Synthesis, photoluminescence, thermoluminescence and electron spin resonance investigations of CaAl12O19:Eu phosphor

The present paper describes the synthesis of europium-doped calcium aluminate phosphor using the combustion method. An efficient blue emission phosphor can be prepared at reaction temperatures as low as 500 °C in a few minutes by this method. Characterization of the powder was done by X-ray diffraction, transmission electron microscopy, scanning electron microscope analysis and the optical properties were studied by photoluminescence spectra. Thermoluminescence (TL) studies also have been carried out on CaAl₁₂O₁₉:Eu²⁺ phosphor. The TL glow curve shows peaks at 174 and 240 °C. Defect centres formed in irradiated phosphor have been studied using the technique of electron spin resonance. Step annealing measurements indicate that one of the annealing stages of a defect centre appear to correlate with the release of carriers resulting in TL peak at 174 °C. The centre is characterized by an isotropic g-value of 2.0046 and is assigned to a F⁺ centre.     

Thermoluminescence and opitical absorption of BaF2 crystals

Abstract

Nominally pure and Dy-doped BaF₂ crystals were investigated concerning their optical absorption (OA) and thermoluminescence (TL) properties. Peaks at 120—150 and 200°C were observed for a heating rate of 1.7°C/s. The TL response for γ-rays and the TL emission spectra were obtained for these peaks. Except for the purest crystal, all BaF₂ crystals produced OA bands before irradiation typical of Ce³⁺ ions. After irradiation, Dy doped crystals showed bands due to Dy²⁺ ions. A nominally pure sample gave bands related to Ce²⁺ ions and photochromic centers of Ce³⁺ ions. and photochromic centres of Ce³⁺ ions. The correlation between some OA bands and TL peaks is discussed.     

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.     

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.     

Up and down conversion fluorescence studies on combustion synthesized Yb/Yb: MO-Al2O3 (M=Ca, Sr and Ba) phosphors

The ytterbium ions doped MO-Al₂O₃ (M=Ca, Sr and Ba) phosphors have been synthesized through combustion technique and their up and down conversion fluorescence properties have been studied and compared. The samples were calcinated at different temperatures and their FTIR and XRD spectra have shown a close relationship. With 976 nm excitation all these phosphors show cooperative upconversion emission at 488 nm from the pairs of two Yb³⁺ ions along with an unexpected broad upconversion band in the blue green region and has been assigned to arise from the defect centers. Contrary to this upconversion emission, calcium aluminate phosphor exhibits bright and very broad down-conversion fluorescence (FWHM≈160 nm) upon UV (266 nm) excitation due to Yb²⁺ ions. The inter-conversion between the 3+ and 2+ valence states of Yb ion has been observed on calcinations of samples in open atmosphere and has been correlated to the emission properties. The Yb²⁺ ions containing calcium aluminate phosphor has been found suitable for producing broad band light in the visible region (white light). Lifetime of the emitting states of Yb³⁺ and Yb²⁺ ions have also been measured and discussed.     

Behaviour of F and Fz Centres Under Thermal Stimulation in KCl:Eu2☎ Irradiated with Ionizing and UV Radiation

The optical absorption (OA) of F and F_z, centres in beta-and UV-irradiated KCl: Eu^2? have been studied. The spectra measured at room temperature and during the subsequent heatings up to 600 K, were analyzed by a deconvolution procedure. The OA bands of the F and F_z centres are well described respectively by asymmetric and symmetric gaussiane with parameters that are linearly dependent on the temperature. The thermal stability of the F_z centres correlates with the low-temperature thermostimulated luminescence (TL) peaks. The stability of the F centres is determined at least by two processes. Part of the F centres is destroyed together with the F_z centres. The remaining ones are destroyed during further heating up to 470 K, correlating with the TL peak at 425 K (at heating rate of 0.1 K/s).     

Modelling the optical bleaching of the thermoluminescence of K2YF5:Pr3+

Optical bleaching of the thermoluminescence (TL) curve of K₂YF₅:Pr³⁺ has been observed after optically stimulated luminescence (OSL) readout of pre-irradiated crystals. The traps being responsible for the TL signal are not emptied completely by the optical stimulation. Furthermore, if the illumination time is increased a constant intensity level of the residual TL glow curve is eventually achieved. On the other hand, if the low temperature peak of the glow curve is thermally cleaned, no subsequent OSL is measured. This behavior has been successfully explained by assuming that part of the electrons in the trap being responsible for the low temperature glow peak of K₂YF₅:Pr³⁺ recombine with holes via localized transitions during optical stimulation. During TL all trapped electrons recombine via delocalized transitions. Simulations have been carried out in order to demonstrate the feasibility of the model.     

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.     

TL,OA and ESR of spessartine garnet

Thermoluminescence (TL), optical absorption (OA), electron spin resonance (ESR) and their relation to point defects in spessartine have been investigated. The TL glow curve presented four peaks at 150, 220, 260 and 335 °C. The 150 and 335 °C TL peaks growth curves presented a linear growth with radiation dose up to about 400 Gy, supralinearity above this dose, and saturation around 800–1000 Gy. The OA spectrum presented allowed spin transition bands due to Fe³⁺ and Mn²⁺ in dodecahedral environment. Absorption bands due to ultraviolet charge transfer of Fe³⁺ in octahedral and tetrahedral positions were also observed. Two ESR, a strong one around g?～?2 due to Fe³⁺ in octahedral position, and another weaker one at g?～?4 due to Fe³⁺ in tetrahedral position, have been detected. The effect of high temperature annealing (600–900 °C) before irradiation was also investigated.     

Analysis of TL and OSL kinetics of lithium aluminate

Lithium aluminate (LiAlO₂) polycrystalline material showing high OSL sensitivity and linear dose response was prepared at IFJ Krakow. The kinetic parameters of OSL and TL processes were evaluated using various experimental techniques: LM-OSL deconvolution, TL glow-curve deconvolution, variable heating rate and isothermal decay. The OSL signal was found to consist of four components, one of them exhibiting a very slow decay. The TL glow-curve possesses two apparent peaks at approximately 85 °C and at 165 °C, which both seem to follow first order kinetics. These peaks seem to have a composite structure and as many as six peaks were found in the glow-curve.     

α-Al2O3:C晶体的热释光和光释光特性

以高纯α-Al₂O₃和石墨为原料,采用温梯法生长了α-Al₂O₃：C晶体,使用Ris TL/OSL-DA-15型热释光和光释光仪研究了其热释光和光释光特性.α-Al₂O₃：C晶体在462K附近有单一热释光峰,发射波长位于410nm.随着辐照剂量的增加,热释光强度逐渐增强,462K的热释光特征峰位置保持不变.α-Al₂O₃：C晶体的 关键词： 2O₃：C')" href="#">α-Al₂O₃：C 热释光 光释光     

Synthesis and investigation of the luminescent properties of carbon doped lanthanum aluminate (LaAlO3) for application in radiation dosimetry

LaAlO₃ single crystals grown under hydrothermal conditions and co-doped with Ce and Dy atoms have been recently reported to show high thermoluminescent (TL) outputs for ultraviolet (UV) radiation fields (Oliveira et al., 2011). Due to this property, they have been considered for further investigation for applications in UV dosimetry. Encouraged by these results, we start an investigation about the TL properties of polycrystalline LaAlO₃ grown by an alternative method. In this method, equimolar amounts of Al₂O₃ and La₂O₃ are sintered, producing polycrystalline LaAlO₃ powder. Polycrystals doped with amounts of carbon ranging from 0.0 to 5.0 at.% were synthesized by sintering under hydrogen reducing atmosphere. After irradiation with a UV commercial lamp, the best TL outputs were observed for the undoped sample. The recorded TL glow curves show a main TL peak centered at 175 °C. The TL emission spectrum show a broad emission peak centered at 634 nm and another three narrow peaks centered at 724 nm, 738 nm and 754 nm, respectively. The undoped material show a huge TL output response for UV spectral irradiances ranging from 0.04 to 1.68 mJ cm⁻² that can be fitted by a 2nd order polynomial regression. The investigation demonstrates that undoped polycrystalline LaAlO₃ crystals sintered under reducing atmosphere are very attractive to be investigated as high sensitivity ultraviolet TL dosimeters.     

Comparative investigations of TL and OSL in KCI:Eu2+ crystals irradiated with UV and X-rays

Abstract

We present thermoluminescence (TL) glow curves and optical stimulated luminescence (OSL) response from both KCl:Eu²⁺ crystals irradiated with soft X-rays (20 KV, 80 μA) and ultraviolet light (230 nm). Two situations take place. First, we observed that for long time F-light bleaching (560 nm) the typical TL glow curve of X-rays irradiated KCl:Eu²⁺ resembles the TL glow curve of UV-irradiated samples. Second, along with OSL measurements, we have performed a thermal bleaching and we have addressed F and F_z participation in OSL. These results provide us a supportable correlation between F and F_z as responsible centers for OSL and TL processes.     

Preliminary TL Studies of K2GdF5:Dy3+ exposed to photon and neutron radiation fields

Results of the investigation concerning thermoluminescence (TL) responses to X, gamma and neutron radiation fields for crystals of complex fluoride K₂GdF₅ undoped and doped with varying concentrations of Dy³⁺ ions are presented. Crystals doped with 5.0 at% Dy³⁺ have shown the most efficient TL response, with a linear response to doses for all the radiation fields. In the X rays range, the maximum TL response has been found to be 15 times more than the response for gamma. The fast and thermal neutron TL outputs were evaluated for K₂Gd_0.95Y_0.05F₅ and the contribution of the gamma component in the TL curve was estimated.     

Comparative study of pulsed laser deposited HfO2 and Hf–aluminate films for high-k gate dielectric applications

The thermal stability and the electrical properties of HfO₂ and Hf–aluminate films prepared by the pulsed laser deposition technique have been investigated by X-ray diffraction, differential thermal analysis, capacitance–voltage correlation, leakage-current measurements and high-resolution transmission electron microscopy observation, respectively. A crystallization transformation from HfO₂ amorphous phase to polycrystalline monoclinic structure occurs at about 500 °C. In contrast, the amorphous structure of Hf–aluminate films remains stable at higher temperatures up to 900 °C. Rapid thermal annealing at 1000 °C for 3 min leads to a phase separation in Hf–aluminate films. Tetragonal HfO₂(111) is predominant, and Al₂O₃ separates from Hf–aluminate and is still in the amorphous state. The dielectric constant of amorphous HfO₂ and Hf–aluminate films was determined to be about 26 and 16.6, respectively, by measuring a Pt/dielectric film/Pt capacitor structure. A very small equivalent oxide thickness (EOT) value of 0.74 nm for a 3-nm physical thickness Hf–aluminate film on a n-Si substrate with a leakage current of 0.17 A/cm² at 1-V gate voltage was obtained. The interface at Hf–aluminate/Si is atomically sharp, while a thick interface layer exists between the HfO₂ film and the Si substrate, which makes it difficult to obtain an EOT of less than 1 nm. PACS 77.55.+f; 81.15.Fg; 73.40.Qv     

Thermoluminescence and photoluminescence characteristics of K2YF5: Tb3++PTFE irradiated with 90Sr/90Y beta particles

This article presents results of thermoluminescence (TL) and photoluminescence (PL) measurements performed on beta-irradiated K ₂YF ₅:Tb ³⁺+PTFE pellets. K ₂YF ₅ crystals doped with 0.1% of trivalent optically active Tb ³⁺ ions in pellets form were investigated. The TL glow curve of K ₂YF ₅:Tb ³⁺+PTFE has a simple structure with two well-defined peaks centered at 170 and 307 °C. The TL sensitivity of the K ₂YF ₅:Tb ³⁺+PTFE irradiated with beta radiation was found to be higher than that of commercial phosphor TLD-100 (LiF:Mg,Ti), at the same conditions of irradiation and readout. Moreover, PL measurements performed on the terbium doped material show the presence of Terbium as Tb ³⁺ in the material.     

Nanoparticles size effects in thermoluminescence of oxyfluoride glass-ceramics containing Sm<Superscript>3+</Superscript>-doped CaF<Subscript>2</Subscript> nanocrystals

Oxyfluoride glass-ceramic in the system SiO₂–Al₂O₃–CaF₂–SmF₃ containing Sm³⁺-doped CaF₂ nanocrystals in the range from 15 to 150 nm size were produced by using the controlled ceramization of the precursor glass. The incorporation of the Sm³⁺-dopant ion in the glass ceramic creates new electron-trapping centers and thermoluminescence (TL) method has been used in order to trace their evolution during glass ceramization. The 370 °C TL peak observed in precursor glass has been assigned to the recombination of the electrons released from the Sm²⁺-traps in the amorphous glass network. In the glass-ceramic sample containing nanocrystals with about 15 nm size the new weak TL peaks at 270, 290, and 310 °C were attributed to the recombination of the electrons released from the Sm²⁺-traps located mainly at the surface of the CaF₂ nanocrystals. In the glass-ceramic sample containing nanocrystals with about 150 nm size, the new TL peaks at 232, 270, and 302 °C size have been assigned to the recombination of the electrons released from the Sm²⁺-traps located inside the CaF₂ nanocrystals.     

Luminescence spectra of non-stoichiometric aluminates doped with Eu2+ ions

Luminescence measurements indicate that in Al₂O₃-deficient aluminate phosphors with the magnetoplumbit crystal structure, aprt of the Eu²⁺ activator ions occur in β-alumina-type oxygen surroundings rather than in magnetoplumbite-type oxygen surroundings. In Al₂O₃-rich β-alumina type aluminate phosphors part of the Eu²⁺ ions has a magnetoplumbite-type oxygen surrounding.     

Thermoluminescence studies on Cu-doped Li2B4O7 single crystals

Lithium tetraborate (Li₂B₄O₇) is a tissue equivalent material and single crystals of this material doped with Cu are promising for dosimetric applications. In the present study highly transparent single crystals of lithium tetraborate (Li₂B₄O₇) doped with Cu (0.5 wt%) have been grown using the Czochralski technique. The Li₂B₄O₇:Cu crystals were studied using photoluminescence, X-ray diffraction (XRD), UV-vis transmission, time resolved fluorescence and thermoluminescence (TL) techniques. The TL readout of Li₂B₄O₇:Cu crystals showed two well-defined glow peaks at 402 K (peak-1) and 513 K (peak-2) for a 4 K/s heating rate. While the low temperature TL peak-1 fades completely within 24 h at room temperatures, the main dosimetric peak-2 remains the same. The TL sensitivity of the grown single crystal is found to be 3.3 times that of a conventional TL phosphor, TLD-100. The Li₂B₄O₇:Cu crystals showed a linear TL dose-response in the range from 1 mGy to 1 kGy. The TL analysis using a variable dose method revealed first order kinetics for both the peaks. Trap depth and frequency factor for peak-1 were found to be 0.81 eV and 5.2×10⁹ s⁻¹, whereas for peak-2 the values were 1.7 eV and 1.7×10¹⁶ s⁻¹, respectively.     

Photoluminescence and phosphorescence properties of MAl2O4:Eu, Dy (M=Ca, Ba, Sr) phosphors prepared at an initiating combustion temperature of 500 °C

Eu²⁺ and Dy³⁺ co-doped calcium aluminate, barium aluminate and strontium aluminate phosphors were synthesized at an initiating combustion temperature of 500 °C using urea as an organic fuel. The crystallinity of the phosphors was investigated by using X-ray diffraction (XRD) and the morphology was determined by a scanning electron microscope (SEM). The low temperature monoclinic structure for both CaAl₂O₄ and SrAl₂O₄ and the hexagonal structure of BaAl₂O₄ were observed. The effect of the host materials on the photoluminescence (PL) and phosphorescence properties were investigated by using a He-Cd Laser and a Cary Eclipse fluorescence spectrophotometer, respectively. The broad band emission spectra observed at 449 nm for CaAl₂O₄:Eu²⁺, Dy³⁺, 450 nm (with a shoulder-peak at 500 nm) for BaAl₂O₄:Eu²⁺, Dy³⁺ and 528 nm for SrAl₂O₄:Eu²⁺, Dy³⁺ are attributed to the 4f⁶5d¹ to 4f⁷ transition in the Eu²⁺ ion in the different hosts.