Low Temperature TL Research Articles

Thermoluminescence characteristics of UV-irradiated natural hackmanite

Hackmanite has received extensive attention from scholars in recent years. However, there is still no report on the thermoluminescence properties of natural hackmanites under UV irradiation, as well as its relative electron trap and luminescence center. In this paper, the structural defects and thermoluminescence spectroscopic properties of hackmanite are comprehensively characterized by XRD, TL spectroscopy, SEM, EPR, XPS and Raman spectroscopy. The traps depth of TL peaks are calculated by computerized glow curve deconvolution (CGCD) techniques. And the charge transition energy levels of intrinsic defects in Na8Al6Si6O24(Cl,S)2 are calculated by spin-polarized density-functional theory (DFT) in VASP. It shows that the low-temperature TL peaks of hackmanite are associated with Cl vacancies and photochromic properties. The high-temperature peak is caused by marginal oxygen vacancies. The results are conducive to deepening the understanding of structural defects of the hackmanites and linking the thermoluminescence with the phototropy.

Optical properties of pure and Sn-doped β-Ga2O3 single crystals grown by optical float zone technique

High-quality single crystals of both pure and Sn:β-Ga2O3 single crystals weregrown using the optical floating zone technique and a comprehensive study of its luminescence and scintillation properties was carried out. The pure and Sn:β-Ga2O3 grown crystals were oriented along (100) by Laue diffraction pattern and its monoclinic structure was confirmed using a single crystal XRD. X-ray induced luminescence spectrum shows a maximum emission peak at 365 nm. The cut off wavelength was observed around 258 nm and the optical band gap was calculated to be 4.64 eV from UV–Vis-NIR transmission spectroscopy. The room temperature Raman spectra were recorded and the various vibration modes were investigated. Low temperature (10 to 300 K) and high temperature (325 to 675 K) TL measurements were carried out on X-ray irradiated crystals and its TL kinetic parameters such as activation energy (eV) and frequency factor (S) were calculated. Scintillation decay time profiles were measured for both pure and Sn-doped crystals under 137Cs γ-ray excitation. The calculated scintillation light output is 2300 Ph/5.5 Mev for Sn:β-Ga2O3 crystal under α-particle excitation from 241Am radiation source.

Magnetocaloric response with significant mechanical efficiency in frustrated intermetallic compound Pr2Co0.86Si2.88

Magnetically frustrated materials are considered as a promising unconventional members of caloric materials. Here, the magnetocaloric properties of the frustrated Pr2Co0.86Si2.88 have been investigated and discussed with the aid of density functional theory (DFT) calculations. The material exhibits a magnetic entropy change (−ΔSM) of 13.1 J/kg-K for ΔH = 70 kOe around low-temperature transition TL ∼ 4 K associated with the antiferromagnetic coupling between localized Pr-4f and itinerant Co-3d moments. Despite the absence of any long-range magnetic order, the obtained − ΔSM is one of the highest among the known Pr-based good magnetocaloric materials at cryogenic temperature range. It also exhibits a relative cooling power (RCP) of ∼ 201 J/kg and an adiabatic temperature change of 6.3 K around TL at 70 kOe. Moreover, the compound also exhibits a high mechanical efficiency and moderate electrical efficiency, being beneficial for possible technological applications.

Size-Dependent Persistent Luminescence of YAGG:Cr3+ Nanophosphors.

In the current work, YAGG:Cr3+ nanophosphors were synthesized by the Pechini method and then annealed at different temperatures in the range 800–1300 °C. The structure and morphology of the samples were characterized by X-ray Powder Diffraction (XRPD). The lattice parameters and average crystalline sizes as site occupation by Al3+ and Ga3+ ions were calculated from the Rietveld refinement data. To investigate the effect of crystalline size of the materials on their optical properties: excitation and emission spectra were recorded and analyzed. Finally, the effect of crystalline size on the probability of carrier recombination leading to PersL was determined experimentally with thermoluminescence analyses. The Tmax-Tstop method was applied to determine the trap type and particle size (calcination temperature) effect on their redistribution. A correlation between structural changes and trap redistribution was found. In particular, the extinction of high-temperature TL maximum with increasing annealing temperatures is observed, while low-temperature TL maximum increases and reaches a maximum when the lattice parameter reaches saturation.

Recombination pathways in a BeO yielding two main dosimetric TL peaks

Apart from the commercially used Thermalox, BeOR is a new type of Beryllium Oxide fabricated by a different company in Turkey. As it is shown by other groups, this dosimeter yields two overlapping main dosimetric TL peaks in the temperature region of 100–300 °C and one peak at 350 °C. The aim of the present study is the calculation of the activation energies of these two peaks with the use of specific protocols, including the Fractional Glow Technique (FGT), an Isothermal Decay signal (PID) and the Peak Shape Methods (PSM). Also, these experimental procedures were conducted in two different readers, namely the Harshaw and the Risø reader, for better repeatability and in order to minimize the error of the calculations. Moreover, another goal is to correlate the activation energy values with the recombination pathways that are present in the BeOR and its corresponding peaks. Specifically, both peaks have activation energies around 1–1.3 eV in most cases, although there are some kinds of indications for a difference in the pathways, as the high-temperature region TL main peak seems to follow the localized recombination via tunneling, in contrast with the low-temperature region TL main peak which sticks to the delocalized model with the passing via the conduction band.

Numerical study of natural convection of nanofluids in an inclined flat bottom flask using finite-volume approach.

In this work, we study numerically the natural convection of nanofluids (NF) in an inclined flat bottom flask; it is one of laboratory flasks used in organic chemistry synthesis. The main reason of this study is to enhance the thermal properties of the reaction medium inside the flat bottom flask and to ameliorate the rate of chemical reactions using nanofluids. The flat bottom wall is maintained at a constant high temperature Th. While the top, left and right walls of the cavity are maintained at a low temperature TL. The NF comprises Cu and Al2O3 nanoparticles (NP) suspended in pure water. The governing equations are solved numerically using the finite-volume approach and formulated using the Boussinesq approximation. In this simulation we examined the effects of the NP volume fraction (φ) from 0% to 5%, the Rayleigh number from 103 to 106, the various inclination angles of enclosure (γ=0°,5°,10°, 15°) and the NF type (Cu and Al2O3) on the flow streamlines, isotherm distribution and Nusselt number. The obtained results show that the addition of Cu and Al2O3 NP increases the mean Nusselt number which enhances the heat transfer in the flat bottom flask and causes significant changes in the flow pattern. In addition, the mean Nusselt number is increase with increasing the Rayleigh number and the volume fraction and the best results have obtained from the Cu nanofluide. Also, as the inclination angle increases the mean Nusselt number decreases and the highest value of Nusselt number was obtained for a vertical enclosure (γ=0°). The obtained streamlines are mostly symmetric and their values are generally increase by increasing the Rayleigh number and volume fractions of NPs. Besides, the obtained isotherms are generally follow the geometry of the flat bottom flask.

Solar-to-work conversion from meteorological data

The aim of this paper is to develop an algorithm able of determining the exergy or maximum work (GHIX) that can be extracted from solar global horizontal irradiance (GHI). A theoretical device made of a radiation absorber-emitter slab, connected to a temperature Ta heat reservoir, to a work extractor that operates in connection with a low temperature TL = Tamb heat reservoir, is exposed to an annual typical meteorological sun, made-up of hourly data, from five cities in Uruguay. The slab to be impinged by GHI has to be heated to the optimum high temperature Ta, so to become the hot reservoir for the thermal cyclic motor that will produce maximum work GHIX. Two alternative procedures are being used in making the year's hourly optimum Ta series; maximize the work production or minimize the entropy production, equivalent to minimize the exergy annihilation. Exergy factor GHIX/GHI results in a weak logarithmic function of GHI and in a weak geo-reference-dependence, for Uruguay. Annual exergy factor in all five cities in Uruguay belong to the interval (0.814<GHIX/GHI<0.819) with average (0.816). Agreement exists with similar measurements from other places found in the literature.

Effective temperature and performance characteristics of heat engines

For a heat engine working between two heat reservoirs, a hot reservoir at high temperature TH and a cold reservoir at low temperature TL, an effective temperature and an effective efficiency are introduced. The effective temperature is defined as the square root of the ratio between the net work output of the heat engine wnet and the SOT function (a new function introduced in this article). The SOT function is defined as the negative of the cyclic integral of the heat transfer change divided by the square of the temperature. The effective efficiency of the heat engine is defined (a novel definition) as one minus the ratio between the low temperature and the effective temperature. The effective temperature and the effective efficiency are worked out in details for the Carnot heat engine and the air standard cycles (Otto, Brayton, Stirling, and Ericsson). It was found for the considered cycles that the effective temperature is given by the expression () and the effective efficiency is given by the expression () for all the considered cycles. The importance of these two proposed measures is twofold: educational and they could be used as a quick tool by the designer.

An alternative method for immediate dose estimation using CaSO4:Dy based TLD badges

CaSO4:Dy based Thermoluminescence dosimeters (TLDs) are being used in country wide personnel monitoring program in India. The TL glow curve of CaSO4:Dy consists of a dosimetric peak at 220°C and a low temperature peak at 120°C which is unstable at room temperature. The TL integral counts in CaSO4:Dy reduces by 15% in seven days after irradiation due to the thermal fading of 120°C TL peak. As the dosimetric procedure involves total integrated counts for dose conversion, the dosimeters are typically read about a week after receiving. However in the event of a suspected over exposure, where urgent processing is expected, this poses limitation. Post irradiation annealing treatment is used in such cases of immediate readout of cards. In this paper we report a new and easier to use technique based on optical bleaching for the urgent processing of TLD cards. Optical bleaching with green LED (∼555nm photons) of 25,000lux for one and half hour removes the low temperature TL peak without affecting the dosimetric peak. This method can be used for immediate dose estimation using CaSO4:Dy based TLD badges.

Post-IR IRSL production in perthitic feldspar

A museum sample of perthitic feldspar was used to study the production of post-IR IRSL signals. It was found that traps responsible for low temperature (∼230 °C) TL peaks play an unexpectedly important role in post-IR IRSL production. During the production of the IRSL signal during low temperature IR stimulation (100 °C), electrons are optically transferred from IRSL traps into these TL traps which have been emptied by the preceding preheat at 320 °C. Subsequent heating to 300 °C causes thermal transfer of these electrons from these traps back into previously emptied IRSL traps which are related to the high temperature TL peaks. IR stimulation of these electrons results in post-IR IRSL. Thus the initial source of the post-IR IRSL signal is the same as the IRSL signal, with a role being played by intermediate traps that give rise to TL signals between 200 and 250 °C, and the final source is similar to that of the IRSL signal. Therefore the post-IR IRSL signal is a by-product of the production of the IRSL signal. It was also found that post-IR IRSL production with high post-IR IR stimulation temperatures (e.g. >230 °C) additionally includes a small contribution from the post-IR isothermal decay of high temperature TL peaks that are not sensitive to IR stimulation at low stimulation temperatures.

Comparison of the properties of various optically stimulated luminescence signals from potassium feldspar

Abstract Various optically stimulated luminescence signals from K-feldspar have been used to determine the equivalent doses of sediment samples. Understanding the properties of these optical signals is critical to evaluate their applicability and limitations to optical dating. In this paper, some properties of IRSL, post-IR OSL and post-IR IRSL signals (detected in the UV region using U-340 filters) from a museum sample of K-feldspar were investigated by analyzing the relationships between optical and TL signals, and the effect of optical bleaching and heating on optical signals. The trap parameters of the different optical signals were calculated using the pulse annealing method. The results show that this sample exhibits two regenerated TL peaks at ∼140 and ∼330 °C. Corresponding to the low temperature TL peak, the OSL and post-IR OSL signals appear to be more associated with lower temperature TL than the IRSL signal measured at 50 °C. Corresponding to the high temperature TL peak, the post-IR IRSL signals mainly originate from the more thermally stable traps associated with the high temperature TL, compared with the IRSL and post-IR OSL signals. However, the post-IR IRSL225 °C signal is shown to be hard to be bleached by blue light and simulated sunlight, compared with the IRSL50 °C and low temperature post-IR IRSL signals. The implication for optical dating is that the elevated temperature post-IR IRSL signals can be preferentially applied over other signals from K-feldspar, but it is desirable that the effectiveness of the pre-depositional zeroing of these signals is assessed.

Chemical pressure, dilution and disorder in the heavy fermion compoundsCe3 − xLaxPd20Si6 ()

The heavy fermion compound Ce3Pd20Si6 is one of the rare examples of a cubic system with a readily accessible quantumcritical point. Ce atoms at the two different sites 4a and 8c of the crystalstructure have recently been shown to have different crystal field ground states (Γ7 andΓ8,respectively) and are assumed to be responsible for the two different low-temperature phase transitionsat TL and TU, which have been tentatively attributed to antiferromagnetic and antiferroquadrupolarorder, respectively. Here we present electrical resistivity measurements in a widetemperature range (50 mK–300 K) on two new representatives of the La substitution seriesCe3 − xLaxPd20Si6, and . Put in the context of previously published data our results indicate that La preferentiallyoccupies the 4a site and that Ce ions at the 8c site have a sizably larger Kondotemperature. Low-temperature resistivity measurements in applied magnetic fieldssuggest that (disorder smeared) quantum critical points exist in the and samples at fields below 1 T.

Low temperature TL studies on indigenously developed and commercial α-AL 2 O 3 :C

Low temperature TL studies on indigenously developed and commercial α-AL ₂ O ₃ :C

Reddish orange long lasting phosphorescence of Sm 3+ in Sr 2ZnSi 2O 7:Sm 3+ phosphors

Long lasting phosphorescence phosphors with composition of (Sr 1- x Sm x) 2ZnSi 2O 7 were prepared by conventional high-temperature solid-state method. Their properties were systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence spectra. The results showed that these phosphors emitted reddish orange light that corresponds to the characteristic emission due to the 4G 5/2→ 6H 5/2, 6H 7/2 and 6H 9/2 transitions of Sm 3+. After the UV light excitation source was switched off, the bright reddish orange long lasting phosphorescence could be observed and it could last for about 30 min in the limit of light perception of dark-adapted human eyes (0.32 mcd/m 2). A wide TL band raging from room temperature to 700 K with two dominating peaks at 340 and 602 K appeared in the TL spectrum. The TL curve could be fitted to five TL peaks and the low temperature TL peak at 340 K was found to be responsible for the long lasting phosphorescence. Also, the mechanism was discussed.

Physiological optimality, allocation trade-offs and antioxidant protection linked to better leaf yield performance in drought exposed mulberry

Mulberry (Morus spp. L.), usually linked to silkworm rearing, is now considered as a potential forage for livestock feeding and has great potential in world agriculture. Trait-based investigations for leaf yield stability in mulberry under water stress have not been studied extensively. The present study aims to identify candidate traits conferring leaf yield stability in mulberry under drought. Four popular, indigenous mulberry cultivars (Morus indica L. cvs AR-12, K-2, M. Local and V-1) were investigated. Low leaf temperature (T(l)), higher internal/ambient CO(2) ratios (C(i)/C(a)), greater stomatal conductance to CO(2) (g(s)) and stability in photosystem II efficiency were associated with better net photosynthetic rates (P(n)) in V-1, generating maximum leaf yield when compared to other drought-exposed cultivars. Increased accumulation of foliar α-tocopherol and ascorbic acid-glutathione pool, associated with higher carotenoids, proline and glycine betaine, facilitated lower lipid peroxidation and better leaf yield in V-1 under drought. Minimal plasticity in photosynthetic gas exchange traits and better quantitative growth characteristics were attributed to leaf yield stability under drought. Lower photoinhibition, stabilized photochemistry, effective osmoregulation and enhanced activity of foliar antioxidants extensively contributed to drought tolerance and higher leaf yield in mulberry.

Comparison between the low temperature thermoluminescence spectra in annealed LiF:Mg,Cu, LiF:Mg,Cu,P and LiF:Mg,Cu,Si

Two strong thermal peaks in the wavelength range 220–420nm have been detected at 128 and 140K in LiF:Mg,Cu, at 123 and 135K in LiF:Mg,Cu,P and at 125 and 133K in LiF:Mg,Cu,Si, respectively. The origin of these main TL peaks is discussed in terms of defect perturbed H–F and VK–e type recombination, respectively. The relative intensity between the two peaks in each sample and the emission spectra are dependent on the dopants.Annealing at 240–390°C can modify the low temperature TL features, especially in those samples doped with three impurities. The low temperature data give some clues to select most favourable dopants for future LiF-type dosimeters.

Spectral study on feldspar thermoluminescence process

Feldspar thermoluminescence fading phenomena were investigated here by using newly-constructed thermoluminescence spectrometer on the basis of charge-coupled detector, and thereafter the discussion and explanation on feldspar TL fading mechanism were presented. The experimental results show that the fading rate of feldspar TL depends on both wavelength and stimulated temperature, and normally the feldspar TL in every region of wavelength and temperature shows different traits, namely the low temperature TL (170°–190°) fading at the rate of logarithmic function and furthermore the TL of different wavelengths fading at approximately the same rate on the condition of 160° preheating. While the medium and high temperature TLs (290°–400°) do not show much thermal fading, their fading rate at room temperature invariably correlates well with their wavelength, namely the longer TL wavelength, the slower TL fading rate. The thermal instability of traps and the quantum-mechanical tunneling effects can explain the above fading phenomena respectively. It is recognized that feldspar TL fading depends on its wavelength, and furthermore new aspects of the solid thermoluminescence process can be displayed by the combination of three-dimensional TL spectral analysis and thermal fading or anomalous fading of TL for feldspar.

Low temperature thermoluminescence of annealed LiF:Mg, Cu, P

Two main thermoluminescence peaks at 123 and 135K, plus some weaker features near 65, 95, 242 and 265K, have been observed in LiF:Mg, Cu, P dosimeter samples that had been annealed at 240°C. The photon wavelengths in the main peaks span the spectral range from 250 to 470nm and the maximum intensity is near 310nm. The origin of these main TL peaks at 123 and 135K are discussed in terms of a range of defect complexes linked to intrinsic defects. In particular the temperatures match the annealing stages for defect perturbed F–H and VK–e type recombination, respectively. The 65K feature is considered as the result of electron–hole recombination via relaxed exciton decay. These models suggest reasons for the differences between the various emission bands and the longer wavelength emission linked to high temperature electron decay processes.High temperature annealing modifies the component low temperature TL features with annealing up to ∼300°C resulting in low temperature TL signal loss, but with partial recovery found for all the low temperature TL peaks when the samples were annealed at higher temperatures up to 390°C. It is suggested that the intensity loss and the recovery are the summation of numerous effects from a wide range of defect complex variations which exist in these heavily doped materials. The low temperature data offer further insights into the changes which occur in the structures related to optimising the high temperature TL dosimetry.

Effects of the ion-implantation on the thermoluminescence spectra of strontium titanate

Thermoluminescence of strontium titanate at low temperature is characterised by long wavelength emission centred near 800nm which contains at least three overlapping luminescence bands. The thermoluminescence is excited by X-ray irradiation at 25K of an entire sample. Room temperature ion-implantation into the surface layer changes the low temperature TL signals both in terms of their relative intensities and peak temperatures, as well as modifying the emission spectra. Such an intense perturbation of the bulk signals resulting from surface ion beam implantation is extremely unusual. However, it is well documented that for strontium titanate there are a variety of low temperature relaxations of the structure, and even phase transitions, which are highly sensitive to the presence of intrinsic defects, impurities and stresses.The ion-implantation damage in the surface is thus thought to act as a stress nucleation zone from which such relaxations can propagate throughout the entire crystal. There are consequent changes in the thermoluminescence in terms of defect stability and glow peak temperature. Details of such changes and modifications of emission spectra are reported.

Thermoluminescence spectra of rare earth doped Ca, Sr and Bafluorides

The low temperature TL spectra of undoped alkaline earth fluoridesconsistently show a continuous broad band emission around 280-300 nm. Theorigin of this emission is related to the relaxation of the self-trappedexciton (STE) in the form of an F-H pair. In doped samples, the broademission is quenched in favour of emissions from the rare earth (RE) impuritysites. The degree of quenching varies between the REs. The spectralmeasurements showed that the temperature of the glow peaks below roomtemperature is to a large extent independent of the RE impurity, although someeffects are related to the concentration. Additionally, the host material hasminimal effect on the glow peak temperatures, Tmax. The scale of theobserved differences in Tmax between the three hosts is similar to thedifferences in annealing temperatures of the Vk and H centres inthese hosts. Above room temperature, the glow peaks are specific to the addedRE ions and do not show common peaks.