Narrow Results

The activation energy E (eV) of the first-order thermoluminescence (TL) glow peak is currently obtained using a two heating rates method. However, this method having the common drawback, that it assumes the first-order kinetics in the luminescence process. In the present work, an equation is suggested to determine the activation energy E (eV) of any glow peak, independent on the kinetics order of the process. To apply this method, three heating rates (β₁,β₂,β₃), the corresponding peak temperatures (T₁,T₂,T₃) and intensities (I₁,I₂,I₃) of the isolated glow peaks are required. The applicability of the suggested method is demonstrated here by taking some numerically computed first-, second- and general-order TL glow peaks.

The prediction of fading for the glow peaks relevant to dosimetry of iodised salt has been made using the values of the trapping parameters, namely the thermal activation energy (E), frequency factor (s) and the order of kinetic (b). This theoretical prediction has been checked with experimentally observed glow curves recorded after storage period of 2, 5, 10, 165, 375 and 790 days at room temperature (~21°C). Excellent agreement has been observed between the experimental and theoretical glow curves. This has been possible because of reliable retrieval of the trapping parameters by the use of Computerised Glow Curve Deconvolution (CGCD) as well as state-of-art of data acquisition system. The concept developed in the present paper in principle may be applied to any TLD.

In order to elucidate the type of trap distribution in borate glass we have analyzed a set of glow peaks around 110°C recorded with different doses of β-ray irradiation. The glow curves are subjected to the rigorous Computerized Glow Curve Deconvolution (CGCD) both in the framework of kinetic formalism and differential equation formalism to judge which type of trap distribution favors in borate glass. It is observed that the distribution of traps is exponential, which is also well supported by standard error analyses i.e. Figure Of Merit (FOM) and Chi-square (χ²) test.

Photoluminescence (PL) and Thermoluminescence (TL) properties of Cerium (Ce³⁺) and Terbium (Tb³⁺) singly doped and multidoped monocalcium aluminate phosphors are studied. The suitability of monocalcium aluminate material as a luminescent host is analyzed. The nature of trap centers and the possibility of energy transfer between the dopant ions are discussed. The suitability of the material for radiation dosimetry application is also studied.

We discovered that Sr₂MgSi₂O₇:Eu phosphor emits blue light under the application of a mechanical stress, a phenomenon known as mechanoluminescence (ML). The ML showed a similar spectrum as photoluminescence (PL), which indicated that ML is emitted from the same center of Eu²⁺ ions as PL. The analysis of structure and thermoluminescne suggested that the origin of ML for Sr₂MgSi₂O₇:Eu phosphor can be attributed to strain-induced electroluminescence, that is, piezoelectricity impelled the trapped electrons to escape from the trap and produce ML. Furthermore, the relation between ML intensity and compressive load is close to linearity, which indicate that this sample can be used for smart-skin and self-diagnosis applications.

Nowadays, the pacific use of ionizing radiation has attracted a great deal of attention in medicine, as well as in radiodiagnostic, and radiotherapy. However to avoid unnecessary irradiations to the healthy tissue, a strict quality control is required. This has led to the development of a new dosimeter equivalent to the tissue that could be highly suitable for the radiation dosimetry. The borate of magnesium with its low effective atomic number (Z_eff), is considered equivalent to the human-tissue. For this reason, in this work, we present the results obtained of the thermoluminescent characterization of this material. The test that was carried out includes the lower detection limit, sensitivity, reproducibility of the TL measurement, stability of information (fading), and TL response as a function of the delivered dose and energy response, which are recommended by the International Commission on Radiological Units and Measurements (ICRU) and International Commission on Radiological Protection (ICRP). Two different concentrations of Dy activator were used i.e. 1.25 (batch A) and 1.5 (batch B) mol%. Meanwhile, the Na activator was 0.5 mol% in both cases. The results show that this new thermoluminescent material is adequate for radiation dosimetry in different medical applications.

In this work, we show the influence of heating rate (H.R.) on the thermoluminescence (TL) signal of BaSO₄ activated by Eu ions. The maximum temperature, the TL integral, the activation energy, the frequency factor and full width at half maximum of the TL glow-peak as a function of the H.R. were studied. The TL reading system used was a Harshaw TL reader model 4000, with constant H.R. in the range from 2 to 12 K/s. The irradiation dose was 0.1 Gy from ⁶⁰Co in all cases. The kinetic parameters and their dependence on the H.R. were evaluated using the sequential quadratic programming glow curve deconvolution (SQPGCD). The experimental results showed that as the H.R. increases, the I_M shifts to higher temperature; similar behavior of the kinetics parameters were obtained.

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.

In this paper, the simulation of the thermal cleaning procedure in LiF:Mg,Ti as well as the investigation of the origin of its glow-peaks have been performed by six electron trapping levels and one recombination center phenomenological model. The most generally accepted parameter of the glow-peaks 1 to 5 of LiF:Mg,Ti is their first-order kinetics; this was particularly investigated by the use of the random variation of the kinetic parameters method.

The catalyst surface was processed in the high-voltage electrical discharge device in oxygen environment. Continuous active oxide centers formed on the surface and complete filling of the surface with oxygen occur, and its thermo-physical properties, thermo-luminescence curves, scanning electron microscope and ESR spectrometers were studied. It was determined that the activity of the catalyst at values of the absorbed dose $D\le 21$kGy is many times higher than that of conventional catalysts. Thus, due to the sorption volume of the surface, the volume of the product formed in the liquid phase increases by 1.6 times.

In this paper, the co-precipitation method was used to synthesize pure and Ag-doped LiF crystals and the effect of crystalline cube sizes and Ag concentration on the thermoluminescent (TL) response is reported. The synthesized materials were characterized by scanning electron microscopy and their morphology and size distributions were determined. Crystal sizes were found to be strongly dependent on the ethanol:water ratio, varying from 4.1$\mu$m to 150nm for pure LiF crystals. For Ag-doped samples, the best ethanol:water ratio was found to be 9:1, giving crystals from 0.50$\mu$m to 1.21$\mu$m. A single cubic crystalline phase was determined by XRD for all synthesized samples. The photoluminescence spectra as well as UV-Vis absorbance were also analyzed. The TL response to X-ray irradiation was studied for an exposition of 43R. Two effects were observed in the TL response. The first concerns with a significant dependence of the TL intensity on the size of the crystals, being larger for the smallest crystals for pure LiF, and second, for Ag-doped samples the TL intensity augmented almost linearly with the Ag concentration.

Phosphate glasses doped with Dy${}^{3+}$ ions and containing silver nanoparticles (SNPs) were synthesized in the present work. We report photoluminescence characterization by absorption and emission spectra. The effect of Ag concentration on the thermoluminescence (TL) glow curves was studied. The scanning electron microscopy (SEM) shows the formation of SNP. Absorption spectra of the samples show the influence of the SNP in the bands 350nm at 425nm associated with the Dy${}^{3+}$, in the same spectra we can see the bands 750, 800, 875, 1098, 1278nm and 1675nm belonging to the Dy${}^{3+}$. Emission spectra show two prominent bands at 480nm and 574nm and one faint band at 665nm corresponding to ⁴F${}_{9∕2}{\to }^6$H${}_{15∕2}$, ⁴F${}_{9∕2}{\to }^6$H${}_{13∕2}$ and ⁴F${}_{9∕2}{\to }^6$H${}_{11∕2}$ transitions, respectively. All bands under 364nm pumping, and the fluorescence in the 550nm and 590nm spectral range enhanced four times. The Commission Internationale de 1’Eclairage (CIE) color coordinates were evaluated from the emission spectra to simulate white light emission from the phosphate glasses. The photostability of the samples was also studied in the UVA (315–403nm) and UVB (280–315nm) ranges. TL due to ultraviolet radiation (UVR) was studied; the glow curves show significant dependence of the TL intensity with the increment of SNPs in the samples. These results show the phosphate glasses doped with Dy${}^{3+}$ and containing SNP as a potential candidate have to be used in solid-state illumination and retrospective dosimetry.

In recent years, nonlinear optics field is in constant growth, particularly on the characterization and study of optical properties of glass compounds. In this sense, the plasmonic effect caused by silver nanoparticles (SNP) on the nonlinear optical (NLO) properties of different materials was studied. Furthermore, we report the experimental absorption spectra, the emission spectra, Z-scan measurements in both closed and open apertures and scanning transmission electron microscopy (STEM) to show the morphology of the matrices and the nucleation of SNP. Moreover, some NLO parameters were calculated, such as the NL refraction index and NL coefficient absorption of lithium tetraborate (Li₂B₄O₇) glass activated with rare earths (Dy³⁺ and Yb³⁺), as well as study of the effect of different concentrations of SNP. From the results obtained, it has been ascertained that the plasmon resonance caused by the presence of SNP enhances the NL refraction index value, as well as most of its linear optical properties in the matrix of Li₂B₄O₇.

ZrO₂ samples were obtained using three different synthesis methods (Calcination, Co-precipitation and Hydrothermal). The samples were characterized to analyze the effect of the crystalline phase on their thermoluminescent (TL) and photoluminescent (PL) responses. The ZrO₂ phase was analyzed by X-Ray diffraction (XRD) and Raman. Nanoparticle size distribution was obtained by scanning electron microscopy (SEM). For optical analysis, characterizations included absorbance measurements, where samples exhibited modifications in color centers, PL emission and experimental fluorescence lifetime decay (${\tau }_{exp})$ measurements. Additionally, their TL response was studied under UV (245nm and 385nm), and 6MV photon energy from LINAC excitation. The obtained results show the improvement of TL and PL properties due to ZrO₂ phase while an amorphous ZrO₂ synthesized by hydrothermal method is an excellent prospect to be used as TL material and it may be a promising scintillator material at 254nm.

A new green emitting long-lasting phosphor Ca₂ZnSi₂O₇:Eu²⁺ has been synthesized through the high temperature solid-state method. The excitation spectrum of shows a broadband attributed to ⁸S_7/2–4f⁶5d¹ transition of Eu²⁺ ions. Both of the fluorescence and phosphorescence spectra showed a broadband centered at 528 nm, corresponding the only one Ca²⁺ site in Ca₂ZnSi₂O₇. The relationship of emission wavelength and Eu–O distance is investigated. Its afterglow can be seen with the naked eye in the dark clearly for 2 h after removal of the excitation source. Oxygen vacancy and zinc vacancy , two different kinds of traps are proposed and their contrary influence on afterglow is discussed.

Trap types of the yellow emitting long-persistent phosphor Ca₂BO₃Cl: ${\text{Eu}}^{2+}$, ${\text{Dy}}^{3+}$ were analyzed in this study. ${\text{Eu}}^{2+}$ acting as luminescent centers produced a broad emission band located at 580nm, which ascribes to the 5d-4f transitions. Four kinds of traps in this afterglow phosphor were detected by thermoluminescence spectra. Electron paramagnetic resonance spectroscopy, which is a considerable testing method, was used to identify the traps caused by different reasons. Based on it, detailed processes and traps analyses were examined and discussed.

In this paper, we report on the thermoluminescence response of nanocrystalline co-doped alkaline earth aluminates synthesized by combustion method using metal nitrate as precursor and urea as fuel. A broad TL glow peak was observed at 367 K with a shoulder at 400K. TL Anal program has been used for GCD curve fitting. The Kinetic parameters like, the activation energy (E_α), the frequency factor (s) and the order of kinetics were calculated for the SrAl₂O₄: Eu²⁺, Dy³⁺nanophosphors. The best dopants combination was Eu (1 mol%) and Dy (2 mol%). The samples were irradiated with γ-dose in the range 20Gy–800Gy, at room temperature. A shift from 367 K to 376 K was also observed in the main peak with an increase in irradiation dose which suggest that the irradiation doses affect the distributions of traps produced by the gamma-ray irradiations. Kinetic parameters also suggest that TL glow curve in SrAl₂O₄: Eu²⁺, Dy³⁺ nanophosphors is obeying second order kinetics. The nanophosphors show linear response with dose.

The polycrystalline sample of SrB₄O₇ doped with copper was prepared by employing the combustion synthesis and studied for its thermo luminescence properties when exposed to Gamma-rays. The Kinetic parameters were calculated using peak shape method. The effect of dose Variation and concentration of copper on SrB₄O₇ phosphor were also studied.

Investigation on the sediment movement characteristics was conducted in a broad research area with a 150-kilometer stretch along the Enshunada Coast and the Suruga Bay, Japan based on feldspar thermoluminescence (TL) properties. River sand grains (primary source) present a higher TL signal than beach sand. Along the nearshore area, local TL intensity peaks are observed at the river mouth and sample TL intensity gradually deceases with increasing distance from the river mouth, which indicates sediment longshore transport features. Far away from the river mouth, the decreasing trend on TL intensities terminates. Taking the spatial distribution of TL intensities into account, a quantitative estimation on the longshore sediment flux was carried out based on the total river sand discharge. A sunbath test was implemented to help to distinguish the beach sand constituents. Identification of coastal sand sources was achieved in terms of the profile and magnitude of the measured TL glow curves.