Synthesis, photoluminescence, thermoluminescence and dosimetry properties of novel phosphor Zn(BO2)2:Tb

Polycrystalline powder samples of terbium doped Zn(BO₂)₂ phosphors were prepared by solid state reaction in the thermal carbon reducing atmosphere at high temperature. The photoluminescence (PL), three-dimensional (3D) TL emission spectrum and dosimetric characteristics following ⁶⁰Co gamma-rays irradiation were studied. Characteristic emission bands of Tb³⁺ at about 490, 543, 584 and 620 nm, attributed to the ⁵D₄→⁷F_J (J=3, 4, 5, 6) transitions of Tb³⁺ ions, were observed in the TL and PL emission spectrum. No emission from Tb⁴⁺ ions was observed in the TL emission spectrum. The TL-dose response of the powder samples Zn(BO₂)₂:Tb to ⁶⁰Co gamma-rays radiation in the dose range from 1 to 100 Gy for clinical dose levels was almost linear. The experiment results showed that Zn(BO₂)₂:Tb has potential use as the materials of gamma-rays thermoluminescence dosimeter (TLD) for clinical dosimetry.     

Investigation of defect centres responsible for TL/OSL in MgAl2O4:Tb

Magnesium aluminate doped with Tb³⁺ (MgAl₂O₄:Tb³⁺) was prepared by combustion synthesis. Three thermoluminsence (TL) peaks at 120, 220 and 340 °C were observed. PL and TL emission spectrum shows that Tb³⁺ acts as the luminescent centre. Optically stimulated luminescence (OSL) was observed when stimulated by 470 nm blue light.Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the TL and OSL processes in MgAl₂O₄:Tb³⁺. Two defect centres were identified in irradiated MgAl₂O₄:Tb³⁺ phosphor by ESR measurements which was carried out at room temperature and these were assigned to V and F⁺ centres. V centre (hole centre) is correlated to 120 and 220 °C TL peaks and F⁺ centre (electron centre), which acts as a recombination centre is correlated to 120, 220 and 340 °C.     

Photoluminescence and EPR studies on gamma irradiated Ce doped potassium halide single crystals

Electron Paramagnetic Resonance(EPR), Photoluminescence(PL), Thermoluminescence (TL) and other optical studies of γ-irradiated KBr, KCl:Ce³⁺ single crystals. Cerium when doped into the KBr, KCl is found to enter the host lattice in its trivalent state and act as electron trap during γ-irradiation, thereby partially converting itself to Ce²⁺. The Photoluminescence(PL) spectra of both KCl and KBr crystals doped with Ce exhibit the strong blue emissions of Ce corresponding to ⁵d(²D)→²F_5/2 and ⁵d(²D)→²F_7/2 transitions. The defect centers formed in the Ce³⁺ doped KBr and KCl. Crystals are studied using the technique of EPR. A dominant TL glow peak at 374, 422 K and KCl:Ce³⁺ at 466, 475 K is observed in the crystal. EPR studies indicate the presence at two centers at room temperature. Spectral distribution under the thermoluminescence emission(TLE) and optically stimulated emission(OSL) support the idea that defect annihilation process to be due to thermal release of F electron in KBr, KCl:Ce³⁺ crystals. Both Ce³⁺ and Ce²⁺ emissions were observed in the thermoluminescence emission of the crystals.     

Thermoluminescent analysis of CaSO4:Tb,Eu crystal powder for dosimetric purposes

The motivation of this work was to produce crystals of CaSO₄ doped with an unusual combination of RE elements such as terbium (Tb) and europium (Eu) in different concentrations, and analyze its thermoluminescent (TL) properties. The crystals were produced by the slow evaporation route using calcium carbonate (CaCO₃) as precursor, and incorporating the dopants (Tb₂O₃ and Eu₂O₃) in a solution of sulfuric acid, that is evaporated and collected again, leaving just CaSO₄:Tb,Eu crystal powder. The terbium and europium ions were incorporated in concentration ratios of 1:1, 2:1 and 5:1 (weight proportions). X-ray diffraction analyses showed that samples of doped CaSO₄ exhibit only a single phase corresponding to the crystal structure of anhydrite. The radioluminescence confirmed the presence of Tb³⁺ and Eu²⁺ in the crystal matrix. The CaSO₄:Tb,Eu crystal powders showed TL emission glow curves with three peaks centered around 170 °C, 270 °C and 340 °C, after irradiation with a ⁹⁰Sr/⁹⁰Y source. Thermoluminescent (TL) characteristics such as linearity, reproducibility and fading were evaluated. Samples produced with concentration ratio of 2:1 of Tb and Eu showed the highest TL intensity. The produced CaSO₄:Tb,Eu samples present TL properties useful for dosimetric purposes.     

Energy transfer induced Eu3+ photoluminescence enhancement in tellurite glass

In this work, structural, thermal and optical properties of Eu³⁺ doped TeO₂–La₂O₃–TiO₂ glass were investigated. The differential scanning calorimetry (DSC) measurements reveal an important stability factor ΔT=143.52 K, which indicates the good thermal and mechanical stabilities of tellurite glass. From the absorption spectrum, the optical band gap was found to be direct with E_g=3.23 eV. The temperature dependences of photoluminescence (PL) properties of Eu-doped and Eu–Tb codoped tellurite glass are investigated. As the temperature increases from 7 to 300 K, both the PL intensity and the PL lifetime relative to the ⁵D₂→⁷F₀ are nearly constant below 230 K and then an enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from charged intrinsic defects states to Eu³⁺ energy levels.By co-doping tellurite glasses with Eu and Tb, a strong Eu³⁺ PL enhancement is shown due to excitation transfer from Tb³⁺ and intrinsic defects to Eu ions.     

Thermoluminescence and optically stimulated luminescence characteristics of Al2O3 doped with Tb

In the present work policrystals of α − Al₂O₃ doped with terbium were synthesized using the solvent evaporation method. The samples were prepared using Al(NO₃)₃·9H₂O and Tb(NO₃)₃·5H₂O reagents, with Tb concentrations between 1 and 5 mol% and thermally treated at high temperature above ∼1400 °C. X-ray diffraction measurements showed the α-phase formation of samples. TL glow curve presented an intense peak at ∼190 °C and two other with low intensity at 290 and 350 °C after gamma irradiation. The best doping concentration which presented high luminescence was the sample doped with 3 mol% of Tb. TL spectra and fluorescence measurements showed similar luminescence spectra with lines attribute to Tb³⁺ ions. A linear behavior to gamma dose between 1 and 20 Gy was observed in TL, using 190 °C peak as well as in OSL signal, this last carried out using 532 nm wavelength stimulation.     

Effect of Tb3+ co-doping and particle size on K2Ca2(SO4)3:EU phosphor

K₂Ca₂(SO₄)₃ doped with Eu, and co-doped with Tb were prepared by the solid state diffusion method. The nanoparticles of these phosphors were also prepared by the chemical co-precipitation method. The formation of the compounds was confirmed by XRD. The particle size was calculated by the broadening of the XRD peaks using Scherrer's formula. The particle size was found to be around 20?nm. Thermoluminescence (TL) was studied to see the effect of co-doping and particle size. Tb³⁺ co-doping decreases the intensity in the Eu²⁺ doped phosphor due to the energy transfer and multiple de-excitations through various radiative and non-radiative processes. The K₂Ca₂(SO₄)₃:Eu,Tb phosphor is found to be 0.33 times more sensitive than TLD-700H, but around 15 times more than LiF-TLD 100, and 7 times more than CaSO₄:Dy. The effective atomic number Z_eff is around 15, which is again comparable to CaSO₄:Dy.

However, very low sensitivity was observed in the case of nanoparticles. The decrease in the sensitivity is attributed to the particle size effect i.e., the volume-to-surface ratio. Study of photoluminescence (PL) of the material is also carried out.     

Synthesis and luminescence in some fluoro-silicates for the possible applications in OSL dosimetry

Various fluoro-silicates, viz. M₂SiF₆ (M=Li, Na, K) were synthesized by reacting the mixture of corresponding salt and silicic acid with Hydrofluoric acid. The thermal analysis of these materials was performed. These materials were doped with ions Ce³⁺, Cu⁺, Ag⁺ and photoluminescence, TL, OSL properties were studied. Intense TL and OSL was observed from these materials. Due to decomposition during heating, these materials may not be suitable as TL Phosphors, but will be good phosphors for radiation dosimetry using OSL.     

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.     

Radiation induced defects in KBr:Tl+ crystals

The defects produced in KBr:Tl⁺ crystals during x-irradiation at 77 K were studied using thermoluminescence (TL), thermally stimulated currents (TSC), and absorption and emission spectra. Three main glow peaks at 165, 193 and 258 K were observed both in the TL and in the TSC curves. A variety of irradiation induced absorption bands were observed in the UV, visible and infrared up to about 2 microns. The 165 K TL peak was found to emit only the 440 nm band assigned to thallium dimers, while the peaks at 193 and 258 K exhibited the UV bands at 310 and 365 nm as well as the 440 nm band.The defects produced during the irradiation were the V_k hole center, the Tl° and the Tl⁺₂ electron centers. Smaller concentrations of Tl²⁺ and (Tl⁺)⁺₂ centers were also produced.An analysis of the results including measurements on lightly and heavily doped crystals enabled to draw conclusions on the nature of the defects and on the recombination processes involved. A close correlation has been found between the temperatures at which changes in the various absorption bands take place and the temperatures of the TL peaks. The analysis enabled also a full classification of the absorption bands.     

Thermoluminescence and photoluminescence studies on gamma irradiated CsI: Pb2+ crystals

Pure and Pb²⁺-doped CsI crystals have been grown by the Bridgemann technique. Optical absorption, thermoluminescence (TL) and photoluminescence (PL) measurements have been performed. In undoped and Pb²⁺-doped cesium iodide crystals, F-centers and V-centers have been produced at 770 nm and 350 nm, respectively. In Pb²⁺-doped crystals, additional centers at 373 nm, 290 nm and 258 nm bands have been produced. In undoped samples, only two glow peaks at 343 K and 373 K have been produced, and in Pb²⁺-doped samples additional glow peaks at 383 K and 423 K have been produced. For all the samples, TL emission, PL and excitation measurements have been performed.     

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.     

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.     

Enhanced luminescent properties and optical absorption of γ-irradiated KI: Ce, Tb crystals

This paper reports that KI doped with Ce³⁺ or double doped with Tb³⁺ and Ce³⁺ were prepared by the Bridgman-Stockbarger method and characterized by optical absorption photoluminescence (PL), thermoluminescence (TL), photostimulated emission (PSL) and TL emission. The optical absorption measurement indicates that F and V₁, V₂ centers are formed in the crystals during the γ irradiation process. It was attempted to incorporate a broad band of Ce³⁺ activator into the narrow band emission of Tb³⁺ in the KI host without the reduction of emission intensity. Ce³⁺-co-doped KI and Tb crystals showed a broad band emission due to the d-f transition of Ce³⁺ and a reduction in the intensity of emission peaks due to the ⁵D₃-⁷F_j (j=3,4,5,6) transition of Tb³⁺, when they were excited at 240 nm.These results supported that an effective energy transfer occurs from Tb³⁺ to Ce³⁺ in the KI host. Co-doping Ce³⁺ ions greatly intensified the excitation peak at 260 nm for the emission at 393 nm of Tb³⁺, which means that more lattice defects, involved in the energy absorption and transfer to Tb³⁺, are formed by the Ce³⁺ co-doping. The integrated light intensity is an order of magnitude higher as compared to the undoped samples for similar doses of irradiation and heating rates. The defects generated by irradiation were monitored by optical absorption and TSL Trap parameters for the TL process are calculated and presented.     

D3→FJ emission of Tb doped sol–gel silica

Amorphous silica samples doped with 0.1 and 1 mol% of terbium (Tb) were synthesized by the sol–gel method. In addition to the green light associated with ⁵D₄→⁷F_J transitions of Tb³⁺, the sample containing 0.1 mol% also emitted blue light as a result of ⁵D₃→⁷F_J transitions during photoluminescence (PL) measurements. As a result of concentration quenching this blue emission was not observed for the samples doped with the higher concentration (1 mol%). However the blue ⁵D₃ →⁷F_J emission was observed in the 1 mol% doped samples during cathodoluminescence (CL) measurements. Since a rough calculation indicated that the excitation rate in the CL system where the blue emission is observed may be similar to a laser PL system under conditions where the blue emission is not observed, the difference is attributed to the nature of the excitation sources. It is suggested that during the CL excitation incident electrons can reduce non-luminescent Tb⁴⁺ ions in the silica, substituting for Si⁴⁺ ions, to the excited (Tb³⁺)? state and that these are responsible for the blue emission, which does not occur during PL excitation.     

Rare earth doped lithium titanate (Li2TiO3) for potential phosphor applications

Lithium titanate ceramics doped with three rare earth (RE) ions namely Eu³⁺, Dy³⁺ and Tb³⁺ were synthesized and their photoluminescence (PL) properties were investigated. PL spectra of Eu doped sample showed peaks corresponding to the ⁵D₀→⁷F_j (j=0, 1, 2, 3 and 4) transitions under 230 nm excitation. Strong red emission coming from the hypersensitive ⁵D₀→⁷F₂ transition of Eu³⁺ ion suggested the presence of the dopant ion in a highly asymmetric environment. Dy doped samples showed the Dy³⁺ emission characteristic due to ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions. Their relative intensity ratios also suggested the presence of asymmetric environment around the metal ion. In case of the Tb³⁺ doped sample blue-green emission corresponding to the ⁵D₄→⁷F_j (j=6, 5 and 4) transitions was seen. The fluorescence lifetimes of Eu³⁺, Dy³⁺ and Tb³⁺ ions were found to be 645, 900 and 740 μs, respectively. PL intensity of the individual rare earth doped samples was compared with commercial red and green phosphors. It was found that the emission from Eu doped titanate sample was 46% of the commercial red phosphor and in case of the Tb samples it was 30% when excited at 230 nm. However, the synthesized Eu doped titanate sample showed better color purity as compared to the commercial phosphor. The titanate host was doped with all the three rare earths to get white light emission from the system. The individual rare earth ion content was optimized so as to get a near white light emission. The color coordinates of the triple doped systems were evaluated and plotted on the CIE x–y diagram. Our results suggest that lithium titanate has enough potential to be a phosphor material.     

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.     

Luminescent properties of Dy doped SrMoO4 phosphor

Trivalent dysprosium ions (Dy³⁺) doped strontium molybdate (SrMoO₄) phosphors were synthesized by solid-state reaction and their photoluminescence (PL) properties were investigated. X-ray powder diffraction (XRD) analysis confirmed the formation of SrMoO₄:Dy³⁺. PL measurements indicated that the phosphor exhibited intense emission at 482, 490 (⁴F_9/2→⁶H_15/2) and 575 nm (⁴F_9/2→⁶H_13/2) under UV excitation. The effect of the doping concentration of Dy³⁺in SrMoO₄:Dy³⁺ on the PL was investigated in detail. Na⁺ ion was a good charge compensator for SrMoO₄:Dy³⁺.     

Luminescence characteristics of K2Ca2(SO4)3:Eu,Tb micro- and nanocrystalline phosphor

K₂Ca₂(SO₄)₃ microcrystalline pure, doped with Eu, Tb and co-doped with Eu, Tb was prepared by solid-state diffusion method. Nanoparticles of these phosphors were also prepared by the chemical co-precipitation method. The formation of the compounds was confirmed by XRD. The particle size was calculated by broadening of the XRD peaks using Scherrer's formula. The particle size of nanocrystalline powder material was approximately found to be around 20 nm. Thermoluminescence and photoluminescence were studied to see the effect of co-doping and particle size. Tb³⁺ co-doping decreases the intensity in the Eu²⁺ doped phosphor due to the energy transfer and multiple de-excitations through various radiative and non-radiative processes. The sensitivity of K₂Ca₂(SO₄)₃:Eu,Tb microcrystalline phosphor was around 15 times more than LiF-TLD 100 and 7 times more than CaSO₄:Dy. A high temperature peak (615 K) was observed in case of the nanoparticles, which was attributed to a particle size induced phase transition. This was confirmed by differential scanning calormetry measurements. The decrease in the sensitivity in case of nanoparticles is attributed to the particle size effect i.e. volume to surface ratio. Theoretical analysis of the glow curves was done by glow curve convolution deconvolution method to calculate trapping parameters of various peaks.     

Luminescence study of γ-ray and C5+ ion beam-irradiated LiCaBO3:Cu phosphor

Cu-doped LiCaBO₃ phosphors were prepared by modified solid-state synthesis and the formation of compound was confirmed by X-ray diffraction study. LiCaBO₃:Cu⁺ (Cu?=?0.02, 0.05, 0.1 and 0.2?mol%) were studied for photoluminescence (PL) study and prominent PL emission spectra were obtained for Cu⁺ with transition ³d₉⁴s₁?→?³d₁₀. The phosphors were further studied by thermoluminescence (TL) property for exposure to γ-ray irradiation of 1.2?rad with ¹³⁷Cs source. TL of LiCaBO₃:Cu was also studied for C⁵⁺ (3.75?×?10¹²?ion?cm^?2) beam irradiation for 1?min exposure time. Trapping parameters (activation energy and frequency factor) for single deconvoluted peaks were obtained by Chen's peak shape method.