Search

Bi12MO20 (M: Si, Ge, Ti, etc.) compounds are known as sillenites having fascinating photorefractive characteristics. The present paper reports the structural and optical characteristics of one of the members of this family, Bi12TiO20 single crystals, grown by Czochralski method. X-ray diffraction pattern of the crystal presented sharp and intensive peaks associated with planes of cubic crystalline structure with lattice constant of a = 1.0142 nm. The optical properties were studied by means of room temperature Raman and temperature-dependent transmission experiments at various temperatures between 10 and 300 K. Raman spectrum indicated peaks around 127, 162, 191, 219, 261, 289, 321, 497 and 537 cm(-1). The analyses of transmittance spectra indicated the increase of direct bandgap energy from 2.30 to 2.56 eV as temperature was decreased from room temperature to 10 K. The temperature-dependent bandgap characteristics of Bi12TiO20 were analyzed by means of Varshni and O'Donnell-Chen models. The analyses under the light of these models resulted in absolute zero bandgap energy of E-g(0) = 2.56(4) eV, rate of change of bandgap energy of gamma = - 1.11 x 10(-3) eV/K and average phonon energy of < E-ph & rang; = 8.6 meV. WOS:000592613600005 2-s2.0-85096598213

Cu0.5Ag0.5InSe2 (CAIS) thin films were deposited on a glass substrate by sequential sputtering of Cu, Ag, and In2Se3-stacked film layers. Structural characterization showed that the deposited CAIS film satisfies nearly the stoichiometric form with uniform and homogeneous surface structure. The single-phase polycrystalline behavior without any secondary-phase formation was observed from the diffraction profile. The optical properties were investigated using temperature-dependent transmission measurements in the wavelength region of 600-1100 nm and in between 10 and 300 K. In the region of interest, the transmission spectra shifted towards the higher wavelengths as a result of an increase in the sample temperature. The analysis of the absorption data based on the transmission spectra resulted in absorption coefficient values of around 10(5) cm(-1) and the presence of direct allowed optical transition. From the Tauc plots, CAIS samples were found to have three distinct direct optical transitions depending on the possible splitting in the valence band. The obtained room temperature uppermost band gap energy value of 1.09 eV was found in the energy limit of ternary analogues (CuInSe2 and AgInSe2), and also in a good agreement with the previous works in the literature. The dependency of the band gap energy on the temperature was analyzed using fundamental relations. In addition, the electrical characteristics of the film layer were discussed in four-contact conductivity measurements, and room temperature conductivity was observed as 0.8 ohm(-1) cm(-1). Additionally, two activation energy values were found in the temperature-dependent conductivity profile. As a diode application, CAIS/Si heterojunction was fabricated and the main diode parameters were extracted at dark and room temperature conditions. WOS:000514350200061 2-s2.0-85076374052

Bi12GeO20 single crystal grown by Czochralski method was investigated in terms of thermoluminescence (TL) properties. TL experiments were performed for various heating rates between 1 and 6 K/s in the temperature region of 300-675 K. One TL peak with peak maximum temperature of 557 K was observed in the TL spectrum as constant heating rate of 1 K/s was employed. Curve fitting, initial rise and variable heating rate methods were applied to calculate the activation energy of trap level corresponding to this TL peak. Analyses resulted in a presence of one trap center having mean activation energy of 0.78 eV. Heating rate characteristics of revealed trap center was also explored and theoretically well-known behavior that TL intensity decreases and peak maximum temperature increases with heating rates was observed for the trap level. Distribution of trapping levels was studied by thermally cleaning process for different T-stop between 425 and 525 K. Quasi-continuously distributed trapping levels were revealed with mean activation energies ranging from 0.78 to 1.26 eV. Moreover, absorption analysis revealed an optical transition taking place between a defect level and conduction band with an energy difference of 2.51 eV. These results are in good agreement for the presence of intrinsic defects above valence band in Bi12GeO20 crystals. ATILIM UniversityAtilim University [ATU-ADP-1920-03] This work was supported by ATILIM University under Grant No: ATU-ADP-1920-03. WOS:000629775100026 2-s2.0-85099335771

Thermally stimulated current (TSC) investigations of p-GaS (gallium sulfide) single crystals grown by Bridgman method were achieved by virtue of consecutive experiments carried out at various heating rates in between 0.4 and 1.0 K/s in the temperature range of 10-280 K. One single TSC peak around 148 K and overlapped, incomplete peaks in the end limit temperature of the experiments were observed in the spectrum recorded at constant heating rate of 1.0 K/s. Individual peak was analyzed utilizing curve fitting method. Existence of one trapping level centered at 0.11 eV was revealed by the analyses. Heating rate dependency of obtained TSC curve was also studied and it was shown that TSC intensity decreased besides increase of peak maximum temperature with heating rate. Characteristics feature of trapping mechanism was investigated in detail by employing different stopping temperature between 50 and 110 K. Analyses on T-m-T-stop dependency resulted in a presence of quasi-continuously distributed traps with activation energies ranging from 0.11 to 0.55 eV. The revealed trap was thought to be arising from intrinsic defect possibly created by V-Ga or antisite S-Ga. WOS:000618875200003 2-s2.0-85098226341

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 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 Earths Orta DoÄŸu Teknik Ãœniversitesi: GAP-105-2018-2752 This work was supported by the Middle East Technical University (METU) , Project No: GAP-105-2018-2752 . 2-s2.0-85055083731

Analyses 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.

Trapping 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 GmbH

Sillenite group compounds have been widely utilized in photocatalytic applications. One of the member of this group, Bi12TiO20 single crystal, was grown by Czochralski method. The structural properties were investigated by x-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. XRD pattern presented well-defined intensive peaks associated with cubic crystalline structure. SEM images indicated the crystal surface as almost uniform and smooth. Thermally stimulated current (TSC) experiments were performed in the 10–280 K temperature range to reveal shallow trapping centers in the Bi12TiO20 single crystal. Two peaks around 112 and 179 K were observed in the TSC glow curve. The analyses of these curves considering the curve fitting and peak shape techniques resulted in presence of two hole centers at 0.09 and 0.14 eV. Heating rate dependencies of peak maximum temperature and current were also investigated throughout the paper.

Transmission 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 Ltd

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. © 2020 Elsevier Ltd and Techna Group S.r.l. Atilim Üniversitesi: ATÜ-ADP-1920-03 This work was supported by Atilim University under Grant No: ATÜ-ADP-1920-03 . 2-s2.0-85079182234

Sillenite compounds exhibit unique photorefractive and electro-optic characteristics providing attractiveness to these materials in various optoelectronic applications. The present paper aims at investigating one of the members of this family. Structural and optical characteristics of Bi12GeO20 (BGO) were studied by means of x-ray diffraction, Raman spectroscopy and temperature-dependent transmittance measurements. Obtained transmission curves in the wavelength range of 350-1100 nm and at different applied temperatures between 10 and 300 K were employed to find out the absorption coefficient dependence on the photon energy. Tauc relation revealed the presence of an energy gap of 2.49 eV at room temperature. Extension of energy gap up to 2.57 eV due to decreased temperature down to 10 K was deduced by the analysis. In order to have reliable results, the energy gap value was corroborated by utilizing derivative spectral method and well consistency between both methods was indicated. Energy gap change with temperature was also discussed in the study using an empirical formula developed by Varshni. Energy gap at absolute zero and rate of band gap alteration with temperature were determined as 2.57 eV and -2.4 x 10(-4) eV K (- 1), respectively. Taking into account the previously reported studies on investigation of band gap characteristics of BGO, intrinsic Bi-Ge(3+) + V-O(+) defect could be responsible for the revealed energy value of 2.49 eV which is much lower than reported band gap energy of similar to 3.2 eV. ATILIM UniversityAtilim University [ATU-ADP-1920-03] This work was supported by ATILIM University under Grant No: ATU-ADP-1920-03. WOS:000559138200007 2-s2.0-85086868023

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. Atilim UniversityAtilim University [ATUADP-1920-03] This work was supported by Atilim University under Grant No: ATUADP-1920-03. WOS:000571889900005 2-s2.0-85088630853

Structural and optical properties of SnS2xSe(2-2x) thin films grown by magnetron sputtering method were investigated for composition of x = 0.5 (SnSSe) in the present study. X-ray diffraction, energy dispersive X-ray spectroscopy, atomic force microscopy and scanning electron microscopy methods were used for structural characterization while temperature-dependent transmission measurements carried out at various temperatures in between 10 and 300 K were accomplished for optical investigations. X-ray diffraction pattern of studied composition presented peaks at positions which are between those of SnSe2 and SnS2. Transmittance spectra recorded at all applied temperatures were analyzed using well-known Tauc relation. Analyses revealed the direct band gap energy value of SnSSe thin films as 1.75 eV at room temperature. Change of band gap energy as a response to varying temperature were discussed in the study by utilizing Varshni relation. It was shown that variation of gap energy values was well-matched with the Varshni's empirical formula. Energy band gap at absolute zero and rate of change of band gap with temperature were found to be 1.783 eV and -2.1 x 10(-4) eV K-1, respectively. WOS:000535462600016 2-s2.0-85082121091

Temperature-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. 2-s2.0-85065029400

Temperature-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 Ltd 2-s2.0-85062893878

In 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 Ltd 2-s2.0-85059446122

Thermoluminescence (TL) 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. Tmax − Texc. analysis was accomplished for TL peaks at relatively higher temperature region to reveal the related traps depths. Tmax − Texc. 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. Keywords: Lanthanide oxides, Gd2O3, Thermoluminescence, Defects

The 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. Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, TÜBITAK: 116F304 This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK), Project No: 116F304 2-s2.0-85062208913

The 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.

Characterization of shallow trapping centers in GaS0.5Se0.5 crystals grown by a Bridgman method was carried out in the present work using thermoluminescence (TL) measurements performed in the low temperature range of 10–300 K. The activation energies of the trapping centers were obtained under the light of results of various analysis methods. The presence of three trapping centers located at 6, 30 and 72 meV was revealed. The analysis of the experimental glow curve gave reasonable results under the model that assumes slow retrapping which states the order of kinetics as b=1. Heating rate dependence of the observed TL peaks was studied for the rates between 0.4 and 1.0 K/s. Distribution of the traps was also investigated using an experimental technique based on the thermal cleaning of centers giving emission at lower temperatures. The distributed levels with activation energies increasing from 6 to 136 meV were revealed by increasing the stopping temperature from 10 to 52 K.

Trapping centres in undoped Ga 4Se 3S 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 (∼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.

Optical and thermoluminescence properties on GaS0.75Se0.25 crystals were investigated in the present work. Transmission and reflection measurements were performed at room temperature in the wavelength range of 400–1000 nm. Analysis revealed the presence of indirect and direct transitions with band gap energies of 2.39 and 2.53 eV, respectively. TL spectra obtained at low temperatures (10–300 K) exhibited one peak having maximum temperature of 168 K. Observed peak was analyzed using curve fitting, initial rise and peak shape methods to calculate the activation energy of the associated trap center. All applied methods were consistent with the value of 495 meV. Attempt-to-escape-frequency and capture cross section of the trap center were determined using the results of curve fitting. Heating rate dependence studies of the glow curve in the range of 0.4–0.8 K/s resulted with decrease of TL intensity and shift of the peak maximum temperature to higher values.

Praseodymium (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 Ltd

Distribution of shallow trap levels in AgIn 5 S 8 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.

Trap centres in gallium sulfide single crystals have been investigated by thermoluminescence measurements in the temperature range of 10–230 K. A curve-fitting method was utilized to evaluate the activation energies (52, 200 and 304 meV) of the revealed three trap centres. The heating rate dependence and trap distribution of the peaks have been studied using experimental techniques based on various heating rates and various illumination temperatures, respectively. An anomalous heating rate dependence of the high-temperature peak was found by carrying out TL measurements with various heating rates between 0.2 and 1.0 K/s. This behaviour was explained on the basis of a semi-localized transition model. Whereas normal heating rate dependence was established for low-temperature peak, that is, the TL intensity of the glow curve decreases and the peak maximum temperature shifts to higher values with increasing the heating rate. Moreover, a quasi-continuous trap distribution with the increase of activation energi...

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 (≈ 470 nm) at 10 K was heated at constant heating rate. Curve tting, 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 ve 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.

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.

Defect characterization of Tl2Ga2Se3S single crystals has been performed by thermoluminescence (TL) measurements at low temperatures between 10 and 70 K with various heating rate ranging from 0.6 to 1.0 K/s. The TL signal due to the luminescence from trap centers revealed one glow peak having maximum temperature of 36 K. Curve fitting and various heating rate methods were used for the analysis of the glow curve. The activation energy of 13 meV was found by the application of curve fitting method. This practical method also established that the trap center exhibits the characteristics of mixed (general) kinetic order. In addition, various heating rate analysis gave a compatible result (13 meV) with curve fitting as the temperature lag effect was taken into consideration. Distribution of traps was also investigated using an experimental method. A quasi-continuous distribution was attributed to the determined trap centers.

Trap centers in Tl2GaInS4 single crystals have been investigated by thermoluminescence (TL) measurements in the temperature range of 10–110 K. Curve-fitting method was utilized to evaluate the activation energies (12 and 26 meV) of revealed two trap centers. Thermal cleaning method was applied to the spectra and two overlapping peaks were reduced to one single peak corresponding to deeper trap level. The characteristics of heating rate dependence and trap distribution of the separated peak have been studied using experimental techniques based on various heating rates and various illumination temperatures, respectively. Anomalous heating rate dependence was observed carrying out TL measurements with various heating rate between 0.2 and 1.2 K s−1. This behavior was explained on the base of a semi-localized transition model. Moreover, increase of activation energy from 27 to 67 meV was revealed for the applied illumination temperature range of 26–36 K.

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 t...

Thermoluminescence (TL) measurements were performed on Tl4Ga3InSe8 layered single crystals grown by Bridgman method in the temperature range of 10–200 K. After illuminating the sample with blue light at 10 K and heating at a rate of 1.0 K s−1 in dark, TL curve exhibited peaks around 46 and 123 K. Thermal activation energies of the trap levels corresponding to the observed peaks were determined using curve fitting, initial rise and peak shape methods. Analyses have revealed the presence of two defect centers with activation energies of 7 and 41 meV. The consistency between the theoretical predictions for slow retrapping and experimental results showed that the retrapping process for the observed centers was negligible. Measurements at different heating rates and illumination temperatures were also carried out for the high-temperature peak. Distribution of traps has been established as a result of experiments. An increase of activation energy from 45 to 147 meV was revealed with the change of illumination temperature from 40 to 80 K.

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.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 e...

Thermoluminescence (TL) measurements in Tl2InGaSe4-layered single crystals have been carried out in the temperature range of 10–200 K at various heating rates (0.2–1.0 K s−1) to get information about the characteristics of traps. Two TL overlapping glow peaks related to defect levels have been clearly observed. Thermal cleaning procedure was applied to the glow curves to separate overlapped peaks. Initial rise, peak shape, and heating rate methods were used to calculate the activation energies of the revealed traps. The energy values of 5 and 28 meV were evaluated for the peaks observed at low and high temperatures, respectively. Moreover, heating rate dependence and traps distribution analysis were also investigated on the curve obtained after thermal cleaning. The activation energies of the distributed trapping centers were found to be increasing from 29 to 151 meV with increasing the illumination temperature from 42 to 80 K.

The properties of trapping centres in – as grown – Tl4GaIn3S8 layered single crystals were investigated in the temperature range of 10–300 K 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 ~12 to ~125 meV by increasing the illumination temperature from 10 to 36 K. The analysis revealed that the first-order kinetics (slow retrapping) obeys for deeper level located at 292 meV.

In 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 GmbH

Characteristics 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.

The defect centers in TlGaSSe single crystals have been investigated by performing thermoluminescence (TL) measurements with various heating rates between 0.5 K/s and 1.0 K/s in the temperature range of 10–180 K. The TL spectra, with peak maximum temperatures at 39 K and 131 K, revealed the existences of two defect levels. Curve fitting, initial rise and peak shape methods were used to determine the activation energies of two defect centers. The experimental results also showed that the trapping process was dominated by second-order kinetics for the trap related with low temperature peak while the general order (mixed order) kinetics was dominant for the trap donated to high temperature peak. Furthermore, heating rate dependences and traps distributions were studied for two defect centers separately. Thermal quenching effect dominates the behavior of these defects as the heating rate is increased. Also, quasi-continuous distributions were established with the increase of the activation energies from 16 meV to 27 meV and from 97 meV to 146 meV for the traps associated with the peaks observed at low and high temperatures, respectively.

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 10–25 K.