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Öğe Analysis of temperature-dependent transmittance spectra of Zn0.5In0.5Se (ZIS) thin films(Springer New York LLC, 2019) Işık, Mehmet; Güllü, Hasan Hüseyin; Delice, Serdar; Gasanly, Nizami Mamed; Parlak, MehmetTemperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550–950 nm and in temperature range of 10–300 K. 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 1.830 eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814 eV and one minima around 1.741 eV. 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. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Öğe Characterization of trap centers in Gd2O3 nanoparticles by low temperature thermoluminescence measurements(Elsevier GmbH, 2018) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami MamedTrapping centers in Gd2O3 nanoparticles were investigated using thermoluminescence (TL) measurements in the below room temperature region of 10–280 K. Seven peaks having peak maximum temperatures between 30 and 252 K were observed in the TL spectra measured at constant heating rate of 0.3 K/s. Activation energies, order of kinetics and frequency factors were reported using three different analysis techniques: curve fitting, initial rise and peak shape methods. Activation energies of the trapping centers were found between 0.012 eV and 0.79 eV. Most of the TL transitions associated with observed peaks were found as dominated by mixed order of kinetics. Structural characterization of used nanoparticles was achieved using x-ray diffraction and scanning electron microscopy experiments. © 2017 Elsevier GmbHÖğe Defect characterization in neodymium doped thallium indium disulfide crystals by thermoluminescence measurements(Elsevier B.V., 2016) Delice, Serdar; Gasanly, Nizami MamedCharacteristics of defect centers in neodymium doped TlInS2 single crystals have been investigated in virtue of thermoluminescence measurements carried out at low temperatures (10–300 K) with various heating rates between 0.4 and 1.2 K s?1. One glow peak was detected with peak maximum temperature of 26 K at a rate of 0.4 K s?1. The observed glow peak was analyzed using three points and heating rate methods. The analysis results revealed the presence of one trap level with activation energy of 14 meV. Three points method showed that mixed order of kinetic dominates the trapping level. Shift of peak maximum temperature to higher values and decrease in TL intensity were observed as the heating rate was increased progressively. Distribution of traps was demonstrated using an experimental method based on illumination temperature varying between 10 and 14 K. © 2016 Elsevier B.V.Öğe Dose dependence effect of thermoluminescence process in TlInS2:Nd single crystals(Elsevier GmbH, 2017) Kadari, Ahmet; Delice, Serdar; Gasanly, Nizami MamedIn this paper, thermoluminescence (TL) properties of TlInS2:Nd single crystals were modeled using an interactive model (one trap and one kind of recombination center). The simulated work presented here was based on the experiment conducted by Delice et al. The thermoluminescence glow curve of TlInS2:Nd single crystals has been characterized by one main peak at 26 K, which confirm the presence of one active electron trap level in the forbidden band of this material. The model used in this work is similar to other models cited previously in the literature. The calculated glow curve was in good agreement with the experimental one. Our numerical results show also that the thermoluminescence intensity increases with the increase of the dose rate (D). In the selected dose level range; the thermoluminescence response is linear and no saturation can be observed. © 2017 Elsevier GmbHÖğe Effect of heating rate on thermoluminescence characteristics of Y2O3 nanoparticles(Elsevier B.V., 2019) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami MamedThe present paper reports the results of heating rate dependencies of thermoluminescence (TL)peaks observed for Y 2 O 3 nanoparticles in the below room temperature region. TL glow curve presented six peaks around 62.5, 91.3, 114.5, 162.7, 196.0 and 214.9 K for heating rate of 0.4 K/s. The increase of heating rate resulted in increase in peak maximum temperature and decrease in peak maximum intensity as expected according to theoretical information. Peak maximum temperature-heating rate dependencies of observed peaks were analysed according to exponential dependency relation. Curve fit and initial rise methods were applied on thermally cleaned individual peaks and activation energies of associated trap centers, frequency factors and order of kinetics were obtained from the analyses. Activation energy values of the revealed trapping centers found from both methods were in good agreement with each other. Moreover, lattice parameters, crystalline size and micro-strain of nanoparticles were investigated by means of x-ray diffraction measurements. © 2019 Elsevier B.V.Öğe Effect of N doping on TL2GA2S3SE single crystals: thermoluminescence characterization of defect centers(Eskişehir Teknik Üniversitesi, 2018) Delice, SerdarThermoluminescence study on nitrogen doped Tl2Ga2S3Se single crystals was achieved by performing the experiments with different stopping temperatures of 10?24 K and various heating rates between 0.4 and 1.2 K/s below room temperature. Thermoluminescence peak with peak maximum temperature of 54 K was detected from the emitted luminescence. Two trap levels were obtained from the observed spectra. Curve fitting and initial rise methods were applied to compute the activation energies and the values of 34 ± 2 and 70 ± 4 meV were found. Thermal cleaning process was applied to separate the overlapping peaks and so true energy region of trapping levels was corroborated. Moreover, variations of shape and position of TL curve were studied by investigating the heating rate behavior of trap levels. The best known behavior which the peak maximum temperature increases while the thermoluminescenceÖğe Investigation of optical properties of Bi12GeO20 sillenite crystals by spectroscopic ellipsometry and Raman spectroscopy(Elsevier Ltd, 2020) Işık, Mehmet; Delice, Serdar; Gasanly, Nizami; Bagiev, Vidadi E.Bi12GeO20 (BGO) compound is one of the fascinating members of sillenites group due to its outstanding photorefractive and photocatalytic characteristics. The present paper aims at investigating optical properties of BGO crystals by means of spectroscopic ellipsometry and Raman spectroscopy measurements. Bi12GeO20 single crystals grown by Czochralski method were structurally characterized by X-ray diffraction (XRD) experiments and the analyses showed that studied crystals have cubic crystalline structure. Raman spectrum exhibited 15 peaks associated with A, E and F modes. Spectroscopic ellipsometry measurement data achieved in the energy region between 1.2 and 6.2 eV were used in the air/sample optical model to get knowledge about complex pseudodielectric constant, pseudorefractive index, pseudoextinction and absorption coefficients of the crystals. Spectral change of real and imaginary part of complex pseudodielectric constant were discussed in detail. Band gap energy of Bi12GeO20 single crystals was calculated to be 3.18 eV using absorption coefficient dependency on photon energy. Critical point energies at which photons are strongly absorbed were determined by utilizing the second energy derivative spectra of components of complex pseudodielectric function. Fitting of both spectra resulted in the presence of four interband transitions with energies of 3.49, 4.11, 4.67 and 5.51 eV.Öğe Low temperature thermoluminescence behaviour of Y2O3 nanoparticles(Chinese Society of Rare Earths, 2019) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami MamedY2O3 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 Tmax?Tstop 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. © 2018 Chinese Society of Rare EarthsÖğe Low temperature thermoluminescence of Gd2O3 nanoparticles using various heating rate and Tmax???Texc. methods(Elsevier B.V., 2019) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami MamedThermoluminescence (TL) measurements for Gd 2 O 3 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. © 2019Öğe Optical characteristics of Bi12SiO20 single crystals by spectroscopic ellipsometry(Elsevier, 2020) Işık, Mehmet; Delice, Serdar; Nasser, H.; Gasanly, Nizami Mamed; Darvishov, N. H.; Bagiev, V. E.Structural and optical characteristics of Bi12SiO20 single crystal grown by the Czochralski method were investigated by virtue of X-ray diffraction (XRD) and spectroscopic ellipsometry measurements. XRD analysis indicated that the studied crystal possesses cubic structure with lattice parameters of a = 1.0107 nm. Spectral dependencies of several optical parameters like complex dielectric constant, refractive index, extinction and absorption coefficients were determined using ellipsometry experiments performed in the energy region of 1.2-6.2 eV. The energy band gap of Bi12SiO20 crystals was found to be 3.25 eV by utilizing absorption coefficient analysis. Moreover, critical point energies were calculated as 3.54, 4.02, 4.82 and 5.58 eV from analyses of the second energy derivative spectra of the complex dielectric constant.Öğe Structural and temperature-dependent optical properties of thermally evaporated CdS thin films(Elsevier Ltd, 2019) Işık, Mehmet; Güllü, Hasan Hüseyin; Delice, Serdar; Parlak, Mehmet; Gasanly, Nizami MamedIn this work, structural and temperature dependent optical properties of thermally evaporated CdS thin films were investigated. X-ray diffraction, energy dispersive spectroscopy and Raman spectroscopy experiments were carried out to characterize the thin films and obtain information about the crystal structure, atomic composition, surface morphology and vibrational modes. Temperature-dependent transmission measurements were performed in between 10 and 300 K and in the spectral range of 400–1050 nm. The analyses of transmittance spectra were accomplished by two different methods called as the absorption coefficient and the derivative spectrophotometry analyses. All evaluated band gap energy values at each studied temperature were in good agreement with each other depending on the applied analyses techniques. Room temperature gap energy values were found around 2.39 eV and 2.40 eV from absorption coefficient and derivative spectrophotometry analyses, respectively. Band gap energy depending on the sample temperature was studied under the light of two different models to investigate average phonon energy, electron phonon coupling parameter and the rate of change of band gap energy with temperature. © 2019 Elsevier LtdÖğe Study of the optical and photoelectrical properties of TlGaSeS layered single crystals(Elsevier Ltd, 2017) Delice, Serdar; Gasanly, Nizami MamedTransmission spectra (T) of TlGaSeS crystals in the photon energy (h?) range 1.38–2.38 eV are used to determine the energy gap. The indirect band gap of 2.30 eV was established employing the photon energy dependence of the first derivative dT/d(h?) and the photon energy dependence of absorption coefficient. In order to obtain information about the defect states in the energy gap of TlGaSeS crystals, photoconductivity (PC) measurements are performed in the 140–300 K range. Photoconductivity spectra in the photon energy range of 1.77–3.10 eV show two peaks related to intrinsic and extrinsic excitations. It was revealed that the first peak shifts slightly towards the low energy side with increasing temperature, whereas the second one shifts more significantly to the high energy range. It was assumed that for latter peak the deviating PC originates from the distributed energy levels in the band gap where the photoelectrons arise or where they go. © 2017 Elsevier LtdÖğe Study on thermoluminescence of TlInS2 layered crystals doped with Pr(Elsevier Ltd, 2018) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami MamedPraseodymium (Pr) doped TlInS2 crystals were studied by means of thermoluminescence (TL) measurements performed below room temperature with various heating rates. Detected TL signal exhibited glow curve consisting in overlapping two TL peaks at temperatures of 35 K (peak A) and 48 K (peak B) for 0.6 K/s heating rate. TL curve was analyzed with curve fitting and initial rise methods. Both of the applied methods resulted in consistent activation energies of 19 and 45 meV. The revealed trap levels were found to be dominated by mixed order of kinetics. Various heating rate dependencies of TL glow curves were also investigated and it was found that while peak A shows usual behavior, peak B exhibits anomalous heating rate behavior. Distribution of trap levels was explored using an experimental method called as Tmax?Tstop method. Quasi-continuous distributions with increasing activation energies from 19 to 29 meV (peak A) and from 45 to 53 meV (peak B) were ascribed to trap levels. Effect of Pr doping on the TL response of undoped TlInS2 crystals was discussed in the paper. © 2018 Elsevier LtdÖğe Temperature dependence of band gaps in sputtered SnSe thin films(Elsevier Ltd, 2019) Delice, Serdar; Işık, Mehmet; Güllü, Hasan Hüseyin; Terlemezoğlu, Makbule; Bayraklı Sürücü, Özge; Parlak, Mehmet; Gasanly, Nizami MamedTemperature-dependent transmission experiments were performed for tin selenide (SnSe) thin films deposited by rf magnetron sputtering method in between 10 and 300 K and in the wavelength region of 400–1000 nm. Transmission spectra exhibited sharp decrease near the absorption edge around 900 nm. The transmittance spectra were analyzed using Tauc relation and first derivative spectroscopy techniques to get band gap energy of the SnSe thin films. Both of the applied methods resulted in existence of two band gaps with energies around 1.34 and 1.56 eV. The origin of these band gaps was investigated and it was assigned to the splitting of valence band into two bands due to spin-orbit interaction. Alteration of these band gap values due to varying sample temperature of the thin films were also explored in the study. It was seen that the gap energy values increased almost linearly with decreasing temperature as expected according to theoretical knowledge. © 2019 Elsevier LtdÖğe Temperature lag effect on TL glow peaks: Corrections on kinetic parameters(Elsevier B.V., 2018) Delice, SerdarAnalyses on TL glow curves recorded with various heating rates for some ternary and quaternary crystals were accomplished using peak maximum temperatures (Tmax) which are experimentally obtained and corrected according to temperature lag effect proposed by Kitis and Tuyn. Curve fitting, initial rise, peak shape and variable heating rate methods were applied to experimental and corrected TL peaks. In spite of the fact that heating rate does not affect activation energy of a TL peak, analyses performed on the experimentally obtained TL curves resulted in an increment of the activation energy with increasing heating rate. However, as the corrected TL data were used for the analyses, the activation energy values of each TL peak recorded with different heating rate were in good agreement with each other. The detailed analyses on studied samples were given in the present paper. © 2018 Elsevier B.V.Öğe Temperature-dependent band gap characteristics of Bi12SiO20 single crystals(American Institute of Physics Inc., 2019) Işık, Mehmet; Delice, Serdar; Gasanly, Nizami; Darvishov, Namiq H.; Bagiev, Vidadi 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.Öğe Trap distribution in AgIn5S8 single crystals: Thermoluminescence study(Elsevier Ltd, 2018) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami MamedDistribution 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 (Tstop) between 10 and 34 K with constant heating rate of 0.2 K/s to separate the overlapping TL peaks. The Et vs Tstop 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. © 2017 Elsevier LtdÖğe Traps distribution in sol-gel synthesized ZnO nanoparticles(Elsevier B.V., 2019) Delice, Serdar; Işık, Mehmet; Gasanly, Nizami MamedThe 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. © 2019 Elsevier B.V.
