Thermoluminescence Measurements Research Articles

Luminescence properties of Ce-doped ZrO2 phosphors synthesized by combustion method.

Zr1-x Cex O2 with x = 0.005, 0.01, 0.02, and 0.03 samples were synthesized using a combustion technique. The X-ray diffraction results revealed that Ce-doped ZrO2 nanoparticles were in a monoclinic structure up to 1mol% Ce concentration. The increase in the Ce concentration caused more distortion in the monoclinic structure of zirconia. The samples showed a mixed phase (monoclinic + tetragonal) beyond 1mol% Ce content. The crystallite size (D) and strain (ε) were calculated from the Williamson-Hall equation. The D decreased from 25 ± 1 to 20 ± 1nm and ε increased from 0.03 to 0.28% with an increase in Ce concentration. Photoluminescence (PL) spectra of Zr1-x Cex O2 showed emission in the blue region under an excitation wavelength of 290 nm. Zr0.995 Ce0.005 O2 showed the highest PL intensity with an average lifetime of 0.93 μs, and the PL intensity decreased with the increase in the Ce concentration. Thermoluminescence (TL) glow curves of Zr1-x Cex O2 were measured after gamma irradiation (500 Gy) with a heating rate of 5K s-1 . The TL curve of Zr0.995 Ce0.005 O2 showed two prominent peaks at 412 K (peak 1) and 600 K (peak 2). The first TL glow peak was shifted towards a higher temperature at 440 K above 1mol% Ce concentration. Repetitive TL measurements on the same aliquot exhibited excellent repeatability. Kinetic parameters associated with the TL peaks were calculated using the curve fitting method. Peak 1 followed non-first-order kinetics. The value of the activation energy of the 440 K peak was found to be 0.95 ± 0.01 eV for Zr0.99 Ce0.01 O2 . These findings showed that Zr1-x Cex O2 might be used in lighting and radiation dosimeter applications.

Thermally Assisted Optically Stimulated Luminescence (TA-OSL) from Commercial BeO Dosimeters.

BeO is another luminescent phosphor with very deep traps (VDTs) in its matrix that could not be stimulated using either thermal or conventional optical stimulations. The present study attempts to stimulate these traps using thermally assisted optically stimulated luminescence (TA-OSL), a combination of simultaneous thermal and optical stimulation that is applied to the material following a thermoluminescence measurement up to 500 °C. An intense, peak-shaped TA-OSL signal is measured throughout the entire temperature range between room temperature and 270 °C. This signal can be explained as the transfer of charges from VDTs to both dosimetric TL traps. Experimental features such as the peaked shape of the signal along with the presence of residual TL after the TA-OSL suggest that recombination of TA-OSL takes place via the conduction band. Isothermal TA-OSL is not effective for extending the maximum detection dose thresholds of BeO, unlike minerals such as quartz and aluminum oxide. Nevertheless, TA-OSL could be effectively used in order to either (a) control the occupancy of VDTs, circumventing the intense sensitivity changes induced by long-term uses and high accumulated dose to the VDTs, or (b) measure the total dose accumulated over a series of repetitive dose calculations.

Thermochronometry of metamorphic rock complexes on the SE Peloponnese, Greece, using thermoluminescence (TL): preliminary experiments

Here, we report preliminary results from thermoluminescence (TL) measurements on metamorphic quartz from the SE Peloponnese, Greece, and we discuss its potential for thermometric and, possibly, thermochronometric applications over longer geological periods. Extensive high pressure/low temperature (HP/LT) schists associated with a 24 Ma metamorphic age, and with cooling ages ranging between 6-14 Ma (based on fission-track and (U-Th)/He thermochronometry), encompass sizable quartzite outcrops associated with substantially low radiation (U, Th, K concentrations below the analytical detection limits), allowing TL signal to grow on longer geological timescales. Although deeper TL traps (>360°C) appeared saturated as expected, geologically stable traps lying between around 360°C were found to be far from saturation. Once higher analytical resolution is achieved in the determination of the radioelement concentrations the recovered equivalent doses will be combined with the respective dose rates to explore the suitability of TL from quartz for longer-range thermochronometry in extremely low-radiation geological environments.

UV-light activated blue-emitting persistent luminescence of CaYGaO4:Bi3+ suitable for high-temperature environment

The persistent luminescence (PersL) materials suitable for high-temperature environments have attracted extensive attention in recent years. Herein, we have reported a novel long-persistent luminescent material of CaYGaO4:Bi3+, with a peak wavelength of 430 nm and a duration of more than 40 min at room temperature at the 0.32 mcd/m2 threshold value after UV irradiation. A series of thermoluminescence measurements reveal that the CaYGaO4:Bi3+ phosphor has abundant shallow and deep traps with a wide range of distribution. In addition, we utilize the ion substitution strategy of Sr2+ partially replacing Ca2+ ions to increase the shallow trap concentration, so as to improve the performance of PersL at room temperature. More importantly, we investigate the PersL performance of CaYGaO4:Bi3+ phosphor at high-temperature environment. As the result demonstrates, when the ambient temperature is in the high-temperature range (450 K–600 K), the phosphor has more obvious brightness. Finally, we take advantage of the phosphor to carry out a demonstration experiment and obtain a set of temperature-related color conversion images, which unequivocally signifies that the phosphor has broad application prospects in anti-counterfeit fields and emergency indicator marks in high-temperature and harsh environments.

New perspectives on traps and radiative recombination centers for optically stimulated luminescence in LiF:Mg,Cu,P

LiF:Mg,Cu,P (MCP) is well-known for its high thermoluminescence (TL) sensitivity and is widely used for TL dosimetry. Following recent studies, highlighting its optically stimulated luminescence (OSL), the properties of MCP have been studied for OSL-based 2D and 3D dosimetry. Here, we have measured the spectrally resolved OSL emission as a function of stimulation time, identifying the peak of the emission band to be at ∼355 nm during the early stimulation period before shifting to peaking at ∼382 nm during the remaining part of the experiment. By assuming the spectra to originate from radiative recombination centers with Gaussian emission bands, we identified two recombination centers with emission centered at ∼355 nm (RC1) and ∼394 nm (RC2), respectively. From the OSL decay curves, we have identified two dominating types of OSL traps (fast and slowly decaying OSL traps). We provide indicative values for the photoexcitation cross section of these OSL traps. The fast-decaying OSL traps were found to predominantly emit OSL through RC1. By depleting the fast-decaying OSL traps before TL measurements, we have identified these traps to be associated with a previously undetected TL peak at ∼87 ° C (1 °C/s heating rate), located between the TL peaks usually denoted as peaks one and two. We further found that the features related to the fast-decaying OSL traps were not observable for powder samples without a heat treatment at ∼560–700 °C. Pellet samples show these features without the heat treatment, but could potentially have undergone a similar treatment during sintering.

Interaction of lanthanide and actinide with BaHfO3 perovskite: A case study with cerium and uranium

AbstractSpeciation of actinide (An) and lanthanide (Ln) in technologically important ceramics is very important from both fundamental as well as technological aspects. The intrinsic structural flexibility of perovskite containing AO6 and BO12 polyhedra makes them suitable and rich hosts for An and Ln. In this work, emphasis was given to deciphering information such as oxidation state, local dopant site, charge compensating defects, excited state kinetics, and so forth in BaHfO3 (BHO) related to dopant uranium (BHO‐U) and cerium (BHO‐Ce). Several spectroscopic techniques namely, time‐resolved photoluminescence (TRPL), positron annihilation lifetime spectra (PALS), and thermoluminescence (TL) spectroscopy coupled with density functional theory (DFT) were employed to probe the same. Ce and U though are distributed at both Ba and Hf sites, Ce prefers the former, while U prefers the latter site. Uranium on the other hand stabilizes as U6+ in the form of octahedral uranate ion giving green emission. PALS suggested the formation of defects in BHO‐Ce and BHO‐U with oxygen vacancies predominating in the former whereas BHO‐U perovskites are loaded with cation vacancies and vacancy clusters. These cation vacancies are responsible for lower TL output in BHO‐U. TL measurements also suggested cerium doping leads to a higher density of deeper traps in BHO‐Ce compared to uranium doping in BHO‐U which is in concurrence with DFT results and may have implications in designing afterglow phosphors based on perovskite. We believe this work would have a long‐term impact on exploring the potential of perovskite for nuclear waste host and afterglow phosphors applications.

Urea Glass Route as a Way to Optimize YAGG:Ce3+,Cr3+,Pr3+ Nanocrystals for Persistent Luminescence Applications.

A new approach for the synthesis of Y3Al2Ga3O12 (YAGG) nanophosphors allowing the preparation of crystallites with sizes starting from 45 nm is presented. The controllability of the energy and trap density of the resulting material samples by annealing temperature was confirmed by thermoluminescence (TL) measurements. It has been shown that the annealing of samples at temperatures up to 1300 °C does not cause any substantial growth of crystallites, still remaining below 100 nm, but leads to changes in the activation energy of the persistent luminescence (PersL) process. On the other hand, annealing above 1400 °C results in grain growth on the submicron scale, which was confirmed by X-ray powder diffraction (XRPD) and electron transmission microscopy (TEM) measurements. In addition, with an increase in the molar ratio of urea to the total amount of metals used (R), qualitative changes are observed in the PersL process occurring from the excited states of Cr3+ and Pr3+ ions. This proves the influence of the synthesis process, in particular of the metal complexation at its initial stage, on the final structure ordering in the annealed materials. These observations are linked to previously reported defects in the YAGG structure, leading to PersL.

(M,Ca)AlSiN3:Eu2+ (M=Sr, Mg) long persistent phosphors prepared by combustion synthesis and applications in displays and optical information storage

Eu2+-doped CaAlSiN3‐type structure nitrides have been extensively studied as a red-emitting phosphors in white light emitting diodes (w-LEDs), but there are few reports of systematic research on the effect of solid solution substitution on their long persistent luminescent properties. In this work, a series of (M,Ca)AlSiN3:Eu2+ (M = Sr, Mg) phosphors have been successfully synthesized by efficient combustion synthesis. We investigated the effect of Sr and Mg solid solution on long persistent luminescent properties. Thermoluminescence (TL) measurements were performed in those persistent phosphors to obtain direct experimental results on the trap depth. The results show that the SrAlSiN3:0.2 at% Eu2+ phosphor exhibits the most intense red persistent luminescence with the persistent time of as long as 200 min at the threshold value of 0.32 mcd/m2 due to the presence of more trap levels with suitable depths of 0.71 eV. Compared with the solid solution of Sr, the solid solution of Mg ions can increase the depth of trap levels in CaAlSiN3. Among them, Mg0.2Ca0.8AlSiN3:0.2 at% Eu2+ phosphor achieved a maximum trap depth of 0.98 eV, making it a promising candidate for optical information storage applications.

Low temperature luminescence and tunnelling effect in the Sr4Al14O25 co-doped with Eu2+and Dy3+ persistent luminescent phosphor

Thermoluminescence (TL) technique is very useful in the research of persistent Luminescence (PL) phosphors. It gives information about the existence of energy levels within the forbidden band and lifetime. The TL glow curve of Sr4Al14O25: Eu2+,Dy3+ persistent phosphor consists of two well-separated glow peaks at around 353 K and 438 K after both UV radiation and beta irradiation. To study the low temperature (≤ room temperature) glow peaks, low temperature TL (LTTL) measurements were performed with a homemade system after exposed to UV radiation. The sample was heated according to T(t)=T∞−(T∞−T0)e−αt equation starting from liquid nitrogen temperature, 77K. Besides the peaks at around 345 and 445 K according to LTTL results, Sr4Al14O25: Eu2+,Dy3+ has two more well-separated low temperature TL peaks at around 170 K and 295 K.The lifetime of the TL glow peaks (at 353 K and 438 K) was calculated according to s−1exp(EkT) and the results were checked with fading tests. Moreover, TL sensitivity tests were carried out both with and without preheating. Finally, tunnelling effect was evaluated by using the results of sensitivity tests and fading tests. Interesting results were observed at sensitivity tests performed with preheating. The results indicates that the behaviour of two glow peaks is very different from each other. The mechanism behind the peak around 438 K is localised transition involving a tunnelling effect.

Potential of afterglow zirconia as a sensitive biological temperature probe

Noninvasive and site-selective temperature sensing is required in biology and advanced medicine. Recently, we proposed a new concept for temperature sensing, which is based on afterglow and optically-stimulated luminescence [Sci. Rep. 10, 2242 (2020)]. Here we assessed the thermal sensitivity of afterglow zirconia and clarified the potential of this material as probe phosphor by thermoluminescence measurements. The evaluated sensitivity value of the zirconia was 10 %/K, which was higher than typical materials used in luminescent thermometers. Therefore, the prepared zirconia is a great candidate as a harmless and biocompatible sensing probe.

Effects of composition and reduction conditions on persistent luminescence of SrAl2O4:Eu,Dy prepared via a solid-state reaction

SrAl2O4:Eu,Dy is a representative persistent luminescent phosphor that has been widely investigated. However, the mechanism of its long-lasting action has not been fully elucidated. With the aim of providing new insights into trapping in the phosphor by elucidating the relationship between trap creation and preparation conditions, SrAl2O4:Eu,Dy phosphors with different nominal Sr:Al compositions were prepared via a solid-state reaction and heating under different reducing conditions. The photoluminescence (PL) and persistent luminescence (PersL) emission and excitation spectroscopy of the phosphors, as well as their afterglow and thermoluminescence (TL) characteristics, were studied. SrxAl2O4:Eu2+,Dy3+ with x = 0.79–0.89 prepared via preheating in air and post-reduction showed the best afterglow properties. The PersL excitation spectra of these phosphors featured the same characteristic peaks, which were attributed to oxygen vacancies (electron traps) induced by Sr deficiencies. The TL measurements revealed that co-doping with Dy3+ ions increased the number of trapped electrons in pre-existing oxygen vacancies with trap depths of ∼0.53 eV and stabilized traps with depths of ∼0.61 eV via interactions with pre-existing oxygen vacancies that increase in number with Sr deficiency and preheating in air.

Development of cryogenic thermoluminescence measurement system and performance test on Na2W2O7 single crystal

Development of cryogenic thermoluminescence measurement system and performance test on Na2W2O7 single crystal

Alexandrite: investigation of a natural material for radiation dosimetry

In this work we performed experimental analyses of the dose-response curves of natural alexandrite, using thermoluminescence (TL) and optically stimulated luminescence (OSL). The natural alexandrite crystals from Bahia, Brazil, were pulverized and the optical absorption measurements were carried out in the range of 200 to 800 nm, comparing a non-irradiated sample with a 10 Gy beta irradiated one. OSL and TL measurements were performed using the Risø equipment (model DA-20) with irradiation doses from 1 to 5 Gy. Glow curve analysis was done using GlowFit software for TL, and R Studio software for OSL measurements. The irradiated sample (10 Gy) shows an absorption spectrum similar to the non-irradiated one, containing the same bands. The samples of natural alexandrite showed a linear dose-response for both OSL and TL measurements. From the TL and OSL analyses, it was possible to infer a correlation between the slow OSL component with the most intense TL peaks of alexandrite.

Study of thermally and optically stimulated luminescence in LiF:Mg,Ti following neutron and beta irradiation

The results reported herein were motivated by the potential application of combined optically stimulated (OSL) and thermoluminescence (TL) measurements for separation between the beta and neutron dose components in mixed neutron-beta radiation fields. The advantages of OSL/TL are two-fold: (i) The OSL and TL readout can be carried out on the same sample and (ii) the greater efficiency of OSL to high ionization density (HID) radiation due to the excitation of F2 and F3 + centers. The beta calibration coefficients for LiF:Mg,Ti (TLD-700) were measured using a 90Sr/90Y source calibrated at the Soreq Nuclear Research Center nuclear facility. The estimation of the neutron calibration coefficients was carried out by irradiation with broad beam fast neutrons of median energy 5 MeV and a quasi-monoenergetic neutron field of mean energy 14.8 MeV at the Physikalisch Technische Bundenanstalt. The preferential excitation of OSL following HID irradiation has been demonstrated.

Thermal Annealing Effect on the Thermoluminescence Properties of Commercial High‐Pressure High‐Temperature Diamond Powders

Diamond applications as thermoluminescence (TL) radiation detectors and dosimeters are extensively studied, especially in synthetic chemical vapor deposition (CVD) and high‐pressure high‐temperature (HPHT) diamonds. Herein, a comparative study of the thermal annealing (TA) effect on the TL properties of four samples of commercial HPHT microdiamonds (MD) powder with a 10–600 μm‐sized range purchased from PlasmaChem is reported. The TL measurements and irradiations are performed using a RISØ TL/OSL reader (β‐radiation, 90Sr/90Y). The TL glow curve analysis and dose behavior are studied with and without TA. The TL glow curves are composed of mainly two broadbands located around room temperature (RT) at 127 °C and 127–400 °C. TA at higher temperatures produces a shift of the maximum TL peak toward the higher‐temperature side. After TA at 1000 °C, the TL repeatability is significantly improved with deviations around 3.4%, showing better TL performance. The TL fading in 24 h immediately after irradiation at RT is observed to be around 49–60% without TA and 18–26% after TA at 1000 °C. The present findings demonstrate that TA at 1000 °C increases the TL performance of the HPHT MD particles as TL dosimeters suitable for ionizing radiation.

Uncertainty of LiF thermoluminescence at low dose levels: Experimental results

The LiF:Mg,Ti (TLD-100) thermoluminescence (TL) detectors are widely used in many dosimetric applications, particularly in personal dosimetry area. In the present study, the uncertainty of TLD-100 measurements at the low dose levels has been assessed for different TL readout analysis methods. The criteria used to evaluate the minimum measurable dose (MMD) have been also investigated. It has been found that between-sample variations and the precision of the TL measurements were the significant uncertainty components. However, the precision of the measurement is critically dependent on the TL readout analysis and background (BG) subtraction methods. The estimation of the MMD based on the 3σBG approach may lead to inaccurate measurements. On the other hand, a new criterion for evaluating the MMD based on the signal-to-noise ratio and can be evaluated from the glow-curve deconvolution analysis has been established. It has been shown that the implementation of this criterion ensures acceptable levels for both the precision and trueness of TL measurements.

Internal Radiation Levels in Natural Quartz Crystals Collected from Southwestern Nigeria; Implications on Thermoluminescence Studies

The relationship between natural thermoluminescence (TL) signal, activity concentrations and the TL sensitivities of twelve (12) quartz samples from different origins were investigated in this study. Gamma spectrometry measurements on the samples were carried out with coaxial-type Germanium detectors (Canberra Industries Inc., Meriden, CT, USA). The TL measurements on the samples were measured using a RISØ TL/OSL reader (model TL/OSL–DA–15). Concentrations of radionuclide activities were only detected in three samples with very low values as compared with world’s average. The highest dose rate in one of the samples was observed to be a factor of 15 lesser than a case of self-dose reported in the literature. The three samples with detectable activity concentrations are the one that possess highest TL signals. All the samples with an exception of one exhibit dependence of sensitization factor of 110 °C TL glow-peak on the equivalent dose (ED). This observation suggested a correlation between the ED of quartz and the sensitization factor of its 110 °C TL peak, an indication of the importance of ED in quartz TL and Optically Stimulated Luminescence (OSL) characteristics. There was no possibility of self-dose effect in all the samples and their radiation safety in exploration and applications in electronics and gemology are validated.

Thermoluminescence characteristics of GaSe and Ga2Se3 single crystals

GaSe and Ga2Se3 are semiconducting compounds formed from same constituent elements. These compounds have been attractive due to their optoelectronic and photovoltaic applications. Defects take remarkable attention since they affect quality of semiconductor devices. In the present paper, deep defect centers in GaSe and Ga2Se3 single crystals grown by Bridgman method were reported from the analyses of thermoluminescence measurements performed in the 350–675 K range. Experimental TL curves of GaSe and Ga2Se3 single crystals presented one and two overlapped peaks, respectively. The applied curve fitting and initial rise techniques were in good agreement about trap activation energies of 0.83 eV for GaSe, 0.96 and 1.24 eV for Ga2Se3 crystals. Crystalline structural properties of the grown single crystals were also investigated by x-ray diffraction measurements. The peaks observed in XRD patterns of the GaSe and Ga2Se3 crystals were well-consistent with hexagonal and zinc blende structures, respectively.

Persistent luminescence ratiometric thermometry

Over the past twenty years, luminescence intensity ratio (LIR)-based temperature sensing technology has become a research hotspot. Despite the great progress in this field, the main limitation of conventional LIR thermometry is the requirement of continuous exposure to excitation source during measurement that may result in thermal effect and thus disturb the accuracy of temperature readout. In order to solve this problem, a new type of thermometry is proposed here, exploiting NaYF4:Er3+ that exhibits long persistent luminescence (PersL) over almost one day. The LIR between the two green PersL bands associated with the 2H11/2→4I15/2 and 4S3/2→4I15/2 electronic transition of Er3+ ions in NaYF4:Er3+ is demonstrated to be a reliable indicator of temperature, which could effectively avoid the long-term exposure to irradiation source. To clearly emphasize the difference between a regular LIR and this research, the newly proposed strategy here is named as persistent luminescence intensity ratio (PLIR) thermometry. The density functional theory and thermoluminescence measurement indicate the PersL mechanism of NaYF4:Er3+ probably stems from the fluorine vacancy related defects. The proposed PLIR thermometry, different from the traditional LIR counterpart, is believed to open a new road to determine temperature via an interesting and reliable way, which will greatly inspire other researchers in the related fields.

Photoluminescence and thermoluminescence properties of manganese doped BaAl2O4 phosphor

A novel rare-earth free green-emitting Mn doped BaAl2O4 nanophosphor was prepared by combustion method. The crystal structure, morphology, phosphorescence, thermoluminescence and chemical composition were investigated. The XRD patterns confirmed the hexagonal BaAl2O4 phase and the existence of a small fraction of BaAl12O19 impurity phase. The SEM studies revealed uneven morphology with both nano-rods and hexagonal sheets particles. PL measurements, excited at 428 nm, exhibited a 512 nm emission from the 4T1→6A1(6S) transition of Mn2+ ions and a very weak emission band at 685 nm from the 2Eg→4A2g transition of Mn4+ ions. The green emission at 512 nm was observed to have an average decay time of 4.88 ms. Thermoluminescence measurements showed a glow curve with at least one prominent peak around 114 °C, and two weak peaks at 186 °C and 292 °C. The kinetic analysis proved it to be of second order, with an average activation energy of 0.84 eV.