Thermoluminescence properties of rare earth doped lithium magnesium borate phosphors

This paper reports the thermoluminescence (TL) properties of rare earth doped lithium magnesium borate (LMB) polycrystalline phosphor. LMB phosphor has been prepared by high temperature solid state diffusion method. Among all the rare earth doped LMB phosphors, terbium doped material has shown maximum TL sensitivity with a broad dosimetric glow peak at 240 °C. near the tissue equivalent TL phosphor with terbium dopant has about four times the TL sensitivity of TLD-100. The main dosimetric properties such as glow curve stability, TL response versus absorbed dose, post-irradiation storage stability, and reusability are investigated. This TL material has a linear dose response up to 10³ Gy, negligible storage fading and a simple annealing procedure for reuse. The TL emission spectra of LMB:Tb³⁺ showed broad green emission at 544 nm, which merged with host emission. The characteristic Tb³⁺ emissions are seen in the photoluminescence (PL) spectra.     

Dosimetric properties of rare earth doped LiCaBO3 thermoluminescence phosphors

Lithium Calcium borate (LiCaBO₃) polycrystalline thermoluminescence (TL) phosphor doped with rare earth (RE³⁺) elements has been synthesized by high temperature solid state diffusion reaction. The reaction has produced a very stable crystalline LiCaBO₃:RE³⁺ phosphors. Among these RE³⁺ doped phosphors thulium doped material showed maximum TL sensitivity with favorable glow curve shape. TL glow curve of gamma irradiated LiCaBO₃:Tm³⁺ samples had shown two major well-separated glow peaks at 230 and 430 °C. The glow peak at 430 °C is almost thrice the intensity of the glow peak at 230 °C. The TL sensitivity of the phosphor to gamma radiation was about eight times that of TLD-100 (LiF). Photoluminescence and TL emission spectra showed the characteristic Tm³⁺ peaks. TL response to gamma radiation dose was linear up to 10³ Gy. Post-irradiation TL fading on storage in room temperature and elevated temperatures was studied in LiCaBO₃:Tm³⁺ phosphor.     

Effect of 100 MeV swift Si8+ ions on structural and thermoluminescence properties of Y2O3:Dy3+nanophosphor

Nanoparticles of Y₂O₃:Dy³⁺ were prepared by the solution combustion method. The X-ray diffraction pattern of the 900°C annealed sample shows a cubic structure and the average crystallite size was found to be 31.49?nm. The field emission scanning electron microscopy image of the 900°C annealed sample shows well-separated spherical shape particles and the average particle size is found to be in a range 40?nm. Pellets of Y₂O₃:Dy³⁺ were irradiated with 100?MeV swift Si⁸⁺ ions for the fluence range of 3?×?10^11_3?×?10¹³ ions cm^?2. Pristine Y₂O₃:Dy³⁺ shows seven Raman modes with peaks at 129, 160, 330, 376, 434, 467 and 590?cm^?1. The intensity of these modes decreases with an increase in ion fluence. A well-resolved thermoluminescence glow with peaks at ～414?K (T_m1) and ～614?K (T_m2) were observed in Si⁸⁺ ion-irradiated samples. It is found that glow peak intensity at 414?K increases with an increase in the dopant concentration up to 0.6?mol% and then decreases with an increase in dopant concentration. The high-temperature glow peak (614?K) intensity linearly increases with an increase in ion fluence. The broad TL glow curves were deconvoluted using the glow curve deconvoluted method and kinetic parameters were calculated using the general order kinetic equation.     

Thermoluminescence characteristics of rare-earth-doped LiCaBO3 phosphor

LiCaBO₃ was synthesized by high-temperature solid-state reaction. The influence of different rare earth dopants, i.e. Dy³⁺, Tb³⁺, Tm³⁺ and Ce³⁺, on thermoluminescence (TL) of LiCaBO₃ phosphor was discussed. We studied the TL properties and some dosimetric characteristics of Ce³⁺-activated LiCaBO₃ phosphor in detail. The effect of the concentration of Ce³⁺ on TL was investigated, the result of which showed that the optimum Ce³⁺ concentration was 1 mol%. The TL kinetic parameters of LiCaBO₃:0.01Ce³⁺ were studied by computer glow curve deconvolution (CGCD) method. The three-dimensional (3D) TL emission spectra were also studied, peaking at 431 and 474 nm due to the characteristic transition of Ce³⁺. We also studied the linearity, annealing condition, reproducibility, fading and different heating rate of the LiCaBO₃:0.01Ce³⁺ phosphor.     

Effects of annealing and high radiation dose on the thermoluminescence characteristics of natural fluorite

In this study, the various dosimetric properties of the thermoluminescent (TL) phosphor of CaF₂:natural including response characteristics, sensitivity to thermal annealing and decay of stored energy were investigated in detail. The analysis of the peak temperature values and the half widths of the resolved components in the glow curves, by using the Computerized Glow Curve Deconvolution (CGCD) Method, resulted in the activation energy (E) of 0.85–1.83 eV and frequency factor (s) of 6.17E+9–2.90E+15 s^?1. The effects of pre-irradiation thermal annealing on the radiation-induced sensitization of the thermoluminescent response of CaF₂:natural were presented. An enhancement of sensitivity after being subjected to a high beta particle exposure was clarified. The effect was complicated by the influence of heat treatments before the exposure to radiation. Replicate runs on CaF₂:natural after irradiation with 1 Gy absorbed dose indicated good reproducibility of peak temperatures and intensities; they can be re-used for repeated measurements. It appeared that the main dosimetric peak at 280 °C exhibits negligible fading over 4 weeks and may be used for dosimetry. This study has demonstrated that the potential exists for the use of CaF₂:natural for TL radiation dosimetry.     

Thermo-luminescence kinetic parameters of γ-irradiated Sr4Al14O25:Eu2+, Dy3+ phosphors

In this paper, we present a detailed investigation of the thermo-luminescence (TL) kinetics of the long afterglow phosphor, Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺, synthesized by the combustion method. Kinetic parameters such as the activation energy (E_α), the frequency factor (s) and the order of kinetics (b) were calculated using Chen's formulism. The crystalline structure of the phosphor was examined using X-ray powder diffraction and transmission electron microscopy. The average particle size was found to be in the range of 45–52 nm. The optimum dopant concentrations were Eu (1 mol%) and that of Dy (2 mol%). The TL response of the phosphor was monitored after the samples were irradiated with a γ-dose using a ⁶⁰Co source in the 20-800 Gy range. A broad TL peak, (stretching from 328 to 410 K) with a maximum at 368 K was observed. With increasing irradiation dose, the main peak shifts toward higher temperatures. Symmetry factor calculations show that the main TL glow peak obeys second-order kinetics, which could be attributed to the creation of deep level traps. This means that γ-ray irradiation greatly affects the distribution of traps in the Sr₄Al₁₄O₂₅:Eu²⁺,Dy³⁺ phosphor. The phosphor showed a linear response with γ-dose.     

Luminescence investigations on sulfate apatite Na6(SO4)2FCl:RE (RE=Dy, Ce or Eu) phosphors

A new phosphor in the Cl-F system doped with Dy, Ce and Eu has been reported. Characterization of this phosphor using XRD, PL and TL techniques is described. Polycrystalline Na₆(SO₄)₂FCl:Dy; Na₆(SO₄)₂FCl:Ce and Na₆(SO₄)₂FCl:Eu phosphors prepared by a solid state diffusion method have been studied for their X-ray diffraction, photoluminescence (PL) and thermoluminescence (TL)characteristics. The PL excitation and emission spectra of phosphors were obtained. Dy³⁺ emission in the host at 475 and 570 nm is observed due to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transition, respectively, whereas the PL emission spectra of Na₆(SO₄)₂FCl:Ce phosphor shows the Ce³⁺ emission at 322 nm due to 5d→4f transition of Ce³⁺ ion. In Na₆(SO₄)₂FCl:Eu lattice, Eu²⁺ as well as Eu³⁺ emissions are observed. The emission of europium ion in this compound exhibits the blue as well as red emission. The TL glow curves of the same compounds have the simple structure with a prominent peak at 150, 175 and 200 °C. TL response, fading, reusability and trapping parameters of the phosphors are also studied. The TL glow curves of γ-irradiated Na₆(SO₄)₂FCl sample show one glow peak indicating that only one set of traps is being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The trapping parameters associated with the prominent glow peak are calculated using Chen’s half width method. The release of hole/electron from defect centers at the characteristic trap site initiates the luminescence process in these materials. The intensity of the TL glow peaks increases with increase of the added γ-ray dose to the samples.     

Investigation of thermoluminescence of natural zircon relevant to dating application

The thermoluminescence (TL) characteristics of natural zircons from Vietnam were studied for potential application to TL dating. All the glow curves of samples irradiated by gamma radiation or UV light showed a complex structure that consisted of a low temperature part (LTP) and a high temperature part (HTP). The TL emission spectra and monochromatic glow curves indicate that the two main impurities governing the TL emission are Dy³⁺ (LTP) and Tb³⁺ (HTP). The anomalous fading of the TL signal was assigned to the emission associated with Dy³⁺ whereas the 545 nm emission associated with Tb3⁺, exhibits significantly lower fading and consequently more suitable for TL dating.     

Phosphorescent and thermoluminescent properties of SrAl2O4:Eu,Dy phosphors prepared by solid state reaction method

Long persistent SrAl₂O₄:Eu²⁺ phosphors co-doped with Dy³⁺ were prepared by the solid state reaction method. The main diffraction peaks of the monoclinic structure of SrAl₂O₄ were observed in all the samples. The broad band emission spectra at 497 nm for SrAl₂O₄:Eu²⁺, Dy³⁺ were observed and the emission is attributed to the 4f⁶5d¹ to 4f⁷ transition of Eu²⁺ ions. The samples annealed at 1100–1200 °C showed similar broad TL glow curves centered at 120 °C. The similar TL glow curves suggest that the traps responsible for them are similar. The long afterglow displayed by the phosphors annealed at different temperatures, may be attributed to the Dy³⁺ ions acting as the hole trap levels, which play an important role in prolonging the duration of luminescence.     

Photoluminescence and thermoluminescence characterization of Eu- and Dy -activated Ca3(PO4)2 phosphor

Rare-earth-doped polycrystalline Ca₃(PO₄)₂:Eu, Ca₃(PO₄)₂:Dy and Ca₃(PO₄)₂:Eu,Dy phosphors prepared by a modified solid-state synthesis has been studied for its X-ray diffraction, thermoluminescence (TL) and photoluminescence (PL) characteristics. The PL emission spectra of the phosphor suggest the presence of Eu³⁺ ion in Ca₃(PO₄)₂:Eu and Dy³⁺ ion in Ca₃(PO₄)₂:Dy lattice sites. The TL glow curve of the Ca₃(PO₄)₂:Eu compounds has a simple structure with a prominent peak at 228 °C, while Ca₃(PO₄)₂:Dy peaking at 146 and 230 °C. TL sensitivity of phosphors are compared with CaSO₄: Dy and found 1.52 and 1.20 times less in Ca₃(PO₄)₂:Eu and Ca₃(PO₄)₂:Dy phosphors, respectively. The Ca₃(PO₄)₂:Eu,Dy phosphors shows switching behavior under two different excitation wavelengths and enhancement in PL intensity of Dy³⁺ ions were reported. The paper discusses the photoluminescence and thermoluminescence behavior of Eu³⁺ and Dy³⁺ ion in Ca₃(PO₄)₂ hosts, it may be applicable to solid-state lighting as well as thermoluminescence dosimetry applications.     

Luminescence studies of a combustion-synthesized blue–green BaAlxOy:Eu,Dy nanoparticles

Blue–green emitting BaAl_xO_y:Eu²⁺,Dy³⁺ phosphor was synthesized by the combustion method. The influence of various parameters on the structural, photoluminescence (PL) and thermoluminescence (TL) properties of the phosphor were investigated by various techniques. Phosphor nanocrystallites with high brightness were obtained without significantly changing the crystalline structure of the host. In the PL studies, broad-band excitation and emission spectra were observed with major peaks at 340 and 505 nm, respectively. The observed afterglow is ascribed to the generation of suitable traps due to the presence of the co-doped Dy³⁺ ions. Though generally broad, the peak structure of the TL glow curves obtained after irradiation with UV light was non-uniform with suggesting the contribution to afterglow from multiple events at the luminescent centers. Further insight on the afterglow behavior of the phosphor was deduced from TL decay results.     

Emission spectra of MgSO4:Dy,MgSO4:Tm and MgSO4:Dy,Mn phosphors

MgSO₄:Dy, MgSO₄:Tm and MgSO₄:Dy,Mn thermoluminescence (TL) phosphors have been prepared and their emission spectra were measured using a linear heater and optical multichannel analyzer. Emission bands at about 480, 580 and 660 nm of MgSO₄ doped with Dy were observed in three dimension (3D) glow curve. Emission bands about 360, 460, and 660 nm were observed in a 3D glow curve of MgSO₄ doped with Tm. The emission spectra of MgSO₄:Dy and MgSO₄:Tm are attributed to the characteristic emission wavelengths from transitions of Dy³⁺ and Tm³⁺ respectively. The results show that the structures of traps in matrix materials determine the activation energy distribution and dopant energy levels of rare earth ions are related with the emission spectrum wavelengths of sulfate phosphors. The intensities of the glow peaks in both bands at about 480 and 580 nm in MgSO₄ doped Dy and Mn were dramatically reduced in comparison with that of MgSO₄ doped Dy except above 300°C. It means that the trapping structures of MgSO₄ :Dy phosphor has greatly been altered by the co-dopant Mn but no change is observed in wavelengths of the emission spectra.     

Thermoluminescence studies of thermally treated CaB4O7:Dy

Borate based thermoluminescence dosimeters (TLD) show high sensitivity and good TL characteristics. One of the promising material amongst the dosimeters is Dy doped CaB₄O₇. Spectrally resolved thermoluminescence of Dy doped CaB₄O₇ shows three glow peaks at about 50 °C, 240 °C and 380 °C, the intensity of the 240 °C glow peak being the maximum. All TL experiments were conducted on a high sensitivity TL spectrometer at Sussex University with a heating rate of 50 °C min^?1. Two main emissions associated with the Dy dopant are observed at ～480 and 580 nm. The samples were subjected to a series of treatments including excitation by X-rays and UV laser radiation. As part of the present research CaB₄O₇:Dy materials were subjected to two different heat treatments; quenching and slow cooling in order to investigate the changes in TL characteristics.     

Investigation of the trap state of Sr2MgSi2O7: Eu2+, Dy3+ phosphor and decay process

The thermoluminescence glow curves of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ phosphor were measured after various delay times. A single trap center is confirmed that conforms to a kinetics model with order greater than 1, leading to a suppression of TL intensity and a high temperature shift of the TL peak with longer delay times. A constant trap depth supports this phenomenon. Further, the decay curve of the afterglow and the change in initial trapped carrier concentration can be fitted using general-order kinetics and the fitting results show that the afterglow is close to a second-order kinetics process, which implies that most of the released carriers are retrapped.     

Synthesis and TL glow curve analysis of BaSO4:Eu,Dy phosphor

The polycrystalline samples of Ba_1?x?ySO₄:Eu_x,Dy_y (0≤x≤1, 0≤y≤1) have been prepared using the chemical co-precipitation technique. The thermoluminescence (TL) sensitivity of the samples have been found changing with the value of x and y and the highest TL intensity is for Ba₉₆SO₄:Eu₀₂,Dy₀₂. The sample has been characterised by x-ray diffraction (XRD). The samples are found to have orthorhombic structure. For TL analysis Ba₉₆SO₄:Eu₀₂,Dy₀₂ is annealed at different temperatures ranging from 873 to 1173 K. Kinetic parameters of all the TL glow curves of Ba_1?x?ySO₄:Eu_x,Dy_y for different values of x and y and also for the TL glow curves Ba₉₆SO₄:Eu₀₂,Dy₀₂ annealed at different temperatures have been found out using computerised glow curve deconvolution (CGCD) method. The activation energy for the most intense TL peak at (444–453 K) is found out to be 1.26 eV and order of kinetics is 1.35.     

Thermoluminescence studies of LiBa2B5O10:RE (RE=Dy, Tb and Tm)

LiBa₂B₅O₁₀:RE³⁺ (RE=Dy, Tb and Tm) was synthesized by the method of high-temperature solid-state reaction and the thermoluminescence (TL) properties of the samples under the irradiation of the γ-ray were studied. The result showed that Dy³⁺ ion was the most efficient activator. When the concentration of Dy³⁺ was 2 mol%, LiBa₂B₅O₁₀:Dy³⁺ exhibited a maximum TL output. The kinetic parameter of LiBa₂B₅O₁₀:0.02Dy was estimated by the peak shape method, for which the average activation energy was 0.757 eV and the frequency factor was 1.50×10⁷ s⁻¹. By the three-dimensional (3D) TL spectrum, the TL of the sample was contributed to the characteristic f-f transition of Dy³⁺. The dose-response of LiBa₂B₅O₁₀:0.02Dy to γ-ray was linear in the range from 1 to 1000 mGy. In addition, the decay of the TL intensity of LiBa₂B₅O₁₀:0.02Dy was also investigated.     

Thermoluminescence of B2O3-Li2O glass system doped with MgO

Lithium borate (LiB) glasses in the system (100−x)B₂O₃-xLi₂O with x=20, 30, 40, 50, 60 and 70 mol% were prepared. The glasses were doped with different concentrations of the order of 10⁻¹, 10⁻², 10⁻³, 10⁻⁴ and 10⁻⁵ of MgO and their thermoluminescent (TL) response was investigated. The irradiations were performed using γ rays from a ⁶⁰Co source in the dose range from 0.1 to 25 kGy. The material displayed good sensitivity for γ-rays and intensity of TL signals is dependent on γ-ray dose and Li₂O content. For each dose level and investigated temperature range (50-350 °C), exactly single isolated glow peak appears in the temperature range of 165-205 °C depending on both Li₂O concentrations and time of exposure. The shape of the glow peak has altered significantly with increase in the gamma ray dose or Li₂O concentrations. The glass composition with x=50 mol% doped with 10⁻³ mol% of MgO presented the best TL response. The results of the present study indicated that the recorded single and isolated high temperature peak is a good candidate for TL dosimetric investigations. This indicates that 50 B₂O₃-50Li₂O-doped with 10⁻³ mol% of MgO is possibly used as materials for radiation dosimetry in the dose range of 0.1-20 kGy.     

Studies on luminescence properties and energy transfer in Ce/Dy co-doped CaS nano-phosphors

Luminescence properties of CaS:Ce co-doped with dysprosium has been studied. Ce/Dy co-doped CaS nanophosphors (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50, CaS:Ce_0.75Dy_0.25) were synthesized using the solid state diffusion method. The phase purity of the samples was confirmed using XRD data. The particle size was calculated using Debye–Scherrer formula and was found to be varying between 50 and 60 nm for all the three samples (CaS:Ce_0.25Dy_0.75, CaS:Ce_0.50Dy_0.50 and CaS:Ce_0.75Dy_0.25). TEM image analysis of CaS:Ce_0.50Dy_0.50 shows nearly spherical particles with diameter varying between 50 and60 nm. One way energy transfer from Dy³⁺ to Ce³⁺ in CaS host has been investigated using photoluminescence studies. Thermoluminescence of these nanophosphors has been studied for 0.5 Gy–21 kGy dose of gamma rays and the dose linearity of CaS:Ce_0.50Dy_0.50 has been compared with CaSO₄:Dy (standard TL dosimeter). Linear behavior over a large dose range between 0.5 Gy and 21 kGy was found for CaS:Ce_0.50Dy_0.50 as compared to CaSO₄:Dy (nanocrystalline and microcrystalline) but it is found to be less sensitive than microcrystalline CaSO₄:Dy. To identify the peaks of Ce³⁺ and Dy³⁺ in CaS, the TL spectra of CaS, CaS:Ce, CaS:Dy and CaS:Ce_0.50Dy_0.50 were recorded. The addition of dopants does not add new peaks in CaS but aid to enhance the TL emission. The peaks in CaS may be associated to intrinsic traps in the host lattice.     

Correlated ESR, PL and TL studies on Sr5(PO4)3Cl:Eu thermoluminescence dosimetry phosphor

Electron spin resonance (ESR), thermoluminescence and photoluminescence studies in Eu²⁺ activated Sr₅(PO₄)₃Cl phosphor are reported in this paper. The Sr₅(PO₄)₃Cl:Eu²⁺ phosphor is twice as sensitive as the conventional CaSO₄:Dy phosphor used in thermoluminescence dosimetry of ionizing radiations. It has a linear response, simple glow curve, emission peaking at 456 nm. The defect centers formed in the Sr₅(PO₄)₃Cl:Eu²⁺phosphor are studied by using the technique of ESR. A dominant TL glow peak at 430 K with a smaller shoulder at 410 K is observed in the phosphor. ESR studies indicate the presence at three centers at room temperature. Step annealing measurements show a connection between one of the centers and the dominant glow peak at 430 K. The 430 K TL peak is well correlated with center I, which is tentatively identified as (PO₄)²⁻ radical.     

Thermoluminescence study of aluminum oxide doped with therbium and thulium

In this work, α-Al₂O₃ doped either with Tb³⁺ or Tm³⁺ was prepared by combustion synthesis techniques for thermoluminescent (TL) ionizing radiation dosimetry applications. In this method, the reactants (aluminum nitrate, urea and therbium or thulium nitrate) are ignited in a muffle furnace at temperatures as low as 500 °C. This synthesis route is an alternative technique to the conventional fabrication methods of materials based on α-Al₂O₃ (Czochralsky, Vernuil), where high melting temperatures and reducing atmospheres are required. After combustion, the samples were annealed at temperatures ranging from 1000 to 1400 °C for 4 h in order to obtain the pure α-phase structure and were then irradiated with a Co-60 gamma radiation source. The annealed samples present a well defined TL glow peak with a maximum at approximately 200 °C and linear TL response in the dose range 0.5–5 Gy. It was observed that a 0.1 mol% concentration of Tb³⁺ or Tm³⁺ and annealing at 1400 °C optimize the TL sensitivity. The highest sensitivity was found for Tm³⁺ doped samples which were approximately 25 times more sensitive than Tb³⁺ doped samples. These results strongly suggest that combustion synthesis is a suitable technique to prepare doped aluminum oxide material and that Tm³⁺ doped aluminum oxide is a potential material for TL radiation dosimetry.