applications(indian Assoc Cultivation Science, 2024) Delice, S.; Isik, M.; Gasanly, N. M.Temperature dependency of band gap in CuO nano thin films has been investigated by virtue of transmission experiments at different temperatures. Structural and morphological characterization were achieved using X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. Analysis on the XRD diffractogram revealed the presence of monoclinic structure for the CuO. Average crystallite size was determined as 17.8 nm. Absorption characteristics in between 10 and 300 K were presented in the wavelength range of 360-1100 nm. The band gap of the CuO was found to be similar to 2.17 eV at 300 K using Tauc and spectral derivative methods. This value increased to similar to 2.24 eV at 10 K. Both methods showed that the band gap extended with decreasing temperature. Temperature dependency of the band gap was studied using Varshni relation. The band gap at absolute temperature, variation of the band gap with temperature and Debye temperature were calculated as 2.242 +/- 0.002 eV, - 5.4 +/- 0.2 x 10(-4) eV/K and 394 +/- 95 K, respectively.Article Low Temperature Thermoluminescence of Quaternary Thallium Sulfide Tl4inga3<(indian Assoc Cultivation Science, 2015) Delice, S.; Isik, M.; Bulur, E.; Gasanly, N. M.Thermoluminescence measurements have been carried out on Tl4InGa3S8 single crystals in the temperature range of 10-300 K at various heating rates. The observed thermoluminescence spectra have been analyzed applying many methods like curve fitting, initial rise, peak shape and heating rate methods. Thermal cleaning method has been performed on the observed thermoluminescence glow curve to separate the overlapped peaks. Three distinctive trapping centers with activation energies of 13, 44 and 208 meV have been revealed from the results of the analysis. Heating rate dependence and traps distribution investigations have been also undertaken on the most intensive peak. The thermoluminescence mechanisms in the observed traps have been attributed to first order kinetics (slow retrapping) on the strength of the consistency between theoretical assumptions for slow retrapping process and experimental outcomes.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: 2Citation - Scopus: 2Trap Distribution in Agin5s8< Single Crystals: Thermoluminescence Study(Pergamon-elsevier Science Ltd, 2018) Delice, S.; Işık, Mehmet; Isik, M.; Gasanly, N. M.; Işık, Mehmet; Department of Electrical & Electronics Engineering; Department of Electrical & Electronics EngineeringDistribution of shallow trap levels in AgIn5S8 crystals has been investigated by thermoluminescence (TL) measurements performed below room temperature (10-300 K). One broad TL peak centered at 33 K was observed as constant heating rate of 0.2 K/s was employed for measurement. The peak shape analysis showed that the TL curve could consist of several individual overlapping TL peaks or existence of quasi-continuous distributed traps. Therefore, TL experiments were repeated for different stopping temperatures (T-stop) between 10 and 34 K with constant heating rate of 0.2 K/s to separate the overlapping TL peaks. The E-t vs T-stop indicated that crystal has quasi-continuously distributed traps having activation energies increasing from 13 to 41 meV. Heating rate effect on trapped charge carriers was also investigated by carrying out the TL. experiments with various heating rates between 0.2 and 0.6 K/s for better comprehension of characteristics of existed trap levels. Analyses indicated that the trap levels exhibited the properties of anomalous heating rate behavior which means the TL intensity and area under the TL peak increase with increasing heating rate.
