Luminescence and evaluation of trapping parameters in NaMgSO4Cl: X (X=Cu or Ce) phosphor

Thermoluminescence (TL) characteristics of recently developed high sensitive mixed halosulphate phosphors, NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce were studied in comparison with CaSO₄: Dy in order to assess the possibility of their use in personal monitoring and TLD phosphors at very low dose of 5 Gy. It was found that NaMgSO₄Cl: Cu is 5.59 times and NaMgSO₄Cl: Ce is 6.18 times more sensitive as compared to standard CaSO₄: Dy. UV photo-excited luminescence from Cu to Ce doped NaMgSO₄Cl halosulphate phosphors has been investigated. The intense emission of the spectrum is assigned to electronic transitions 3d⁹4s¹→3d¹⁰ in monovalent copper ion and 5d→4f in Ce³⁺ ions. Increase in PL peak intensity suggesting that Cu and Ce play an important role in PL emission in the present matrix. These phosphors were synthesized by the wet chemical method. XRD, photoluminescence (PL) and thermoluminescence (TL) characterization of phosphors has been reported in this paper. The preparation of an inexpensive and high sensitive NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce with TL glow peaks for different concentrations are observed between 160 and 195 °C and between 200 and 225 °C, respectively, exposed to gamma-rays of ⁶⁰Co for their thermoluminescence (TL) properties. The glow curves have been recorded at a heating rate of 2 K s^?1 and irradiated at a dose rate of 0.995 kGy h^?1 for 5 Gy. In present study the trapping parameters such as order of kinetics (b), activation energy (E) and frequency factors (s) have been calculated for the 195 and 200 °C glow peaks of NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce, respectively by using Chen's method. The paper discusses the luminescence of Cu⁺ and Ce³⁺ by simple method of incorporation in NaMgSO₄Cl host.     

Lu2O3:Tb,Hf storage phosphor

Lu₂O₃:Tb,Hf ceramics containing 0.1% of Tb and 0–1.5% of Hf were prepared in reducing atmosphere at 1700 °C and their thermoluminescence properties were systematically studied. For comparison Tb,Ca co-doped specimen was also fabricated and investigated. The Tb,Hf ceramics shows basically a single TL band located around 180 °C as found with heating rate of 15 °C/min. Ceramics singly doped with Tb show complex TL glow curves indicating the presence of traps of very different depths. On the other hand Tb,Ca co-doping is beneficial for the development of shallow traps with the main TL band around 70 °C. Hence, the aliovalent impurities, Ca²⁺ and Hf⁴⁺, strongly influenced the traps structure in Lu₂O₃:Tb ceramics, each of them in its own specific way. Isothermal decay of Lu₂O₃:Tb,Hf at 185 °C was recorded and its shape suggest that multiple hole trapping occurs in the Lu₂O₃:Tb,Hf ceramics. Due to the different traps depths the Lu₂O₃:Tb,Hf ceramics possess properties typical for storage phosphors, while Lu₂O₃:Tb,Ca is a persistent luminescent material rather.     

5D0→7F1 and 5D0→7F2 transition in europium doped halosulphates for mercury-free lamps

Polycrystalline Na₃SO₄F:Eu and NaMgSO₄F:Eu halosulphate phosphors prepared by a wet chemical method have been studied for its photoluminescence (PL) and thermoluminescence (TL) characteristics. Two well resolved peaks are observed at 593 nm and 614 nm, which are assigned to due to ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions of Eu³⁺ ions. TL is observed at temperatures between 100 °C and 300 °C. In this paper, we report PL emission spectra of Eu³⁺ and TL glow curves, which are more sensitive than the standard TLD-CaSO₄:Dy. The presented phosphors are applicable for the mercury free lamps and solid state lighting devices.     

Thermoluminescence,photoluminescence and EPR studies on Mn2+ activated yttrium aluminate (YAlO3) perovskite

Thermoluminescence (TL) measurements were carried out on undoped and Mn²⁺ doped (0.1 mol%) yttrium aluminate (YAlO₃) nanopowders using gamma irradiation in the dose range 1–5 kGy. These phosphors have been prepared at furnace temperatures as low as 400 °C by using the combustion route. Powder X-ray diffraction confirms the orthorhombic phase. SEM micrographs show that the powders are spherical in shape, porous with fused state and the size of the particles appeared to be in the range 50–150 nm. Electron Paramagnetic Resonance (EPR) studies reveal that Mn ions occupy the yttrium site and the valency of manganese remains as Mn²⁺. The photoluminescence spectrum shows a typical orange-to-red emission at 595 nm and suggests that Mn²⁺ ions are in strong crystalline environment. It is observed that TL intensity increases with gamma dose in both undoped and Mn doped samples. Four shouldered TL peaks at 126, 240, 288 and 350 °C along with relatively resolved glow peak at 180 °C were observed in undoped sample. However, the Mn doped samples show a shouldered peak at 115 °C along with two well defined peaks at ～215 and 275 °C. It is observed that TL glow peaks were shifted in Mn doped samples. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped, and Mn doped samples were determined at different gamma doses using the Chens glow peak shape method and the results are discussed in detail.     

Thermoluminescence response in gamma and UV irradiated Dy2O3 nanophosphor

Low temperature solution combustion method was employed to synthesize Dy₂O₃ nanophosphors using two different fuels (sugar and oxalyl dihydrazine (ODH)). Powder X-ray diffraction confirm pure cubic phase and the estimated particle size from Scherrer's method in sugar and ODH fuel was found to be 26 and 78 nm, respectively, and are in close agreement with those obtained using TEM and W–H plot analysis. SEM micrographs reveal porous, irregular shaped particles with large agglomeration in both the fuels. An optical band gap of 5.24 eV and 5.46 eV was observed for Dy₂O₃ for sugar and ODH fuels, respectively. The blueshift observed in sugar fuel is attributed to the particles size effect. Thermoluminescence (TL) response of cubic Dy₂O₃ nanophosphors prepared by both fuels was examined using gamma and UV radiations. The thermoluminescence of sugar used samples shows a single glow peak at 377 °C for 1–4 kGy gamma irradiations. When dose is increased to 5 kGy, two more shouldered peaks were observed at 245 and 310 °C. However, in TL of ODH used samples, a single glow peak at 376 °C was observed. It is observed that TL intensity is found to be more in sugar used samples. In UV irradiated samples a single glow peak at 365 °C was recorded in both the fuels with a little variation in TL intensity. The trapping parameters were estimated by different methods and the results are discussed.     

Mechanoluminescence,thermoluminescence and photoluminescence studies on Al2O3:Tb phosphors

Terbium activated Al₂O₃ phosphors were synthesized by combustion technique using hydrazine as a reductive non-carbonaceous fuel. X-ray diffraction (XRD) patterns of the samples were recorded to confirm the formation of the sample. Scanning electron microscope (SEM) images were taken to study the surface morphology of the sample. The photoluminescence (PL), thermoluminescence (TL) and mechanoluminescence (ML) properties of the γ-ray irradiated samples were studied. ML was excited impulsively by dropping a piston on the sample. In ML glow curves one peak with a shoulder was observed. ML intensity increases with activator concentration. Optimum ML was observed for the sample having 0.5 mol% of Tb ions. In the TL glow curve two distinct peaks, one around 222 °C and another around 280 °C, were observed for the samples having 0.5 mol% of activator concentration. In the PL spectra the ⁵D₄→⁷F₅ line at 544 nm in the green region is observed, which is the strongest in Al₂O₃ system. It is suggested that de-trapping of trapped charge carriers followed by recombination is responsible for ML and TL in this system.     

TL and OSL studies on lithium borate single crystals doped with Cu and Ag

Lithium borate (LBO) single crystals doped with Cu and Ag (0.25 mol% each) (Li₂B₄O₇:Cu,Ag) are grown by the Czochralski method. The thermoluminescence readout on Li₂B₄O₇:Cu,Ag crystals showed three glow peaks at～375, 441 and 516 K for the heating rate of 1  K/s. The thermoluminescence sensitivity of the grown Li₂B₄O₇:Cu,Ag single crystals is found to be 5 times TLD-100 and a linear dose response in the range 1 mGy to 1 kGy. The glow curve deconvolution reveals nearly first order kinetics for all the three peaks with trap depths 0.77, 1.25 and 1.34 eV respectively and corresponding frequency factors 1.6×10⁹, 1.3×10¹³ and 6.8×10¹¹ s^?1. The continuous wave optically stimulated luminescence (CW-OSL) measurements were performed on the LBO:Cu,Ag single crystals using blue light stimulation. The traps responsible for the three thermoluminescence peaks in Li₂B₄O₇:Cu,Ag are found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response is established. The photoluminescence studies show that in case of co-doping of Ag in LBO:Cu the emission at 370 nm in Cu states dominates over the transitions in Ag states implying doping of Ag plays a role as sensitizer when co-doped with Cu and increases overall emission.     

Thermally assisted OSL from deep traps in Al2O3:C

The present work suggests an alternative experimental method in order to not only measure the signal of the deep traps in Al₂O₃:C without heating the sample to temperatures greater than 500 °C, but also use this signal for high dose level dosimetry purposes as well. This method consists of photo transfer OSL measurements performed at elevated temperatures using the blue LEDs (470 nm, FWHM 20 nm) housed at commercial Risø TL/OSL systems, after the sample was previously heated up to 500 °C in order to empty its main TL dosimetric trap. The influence of this procedure on specific features such as glow curve shape and sensitivity of the main TL glow peak was also studied.     

Thermoluminescence response of the larimar rocks

The aim of this paper is to evaluate the thermoluminescent (TL) response of a larimar, a variety of pectolite (NaCa₂Si₃O₈[OH]). It is a blue pectolite only found on the terrestrial crust of the province of Barahona, in the south-western region of the Dominican Republic. The larimar rock used in this study, presented a light-blue color with brown areas. X-ray powder diffractometry (XRD), showed that the light-blue portion of the rock is composed essentially by pectolite and the brown portion is composed by a mixture of minerals. Aliquots of 5 mg of light-blue portions were irradiated with gamma rays with doses from 10 to 10⁴ Gy and the TL glow curves were obtained from 50 to 400 °C. The glow curve showed a broad peak around 150 °C and a peak near 280 °C. Different pre-heat condition were used to remove the broad peak. The TL emission of the main peak appeared in the region of 580 nm. The TL response of the main peak showed a linear behavior up to 2500 Gy and a sub-linear behavior above this dose value. Studies of the 30 day fading effects in TL signal using a pre-heating temperature around 180 °C during 15 min were carried out and fading near 25% was observed.     

Synthesis,characterisation, luminescence and defect centres in solution combustion synthesised CaZrO3:Tb3+ phosphor

Tb³⁺ doped CaZrO₃ has been prepared by an easy solution combustion synthesis method. The combustion derived powder was investigated by X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy techniques. A room temperature photoluminescence study showed that the phosphors can be efficiently excited by 251 nm light with a weak emission in the blue and orange region and a strong emission in green light region. CaZrO₃:Tb³⁺ exhibits three thermoluminescence (TL) glow peaks at 126 °C, 200 °C and 480 °C. Electron Spin Resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the centres responsible for the TL peaks. The room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0233 is identified as an O^? ion. Centre II with an axial symmetric g-tensor with principal values g_=1.9986 and g_?=2.0023 is assigned to an F⁺ centre (singly ionised oxygen vacancy). An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F⁺ centre) seems to originate from an F centre (oxygen vacancy with two electrons). The F centre and also the F⁺ centre appear to correlate with the observed high temperature TL peak in CaZrO₃:Tb³⁺ phosphor.     

Luminescence and defect studies of YAlO3:Dy3+, Sm3+ single crystals exposed to 100 MeV Si7+ ion beam

Ionoluminescence (IL) and photoluminescence (PL) spectra for different rare earth ions (Sm³⁺ and Dy³⁺) activated YAlO₃ single crystals have been induced with 100 MeV Si⁷⁺ ions with fluence of 7.81×10¹² ions cm^?2. Prominent IL and PL emission peaks in the range 550–725 nm in Sm³⁺ and 482–574 nm in Dy³⁺ were recorded. Variation of IL intensity in Dy³⁺ doped YAlO₃ single crystals was studied in the fluence range 7.81×10¹²–11.71×10¹² ions cm^?2. IL intensity is found to be high in lower ion fluences and it decreases with increase in ion fluence due to thermal quenching as a result of an increase in the sample temperature caused by ion beam irradiation. Thermoluminescence (TL) spectra were recorded for fluence of 5.2×10¹² ions cm^?2 on pure and doped crystals at a warming rate of 5 °C s^?1 at room temperature. Pure crystals show two glow peaks at 232 (Tg₁) and 328 °C (Tg₂). However, in Sm³⁺ doped crystals three glow peaks at 278 (Tg₁), 332 (Tg₂) and 384 °C (Tg₃) and two glow peaks at 278 (Tg₁) and 331 °C (Tg₂) in Dy³⁺ was recorded. The kinetic parameters (E, b s) were estimated using glow peak shape method. The decay of IL intensity was explained by excitation spike model.     

Radiation-induced thermoluminescence characteristics of feldspar upon different heat and microwave treatments

Feldspar minerals are well-known markers for thermoluminescence (TL)-based identification of irradiated foodstuff because of their high TL sensitivity and characteristic TL glow curves. Post-irradiation processing, particularly heating, may affect luminescence properties. In the present study, the effect of boiling, roasting, and microwave treatments on TL properties of irradiated (0, 5, and 10 kGy) feldspar was investigated. The TL glow peak faded (TL peak maxima shift towards higher temperature) upon boiling or roasting, which was mainly dependent upon treatment temperature and time. This effect was most apparent in the roasted samples. Liquid samples showed more changes in TL characteristics than solid samples upon microwave treatment; however, the effect was less prominent compared to those of roasting and boiling. TL ratios could not confirm the TL results when boiled and roasted samples were treated at ≥100 °C, whereas the microwave treatment showed a negligible effect on the TL ratio.     

Thermo,Iono and photoluminescence properties of 100 MeV Si7+ ions bombarded CaSiO3:Eu3+ nanophosphor

This paper reports on the thermo (TL), iono (IL) and photoluminescence (PL) properties of nanocrystalline CaSiO₃:Eu³⁺ (1–5 mol %) bombarded with 100 MeV Si⁷⁺ ions for the first time. The effect of different dopant concentrations and influence of ion fluence has been discussed. The characteristic emission peaks ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions was recorded in both PL (1×10¹¹–1×10¹³ ions cm^?2) and IL (4.16×10¹²–6.77×10¹² ions cm^?2) spectra. It is observed that PL intensity increases with ion fluence, whereas in IL the peaks intensity increases up to fluence 5.20×10¹² ions cm^?2, then it decreases. A well resolved TL glow peak at ～304 °C was recorded in all the ion bombarded samples at a warming rate of 5 °C s^?1. The TL intensity is found to be maximum at 5 mol% Eu³⁺ concentration. Further, TL intensity increases sub linearly with shifting of glow peak towards lower temperature with ion fluence.     

Effect of Eu and Pb doping on the dosimetric properties of LiCAF

LiCaAlF₆ (LiCAF) crystals doped with two different ions (europium and lead) have been investigated as potential new dosimetric materials. The stability of thermally stimulated luminescence (TSL) glow peaks in LiCAF:Eu was evaluated by means of the initial rise technique. The decay times at room temperature of the traps related to the dosimetric glow peaks were found to range between 40 and 2 × 10⁴ years confirming the good dosimetric characteristics of this crystal. The glow curve of LiCAF:Pb is dominated by a peak at approximately 300 °C emitting in the UV region (³P_0,1–¹S₀ transition of Pb²⁺) superimposed to a very broad structure at lower temperature (20–200 °C) featuring recombination at an intrinsic defect centre. The anomalous behavior of the low temperature structure during thermal cleaning procedures prevented any reliable numerical analysis of the TSL glow peak at 300 °C.     

Thermoluminescence characterization of the Cu(Tb,Tm)-12CaO-7AL2O3 compounds obtained by combustion synthesis

The thermoluminescence (TL) properties of dode-calcium hepta-aluminate (Ca₁₂Al₁₄O₃₃) enabled by 12CaO-7Al₂O₃ doped with rare earth and transitions metals ions have been studied and their suitability for radiation dosimetry applications is discussed. It was observed that this calcium aluminate phase doped with Tm-Cu at concentration of 0.1 mol% is a good candidate for dosimetric applications since it presents well-defined single peak observed at 240 °C and 320 °C and a linear response to gamma radiation dose from 5 × 10⁻³ Gy up to 100 Gy.     

Oxygen adsorption properties of YBaCo4O7-type compounds

The oxygen adsorption and desorption of newly found compounds RBaCo₄O₇ (R = Y, Dy–Lu, In) were investigated by thermogravimetry (TG) in the temperature range from room temperature to 1100 °C. The influence of Co replaced by Zn and Fe on the oxygen diffusion properties of YBaCo₄O₇ was also studied. TG results showed clearly that all RBaCo₄O₇ compounds basically experience two oxygen adsorption and desorption processes in the temperature range 20∼1100 °C in oxygen flow. One happens at about 200∼450 °C and the another happens at about 660∼1050 °C. The differences between the resulting states by adsorbing oxygen at lower and high temperature were discussed based on the X-ray diffraction (XRD) patterns and TG data. We showed evidence that the oxygen adsorption at the lower temperature has a small activation energy, while the oxygen adsorption at the higher temperature has a large activation energy. The oxygen adsorbed at high temperature will destroy the RBaCo₄O₇ structure. Zn substituting in the YBaCo_4 − xZn_xO₇ influences the oxygen diffusion behavior prominently, the amount of oxygen adsorbed becomes increasingly weak with the increase of Zn content and disappears completely for the samples with x ≥ 2.0. However, replacement of Co by Fe has little effect on the oxygen absorption process.     

Segments of a commercial Ge-doped optical fiber as a thermoluminescent dosimeter in radiotherapy

Optical fibers have been proposed as dosimeters in both diagnostic and radiotherapy applications. A commercial germanium (Ge)-doped silica fiber with a 50 μm core diameter which showed good thermoluminescence (TL) properties was selected for this study. The radiation sources used were a high dose rate brachytherapy iridium-192, MV photon and MeV electron beams from a linear accelerator. The coating of the fiber was chemically removed and then annealed at 400 °C for 1 h prior to irradiation. After irradiation, the fiber was read on a Harshaw Model 3500 TLD reader. The optical fiber had one well-defined glow peak at 327 ± 2 °C at all the radiotherapy energies. The dose response was linear within the clinical relevant dose for all these energies. Reproducibility was mainly within 4–6% (one standard deviation) for high energy photons and electrons. The fiber was found to be energy independent within the MV photon energy range. At room temperature the fading up until 1 month was around 6% which was within the 6% uncertainty of the sensitivity calibration of the fiber. Re-using the fiber four times did not significantly alter the sensitivity factor. The optical fiber was found to be dose rate as well as angular independent. Central axis depth dose curves of both 10 MV photons and 12 MeV electrons using the fiber showed relatively good agreement to standard depth dose curves in water within 4%. The Ge-doped fiber is a promising TL dosimeter but improvements have to be made to reduce the reproducibility within 3% for high energy photons and electrons.     

Effects of doping with nanoscale Co3O4 particles on the superconducting properties of powder-in-tube processed MgB2 tapes

Nanoscale Co₃O₄ particles were doped into MgB₂ tapes with the aim of developing superconducting wires with high-current-carrying capacity. Fe-sheathed MgB₂ tapes with a mono-core were prepared using the in situ powder-in-tube (PIT) process with the addition of 0.2–1.0 mol% Co₃O₄. The critical temperature decreased monotonically with an increasing amount of doped Co₃O₄ particles for all heat-treatment temperatures from 600 to 900 °C. However, the transport critical current density (J_c) at 4.2 K varied with the heat-treatment temperatures. The J_c values in magnetic fields ranging from 7 to 12 T decreased monotonically with increasing Co₃O₄ doping level for a heat-treatment temperature of 600 °C. In contrast, some improvements on the J_c values of the Co₃O₄ doped tapes were observed in the magnetic fields below 10 T for 700 and 800 °C. Furthermore, J_c values in all the fields measured increased as the Co₃O₄ doping level increase from 0 to 1 mol% for 900 °C. This heat-treatment temperature dependence of the J_c values could be explained in terms of the heat-treatment temperature dependence of the irreversibility field with Co₃O₄ doping.     

Thermoluminescence,infrared reflectivity and electron paramagnetic resonance properties of hemimorphite

Silicate mineral hemimorphite has been investigated concerning its TL, IR and EPR properties. A broad TL peak around 180 °C and a weaker and narrower peak around 360 °C were found in a sample annealed at 600 °C for 1 h and then irradiated. The deconvolution using the CGCD method revealed peaks around 132, 169, 222 and 367 °C. The reflectivity measurements showed several bands in the NIR region due to H₂O, OH and Al–OH complexes. No band was observed in the visible region. The thermal treatments were carried out from ∼110 to 940 °C and dehydration was observed, first causing a diminishing optical absorption in general and the disappearance of water and hydroxyl absorption bands. The EPR spectrum of natural hemimorphite, presented Cu²⁺ signals at g = 2.4 and g = 2.1 plus E₁′ signal superposed to Fe³⁺ signal around g = 2.0.     

Feasibility study of CaSO4:Eu,CaSO4:Eu,Ag and CaSO4:Eu,Ag(NP) as thermoluminescent dosimeters

This work evaluates the dosimetric properties of crystals of CaSO₄ doped with unusual elements, such as europium (Eu) and silver (Ag), including their nanoparticle forms, after the incorporation of glass or Teflon and compares them with well-known thermoluminescent dosimeters (TLD). X-ray diffraction analyses showed that samples of doped CaSO₄ exhibit only a single phase corresponding to the crystal structure of anhydrite. Optical spectroscopy confirmed the presence of Eu³⁺ in the crystal matrix and a luminescent gain due the presence of silver nanoparticles. The composites showed thermoluminescent emission glow curves, with a single peak centered at approximately 200 °C for pellets with Teflon and at 230 °C for pellets with glass. The dosimeters based on calcium sulfate doped with europium and silver nanoparticles provided the most intense thermoluminescent (TL) emission of the composites studied. In comparison with commercial TLD, such as LiF:Mg,Ti and CaSO₄:Dy, the CaSO₄:Eu,Ag(NP)+glass produced in this work presented similar low detection limits and higher sensitivity. The new methods for the preparation of dosimeters and the incorporation of glass are shown to be viable because all of the samples presented a linear, reproducible and first order kinetic TL emission.