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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 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 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.
