Thermoluminescence Emission Research Articles

Enhanced OSL emission from α- Al2O3 produced in the presence of halloysite nanocrystals

Aluminum oxide (Al2O3) compounds are extensively used in ionizing radiation dosimetry due to their high sensitivity when doped with carbon. However, their production is difficult and expensive, leading to much research on alternative ways to increase its sensitivity. This paper proposes a seed-mediated synthesis of α-Al2O3 by the combustion method with halloysite nanocrystals as seeds, which also have the ability to scavenge heavy metal ions. The dosimetric features were studied by radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL). Scanning electron microscopy images and X-ray diffraction patterns pointed to the halloysite nanotubes (HNT) acting as heterogeneous nucleation seeds, and as adsorber centers for the chromium ions (Cr3+), as evidenced by the decreased crystallite size and Cr3+ RL emission. Decreased TL intensity upon increasing HNT content in addition to the RL data suggested that the Cr3+ ions strongly participate in the TL emission process as a luminescent center. Remarkable 6-fold enhanced OSL area intensity and 69-fold OSL initial intensity enhancement were registered from the samples seed-mediated by HNT, revealing that, by scavenging Cr3+, the HNT eliminated a luminescent center that competes with the OSL emission. Therefore, HNTs are promising nanomaterials to enhance the sensitivity of Al2O3 dosimeters with potential application in medical physics, where a decrease in the density of concurrent luminescent centers and an increase in OSL intensity were evidenced by the presence of HNT in Al2O3.

Investigating thermoluminescence signal saturation in quartz and feldspar using emission spectrometry

Luminescence-based thermometry and dating often requires determination of the saturation level for specific signals and the corresponding dose. However, previous studies found non-monotonic dose responses for some monochromatic thermoluminescence (TL) and optically stimulated luminescence (OSL) signals from quartz as well as spectral overlap of emission bands, substantially complicating data interpretation. Therefore, the present study examines (1) the variability in the TL emission spectrum of quartz and feldspar from bedrock and sediment of different provenances and, (2) the saturation characteristics of the blue emission band for both quartz and feldspar in the dose range from 0.25 kGy to 50 kGy. The experimental results confirm differences in the spectra which appear to be characteristic of their geological origin and chemical composition. Spectral analysis shows that in the temperature range 175–220 °C the blue emission band at ∼2.5 eV dominates over other bands for all quartz samples studied. A broad UV-blue TL signal peaking at ∼2.5−3.0 eV and composed of probably three overlapping, individual bands is characteristic for K-feldspar, while one Na-feldspar exhibits an additional band at ∼2.2 eV.In the studied dose range, the emissions at ∼2.5 eV and ∼2.6 eV increase as a function of dose up to 6 kGy for both quartz and feldspar. A difference in dose response was observed for high doses (>6 kGy) where feldspar samples reached a stable saturation level while for quartz the blue emission band intensity decays until 50 kGy after having attained a maximum. Our results suggest the suitability of feldspar TL for palaeothermometry and thermochronometry from the perspective of signal saturation characteristics. However, the spectral overlap of several bands in the UV-blue emission requires careful optical filter selection to isolate the signal of interest. The non-monotonic dose response of the ∼2.5 eV emission of quartz around 200 °C glow curve temperature probably precludes its use for temperature sensing based on relative trap saturation levels.

Beta radiation-induced thermoluminescence in pure and rare earth doped ZrO2 prepared by pechini-type sol-gel

Thermoluminescence properties of ZrO2, ZrO2:Gd3+, ZrO2:Gd3+–Dy3+, ZrO2:Gd3+–Yb3+, ZrO2:Gd3+–Er3+ and ZrO2:Gd3+–Sm3+ phosphors synthesized by Pechini method were investigated. XRD measurement suggested that all the samples are monoclinic and tetragonal multiphase. Crystallite size measured using SEM is around 200 nm–250 nm. The Tmax–TSTOP, variable dose and glow curve fitting methods were applied to the phosphors and reusability, dose responses and fading characteristics were examined. The phosphors exhibit a natural TL emission which disappeared after heat treatment. The glow curves of the pure ZrO2 have thirteen individual glow peaks, which include the peaks reported for the monoclinic and tetragonal phases. Although some peaks emerge at low irradiation doses, others can only be observed at high doses. Moreover, although the dopes blanched some of the peaks of pure ZrO2, they made others more intense. These peaks can be interpreted as if they emerged caused by the rare earth doping into the matrix material. On the other hand, Gd3+, Dy3+, Yb3+, Er3+ and Sm3+ dopes did not alter the peak temperatures of the matrix material. As a result, the individual peak intensities are very sensitive to the dopes. Fundamental trapping parameters of the trap levels were calculated, and the results are in good agreement with the given values of activation energies in the literature. Fading experiments show the materials have both normal and abnormal fading characteristics in long and short-term storage.

Thermoluminescence and ATR-FTIR study of UVC-irradiated low-density polyethylene (LDPE) food packaging

This research aims to study the effects of ultraviolet C (UVC) radiation on low-density polyethylene (LDPE) food packaging. Main objectives include evaluating LDPE degradation and detecting UVC radiation using thermoluminescent dosimeters (TLDs) placed under LDPE samples. Results confirm accurate UVC detection after one hour of exposure, providing a useful tool for optimize food treatment procedures.ATR-FTIR spectroscopy analysis revealed subtle alterations (<8 % transmittance relative) in UVC-irradiated LDPE samples, including possible CH breakage (2910 and 2848 cm−1) and potential CC bond vibrations (1470 cm−1), among others. However, observed variations may stem from LDPE properties rather than entirely from UVC radiation. A comparative study of UVC-induced thermoluminescence (TL) emissions provided insights into various TLDs materials. TL kinetic analysis, using computerised glow curve deconvolution (CGCD) method, unveiled trap charge activation due to UVC exposure, including partial ionization, bleaching effect and photo-transfer (PTTL) processes. LDPE samples amplified UVC-TL responses, revealing intensity differences between the TLDs attributed to the PTTL process, accentuated by the lack of an annealing treatment. Additionally, chemical composition of the TL detectors such as, type, concentration, number, oxidation states and ionic radii of their dopants may influence UVC-TL response. Consequently, TL intensity ratios follow as: GR-200 (LiF: Mg, Cu, P) > TLD-100 (LiF: Ti, Mg) > TLD-400 (CaF2: Mn) > TLD-200 (CaF2: Dy). Thus, GR-200 detects ionizing radiation but cannot distinguish between ionizing and non-ionizing UVC radiation, while TLD-100 has limited effectiveness as a UVC radiation detector. In contrast, TLD-400 is suitable for detecting UVC radiation and TLD-200 emerges as the most favorable UVC detector, showing consistent response levels and minimal PTTL effect placed under the LDPE samples without the need of a thermal annealing treatment that makes the TLD-200 to be reusable in a low-cost measurement protocol.

Development of CaSO4:RE,Li (RE = Tm, Eu, Tb) composites for thermally or optically stimulated luminescence dosimetry

This work proposed the development of CaSO4:Tm,Li, CaSO4:Tb,Li and CaSO4:Eu,Li composites for application in radiation dosimetry, using luminescent techniques such as thermoluminescence (TL) and optically stimulated luminescence (OSL). The CaSO4 crystals were produced by the adapted slow evaporation route and characterized using X-ray diffraction (XRD), TL and OSL techniques. XRD analyses showed that the doped CaSO4 samples presented a single phase. The CaSO4:Eu,Li composites showed TL signals with peaks around 145 °C and 180 °C. The CaSO4:Tb,Li and CaSO4:Tm,Li composites showed TL signals with peaks centered at 165 °C and 275 °C. For the CaSO4:Tb and CaSO4:Tm samples, the addition of lithium as co-dopant resulted into a significant increase (2x) in the total TL signal of the samples. The CaSO4:Tm,Li samples presented a very intense OSL signal, about 80x greater than the signal of the other samples produced. This allows the applicability of TL/OSL detectors even more sensitives. The TL emission spectra of the samples showed typical emissions of Eu2+ ions (280 nm), Eu3+ (614 nm), Tb3+ (544 nm) and Tm3+ (455 nm). No emission corresponding to lithium was identified. All the samples produced showed linearity in the dose range used and good reproducibility, with variations below 10%. The CaSO4:Tm,Li samples showed the lowest limit of detection and fading. The evaluated dosimetric characteristics denote that these developed composites have potential application as TL/OSL detectors.

Assessing whether a thermoluminescence peak at ∼100 °C in calcitic opercula can be used to monitor thermal reproducibility

The opercula of the gastropod Bithynia tentaculata is composed of calcite and exhibits three main thermoluminescence peaks at ∼100, 280 and 360 °C when heated at 0.5 °C.s−1. The two higher temperature peaks can be used for geological and archaeological dating, whilst the lower temperature peak has a lifetime of hours and is only seen after laboratory irradiation. This study explores whether this lower temperature TL peak can be used to assess the reproducibility of laboratory heating of opercula. As found in previous studies, the TL peak at ∼100 °C is seen to consist of at least two signals which have different lifetimes at room temperature. By fixing the interval between irradiation and measurement of the TL signal, the impact of these different lifetimes on the temperature at which the TL peak occurs (Tm) can be reduced, and replicate measurements on a single operculum using the same radiation dose yield values of Tm within 1 °C. Comparison of different opercula shows variation in Tm of 9 °C when heating at 5 °C.s−1, interpreted as primarily arising from variation in thermal lag between the hotplate and the different samples assessed. Reducing the heating rate to 0.5 °C.s−1 reduces the variation in Tm between opercula to 2 °C. Imaging the TL emission from opercula using an EMCCD shows spatial variation in heating, and also demonstrates the reduction in variability that can be achieved by using a slower heating rate. Thus, monitoring the position of the TL peak at ∼100 °C can be used to assess thermal reproducibility of TL measurements on calcitic opercula.

Evaluation of TL and OSL signals of MgB4O7:Tm,Li prepared by the solution combustion method

Magnesium tetraborate (MgB4O7) doped with rare-earth elements is recognized for its suitability in thermoluminescence (TL) dosimetry due to its low effective atomic number (Zeff = 8.4) and the potential applications in neutron dosimetry. The study investigates the luminescent (TL and OSL) properties of MgB4O7 doped with thulium (Tm3+) and lithium (Li+). Samples were synthesized using the solution combustion method and TL and OSL responses were evaluated using a spectrometer and an automated OSL/TL reader. The emission lines of Tm3+ are consistent with previous literature, with Li+ enhancing TL and OSL responses. TL emission spectra unveil distinct bands corresponding to [Tm3+]* transitions. The electron paramagnetic resonance (EPR) spectroscopy analysis carried out in unirradiated, irradiated and annealed samples.The results show that the signals corresponding to BO32− and O2− are seen upon irradiation and disappear after annealing at 200 °C, indicating the participation of these centers in the TL process. The results show that the TL response of MgB4O7:Tm,Li is much more sensitive to gamma radiation than MgB4O7:Tm, with a minimum detectable value of 0.084 mGy and a linear response with dose for the range studied, from 0 to 500 mGy, with R2 of 0.998.

Thermoluminescence (TL) and electron paramagnetic resonance (EPR) of dumortierite sensitized by heat treatments

The present study presents the effect of heat treatment on TL and EPR of dumortierite. It was found that applying a heat treatment at 1200 °C for 1h, followed by slow cooling to room temperature, is optimal for improving its TL sensitivity. The glow curves of the sensitized dumortierite sample show TL emission bands centered at 350, 475, and 580 nm. The kinetic parameters of the TL peaks were obtained using the Tm-Tstop and deconvolution methods. In addition, sensitized dumortierite exhibits a linear response with γ-radiation dose and low fading in its TL response. Studies using the technique of EPR were carried out to investigate the defect center EPR signals observed after γ-irradiation. A single defect center with an axially symmetric g-tensor was observed with principal values g∥ = 2.0009 and g⊥ = 2.0017. The center was attributed to an F+ center and appears to correlate with the TL peak at 200 °C.

Thermoluminescence characteristics of gamma-irradiated nano-alumina

The focus of this study lies in exploring the properties of thermoluminescence (TL) in nano-alumina, including the correlation between TL intensity and absorbed dose, identification of individual luminescence peaks, and investigation of trap parameters for potential dosimetry applications. The samples were irradiated by 60Co with doses ranging from 530 to 2646 Gy. Micro-sized α-Al2O3 had a prominent dosimetry peak at maximum temperature Tm = 435 K. Nano-α-Al2O3 samples with 40 and 50 nm particle sizes exhibited a TL luminescence glow curve, with the main dosimetry peak in the low-temperature region and a complex structure at higher temperatures (above 500 K). The observed maximum of the main dosimetry peak depended on the nanoparticle size and was 460 K for the sample with particle size of 40 nm and 467 K for 50 nm. The main dosimetry peak was described by the superposition of the two peaks.A computerized glow curve deconvolution method was applied to determine the parameters of the traps responsible for TL using the Microsoft Windows-operated GlowFit program, assuming first-order kinetics. The found values of the activation energies were 0.97 ± 0.01 eV for the trapping center responsible for the peak with Tm = 458 ± 3 K and, accordingly, 1.05 eV for the peak with Tm = 473 ± 3 K. The estimated values of the frequency factor were s ≈ 1.01 × 1010 and 1.3 × 1010 s−1 for the peak with Tm = 458 ± 3 K, and 2.06 × 1011 s−1 for the peak with Tm = 473 ± 3K, respectively. The lifetime for the traps in nano-α-Al2O3 was estimated as 43–56 days for the first trap and approximately 65 days for the second trap. It is assumed that these traps are responsible for TL emission at the low-temperature part of the glow curve.

Effects of UVC irradiation on polystyrene for healthcare packaging: Study by FTIR and Raman spectroscopy with thermoluminescence

The interaction between ultraviolet C radiation (UVC) and polystyrene (PS) materials has been investigated, particularly in post-packaging irradiation processes for healthcare applications. Effective UVC penetration through PS materials, regardless of their thickness (0.16 and 0.40 mm) has been observed. However, the penetration effectiveness could be affected by the thickness of the PS material. Achieving optimal post-packaging UVC treatment requires a thorough evaluation of chemical composition and material thickness, especially in pharmaceutical and medical packaging industries.Preliminary results reveal minimal degradation in UVC-irradiated PS packaging samples, as supported by FTIR and Raman spectroscopy characterization. Minor variations could be attributed to intrinsic PS materials properties and/or their respective background, rather than the influence of UVC radiation. Consequently, PS materials exhibit resilience under the experimental conditions following UVC irradiation treatment. Furthermore, a comprehensive analysis of thermoluminescence (TL) emissions evaluates several commercial dosimeter materials for UVC radiation detection. The TLD-100 and TLD-200 dosimeters show potential as UVC detectors, displaying distinct responses linked to the non-ionizing component of UVC radiation at 310 °C and in the range of 150–250 °C, respectively. However, the TLD-400 and GR-200 dosimeters are not suitable for UVC detection due to their spread TL emissions considering intensity and curve shape.This UVC-TL analysis consistently detects radiation in the proposed commercial dosimeter materials one-hour post-exposure, providing assurance that healthcare materials have been irradiated. Such analysis enhances reliability during extended UVC exposures, offering valuable insights for industries employing UVC-irradiated materials, particularly in healthcare applications.

Study of the centers responsible for the TL emission by EPR and PL analysis of Eu-doped CaSiO3 phosphors synthesized by the devitrification method

CaSiO3 doped at different ppm of Eu were synthesized by the devitrification method. Polycrystals exhibit a prominent high-temperature TL peak that increases in intensity and shifts toward higher temperatures with increasing amounts of dopant. TL emission spectrum of CaSiO3: Eu displays two very broad bands centered at 400 and 440 nm corresponding to the temperatures of 229.5 and 373.5 °C, respectively. PL measurements indicate the presence of Eu2+ and Eu3+ ions. EPR spectrum arises from two defect centers. One of the centers with principal g-values 2.016, 2.0091, and 2.0051 is attributed to O− ion and the center correlates with the TL peak at 236 °C. Center II with an isotropic g-value of 2.0018 is attributed to an F+ center and the center relates to the TL peak at 120 °C. Center III is also tentatively identified as the F+ center which is associated with the TL peak at 365 °C.

Luminescence Properties of Ce-Doped Di-Calcium Magnesium Disilicate Ca2MgSi2O7:4 mol%Ce

Dicalcium magnesium disilicate (Ca2MgSi2O7) doped with cerium rare earth ions has been examined for its optical and photonic characteristics and applicability for radiation dosimetry applications. Mono-calcium aluminate that has cerium added to it, has been shown to be an excellent dosimeter with a linear response up to roughly 4 kGy of radiation exposures. Maximum TL emission is achieved at 4 mol% cerium dopant concentration. The clearly visible two peaks that were detected at 381.13K and 566.87K can be used as a high-temperature dosimetry advance. In this study, we reported the preparation technique and luminescence properties such as TL, ML, and PL of Ce3+ doped dicalcium magnesium silicate phosphors. The phosphors were prepared by the solid-state reaction method. The TL glow curves were recorded for all different concentrations of Ce- doped phosphors.

Thermoluminescence characteristics of unannealed and a high temperature annealed green beryl

The thermoluminescence characteristics of natural green beryl are reported. Aliquots of the sample used were irradiated using a beta source at a dose rate of 0.1 Gy/s. The glow curves measured at 1 °C/s from aliqouts irradiated to a dose of 1 Gy have peaks at 74, 166, 280 and 422 °C. Only the peak temperature value of the peak at 166 °C is dose dependent, changing from 158 °C for aliquot irradiated to a dose of 0.1 Gy to 190 °C for aliquot irradiated to a dose of 100 Gy. Tm-Tstop and GCD analyses revealed that the peak which appears at 166 °C consists of two overlapping components near 165 and 187 °C. All the peaks are affected by thermal quenching to varying degrees. Activation energy values of the glow peaks calculated using GCD and E-Tstop analyses are in good agreement. Exposure of pre-irradiated beryl to light bleaches luminescence stored in it by the irradiation. TL emission in natural beryl may be dependent on previous thermal history in the environment.

Identification of defect centers responsible for thermoluminescence emission in sol-gel synthesized calcium silicate phosphor

The thermoluminescence (TL) of calcium silicate phosphor (CSO) prepared by the sol-gel method and sintered at 1200 °C were investigated. From Tm-Tstop curve, TL emission spectrum and computer deconvolution using electron traps with discrete and continuous distributions, the glow curves were found to be composed of four TL peaks (117, 190, 250 and 275 °C) with a single emission band centered at 370 nm. Electron paramagnetic resonance (EPR) investigation has been carried out to identify the defect centers formed in the CSO phosphor by γ-irradiation and find the centers related to the TL process in the phosphor. At room temperature, three defect centers were observed. The first center, characterized by the principal g-values of 2.014, 2.011, and 2.0080 was assigned to an O− ion. The second center with g-values 2.015, 2.013, and 2.010 is also attributed to an O− ion and is associated with the TL peak at 280 °C. The third center, with an isotropic g-value of 2.0011 was identified as the F+ center (singly ionized oxygen vacancy) and relates to the TL peak at 280 °C.

Photoluminescence and thermoluminescence properties of pure and rare-earth-doped ZrO2 prepared by Pechini-type sol-gel.

In this article, photoluminescence (PL) and thermoluminescence (TL) properties of ZrO2 , ZrO2 :Dy3+ , ZrO2 :Dy3+ -Gd3+ , ZrO2 :Dy3+ -Yb3+ , ZrO2 :Dy3+ -Er3+ , and ZrO2 :Dy3+ -Sm3+ phosphors synthesized by the Pechini method were investigated. The crystal structure, thermal properties, morphology, PL and TL properties were investigated using X-ray powder diffraction (XRD), differential thermal analysis/thermogravimetric analysis (DTA/TGA), scanning electron microscopy (SEM), PL and TL, respectively. The room temperature emission bands corresponding to 4 F9/2 →6 HJ (J= 9/2, 11/2, 13/2 and 15/2) transitions of Dy3+ ions were measured. The phosphors were analysed using Tm -TSTOP , variable dose, and computerized glow curve fitting methods. Reusability, dose-response, and fading characteristics were investigated. The phosphors have a natural TL emission that vanished by heating treatment. Moreover, new peaks with similar properties to the natural emissions were observed after high-dose irradiation and long-term fading experiments. The glow curves of the phosphors have 13 individual peaks and many low- and high-temperature satellite peaks. The origin of the peaks is ZrO2 host material and doping with rare-earth ions (Gd3+ , Dy3+ , Yb3+ , Er3+ and Sm3+ ) does not lead to a new glow peak. The dopants cause drastic changes in individual peak intensities of ZrO2 .The initial fading rates of all the phosphors are relatively fast, but they slow down as time goes on.

TL, OSL, EPR, and defect centers in Tb-doped strontium silicate phosphor synthesized by a solid-state reaction method

Strong thermoluminescence (TL) was observed in Tb-doped strontium silicate phosphor prepared by the solid-state reaction method. Two glow peaks are observed at 100 and 190 °C. TL emission spectra indicate three recombination centers. The number of peaks and the kinetic parameters associated with the TL glow peaks of Tb-doped Sr2SiO4 phosphor after gamma irradiation were analyzed by Tm-Tstop and deconvolution methods. A study of defect centers induced by γ-irradiation and identification of defect centers responsible for the observed TL glow peaks has been carried out using the electron paramagnetic resonance (EPR) technique. The observed spectrum at room temperature is a superposition of at least three defect centers. Center I is characterized by an axially symmetric g-tensor with principal values g|| = 2.019, and g⊥ = 2.0013 and is ascribed to a O2− ion. Center II has a rhombic g-tensor with principal values 2.0072, 2.0024, and 1.995 and is assigned to an F+ center (singly ionized oxygen vacancy) and correlates with the 190 °C TL peak. The third center (center III) has an isotropic g-value of 1.991 and is identified as an F+ center.

Effect of Pr doping on structure and luminescence properties of ZrO2 nanoparticles

Pr3+ impurity transitions in monoclinic and cubic phases of ZrO2 have been investigated by photoluminescence and thermoluminescence (TL). Zr(1−x)Pr x O2 (0 ⩽ x ⩽ 0.015) samples were prepared by the combustion method. Rietveld refined x-ray diffraction results confirm that undoped ZrO2 has a monoclinic structure, whereas Pr doped ZrO2 samples are in mixed phase consisting of monoclinic and cubic structures. ZrO2 shows a broad defect-related emission peak centered at 500 nm under an excitation wavelength of 300 nm. A series of Pr3+-related emissions are observed at 512, 584, 612–640 nm due to 3P0 → 3H4, 3P1 + 1I6 → 3H5, 1D2 → 3H4 transitions and between 719 and 740 nm due to 1D2 → 3H5 transitions when excited with 454 nm. The PL decay lifetime of Zr0.996Pr0.004O2 is 1.55 μs for fixed λ ex = 300 nm and λ em = 612 nm. The TL glow curve of Zr0.99Pr0.01O2 shows a prominent peak at 695 K and secondary peaks at 508 K and 570 K, which are not observed in undoped ZrO2. The TL emission measured at 695 K confirms that Pr3+ replaces Zr4+ in cubic lattice sites of ZrO2. This work shows the relationship between the luminescence properties and different structures of ZrO2 and that supports the design of new materials for possible applications.

Thermoluminescence mechanism of microwave combustion synthesized γ-irradiated Al2O3:Tm3+ phosphor

The thermoluminescence (TL) mechanism of γ-irradiated Al2O3:Tm3+ phosphor is presented in this paper. Al2O3:Tm3+ phosphors are synthesized by muffle furnace combustion (MFC) and microwave combustion (MWC). XRD results exhibit the stable alpha phase of Al2O3 and crystallite size is found to be ∼99 and ∼147 nm for MFC and MWC synthesized samples respectively. The optical band gap (Eg) of MFC and MWC synthesized Tm3+-doped materials is found to be 4.27 and 4.31 eV, respectively using DRS. TL glow curves of γ -irradiated Al2O3:Tm3+ phosphor are recorded for the dose ranging from 0.1 to 20 Gy. TL glow curves of γ - irradiated phosphor show a prominent peak at ∼453 K along with a shoulder at ∼500 K. The prominent TL glow peak (455 K) intensity of MWC synthesized Al2O3:Tm3+ is ∼2.56 times higher than MFC synthesized phosphor. The TL emission spectra of 455 K glow peak show emission at 298, 355, 394, 466, 526, and 658 nm corresponding to the 1I6→3H6, 1D2→3H6, 3P2→3H4, 1G4→3H6, 1D2→3H5 and 1D2→3H4 characteristic transitions of Tm3+. TL emission spectrum exhibits Cr3+ (R-lines) and Mn4+ characteristic emission peaks at 453 K along with Tm3+ emission. TL intensity of the MWC synthesized sample's prominent peak at 453 K increases linearly with a dose from 0.1 to 15 Gy and then it increases super-linearly with a dose up to 20 Gy. The kinetic parameters were calculated and the process of ionization of electrons from Tm3+, electron trap in host lattice, and its recombination mechanism is proposed.

The Effect of a Yb Co-Dopant on the Blue Upconversion and Thermoluminescent Emission of SrLaAlO4:Yb3+,Tm3+ Phosphors

In this study, we described the structural, morphological, optical, photoluminescence, and thermoluminescence properties of SrLaAlO4:Tm3+,Yb3+ (SLAO:Tm,Yb) blue-emitting phosphors made by combustion synthesis and a post-annealing treatment at 1200 °C. The Yb co-dopant concentration was varied (1.0, 3.0, 5.0, and 6.0 mol%) while the Tm dopant concentration was fixed at 5 mol%. According to the X-ray diffraction patterns, all the samples presented the pure tetragonal phase of SrLaAlO4. Scanning electron microscopy analysis showed that the SLAO powders had morphologies of irregular or bar grains with average sizes in the range of 0.5–1.07 µm. Photoluminescence emission under 980 nm excitation showed an intense blue emission peak at 481 nm. The phosphors also emitted red light at 654 nm and a prominent NIR emission at 801 nm. All those emissions correspond to 1G4 → 3H6, 1G4 → 3H4 and 3H4 → 3H6 transitions of Tm3+. The SLAO:Tm,Yb phosphors synthesized with 3.0 mol.% of the Yb co-dopant showed the highest emission intensity in the visible/near-infrared (NIR) range (400–800 nm), and its CIE coordinates corresponded to the blue color (0.19368, 0.15826). Additionally, thermoluminescence emissions were recorded for the SLAO:Tm,Yb phosphors. The samples were previously irradiated with UV wavelengths of 265 nm, 365 nm, and 385 nm prior to the thermoluminescent measurements. After this, the kinetic parameters such as frequency factors, activation energy (E), and order of kinetics were calculated using the Chen method. The thermoluminiscent emissions demonstrated that the SLAO:Yb,Tm phosphors can be used for UV dosimetry.

Investigation of dosimetric properties of CaSO4:Mn phosphor prepared using slow evaporation route

The objective of this work was to investigate the luminescent properties of CaSO4:Mn synthesized by slow evaporation route. The crystalline structure, morphology, thermal and optical properties of the phosphors were characterized by X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), photoluminescence (PL) and thermogravimetric analysis (TGA). Moreover, using thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques, the dosimetric properties of the phosphors, such as emission spectra, glow curve reproducibility, dose-response linearity, fading of the luminescent signal, variation of the TL intensity with the heating rate, OSL decay curves, correlation between TL and OSL emissions and minimum detectable dose (MDD) were comprehensively investigated. For dosimetric analyses, the samples were irradiated with doses from 169 mGy to 10 Gy. The emission band fits with the characteristic line of the Mn2+ emission features, ascribed to 6A1→4T1 transition. CaSO4:Mn pellets present a TL glow curve with a single typical peak centered around 494 nm, an OSL decay curve with predominance of a fast decay component, and a MDD on the order of mGy. The luminescent signals showed to be linear and reproducible in the studied dose range. The trapping centers located between 0.83 eV and 1.07 eV were revealed for different heating rates in the TL study. The high TL sensitivity of CaSO4:Mn was proven when comparing with commercially available dosimeters. The luminescent signals exhibit a smaller fading than described in the literature for CaSO4:Mn produced by other methods.