Non-monotonic dose dependence of thermoluminescence

CONDUCTION BAND-VALENCE BAND THEORY OF TL AND OSL: EMPHASIS ON DELOCALIZED TRANSITIONS AND EXPLANATION ON SOME UNUSUAL EFFECTS

We discuss some unusual thermoluminescence (TL) and optically stimulated luminescence effects. We focus on luminescence due to transitions of electrons or holes through the conduction or valence band, respectively. We deal with non-linear dose dependence and non-monotonic dose dependence and also dose-rate effects sometimes reported. Also, is discussed the sensitisation of a sample due to the combined effect of irradiation and annealing, occurring in quartz samples and other materials. Another effect presented is the occurrence of anomalously high activation energies and frequency factors and its possible theoretical interpretation. Also, are considered the effects of anomalous fading and anomalous stability. Yet another phenomenon is concentration quenching. Here, the intensity of emitted TL depends non-monotonically on the concentration of the impurity responsible for the emission. The explanations given to these phenomena are based on the numerical solutions of the relevant sets of differential equations as well as approximate analytical treatment.

Thermoluminescence study of CaNa2 (SO4 )2 phosphor doped with Eu3+ and synthesized by combustion method

In the present study, the thermoluminescence (TL) properties of an Eu³⁺ -doped CaNa₂ (SO₄ )₂ phosphor were studied. The Eu³⁺ -doped CaNa₂ (SO₄ )₂ phosphor was synthesized using the combustion method. The samples were well crystallized in the monoclinic phase. The TL glow curve of the Eu³⁺ -doped CaNa₂ (SO₄ )₂ phosphor showed a single prominent peak at around 210°C with showed linearity on increasing exposure. The response curve of the synthesized phosphor showed linearity in the range 500-7000 Gy. Trapping parameters of synthesized phosphors such as activation energy, frequency factor, and order of kinetics were calculated in the study. These trapping parameters were determined by different methods such as Chen's peak method, the initial rise method, and Ilich's method. Each characteristic of these outcomes demonstrated that the synthesized Eu³⁺ -doped CaNa₂ (SO₄ )₂ phosphor had outstanding TL properties and might be valuable for TL dosimetry application.

Luminescence properties of tricalcium phosphate doped with dysprosium

Tricalcium phosphate having effective atomic number Z_eff = 15.785, equivalent to that of bones was studied for its thermoluminescence (TL) and photoluminescence (PL) properties. Different samples with varied concentrations of the dopant Dy³⁺ (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mol %) were synthesized by the chemical co-precipitation technique. Phase and compound confirmations were done using X-Ray Diffraction (XRD) and the phosphors' crystallite size was calculated using Scherrer's formula which was found to range between 27 nm and 49 nm. The surface morphological study was done using Field Emission-Scanning Electron Microscopy (FE-SEM). Other characterization techniques used for compound confirmation included Energy Dispersive X-Ray Spectroscopy (EDX) and Fourier Transform Infrared Spectroscopy (FTIR). Samples were further irradiated by gamma rays (emitted from Co-60) with dose varying from 10 Gy to 5 kGy in order to study their TL properties. Concentration optimization of the given phosphor was done in terms of its TL intensity and was found to be 0.5 mol %. The TL dose response of the phosphor was linear over a wide range of dose (10 Gy-3 kGy). Deconvolution was performed on the glow curve for 10 Gy dose, giving six peaks (at 127^o, 153^o, 185^o, 218^o, 313^o and 335^oC) suggesting the presence of six different types of traps. Other characteristics of the TL material i.e. repeatability and fading were also studied. Overall, the phosphor showed promising results for its utility in TL dosimetry. In addition to the TL, PL further confirmed the presence of dopant in the phosphor. Moreover, the dopant concentration was optimized in terms of the nanophosphor's PL intensity. The Commission International de l'Éclairage (CIE) was used to calculate chromaticity coordinates, colour rendering index and colour temperature in order to investigate the phosphor's application in white LEDs.

Role of Li+ ions on the surface morphology and thermoluminescence properties of Y2 O3 :Tm3+ nanophosphor

Y₂ O₃ :Tm³⁺ and Li⁺ co-doped Y₂ O₃ :Tm³⁺ nanopowders were synthesized using the solution combustion method for possible application in ultraviolet (UV) light dosimetry. X-ray diffraction revealed the crystallite sizes to be in the range 21-44 nm and 30-121 nm using the Scherrer equation and the W-H plot relationship, respectively. Field emission scanning electron microscopy confirmed that, after co-doping with 4 mol% concentration of Li⁺ , the particles were spherical in nature with an average size of ~30 nm. Fourier transformed infrared spectroscopy results showed bands at wavenumbers of 556, 1499, 1704, 2342, 2358, 2973, 3433, and 3610 cm^-1 that corresponded to the stretching and bending vibrations of Y-O, C=O and O-H. Thermoluminescence (TL) glow peaks for Y₂ O₃ :Tm³⁺ nanophosphors observed at 399 and 590 K were attributed to oxygen defects caused using UV irradiation. These oxygen defects firstly resulted in an increased prominent peak TL intensity for up to 270 min of irradiation and then a decrease. This was attributed to the presence of oxygen defect clusters that caused a reduction in recombination centres. The Li⁺ co-doped sample showed peaks at 356, 430, and 583 K and its intensity sublinearly increased up to 90 min and then thereafter decreased. The TL trapping parameters were calculated using computerized glow curve deconvolution methods. The Li⁺ co-doped sample exhibited less fading and high trap density under the UV radiation.