Role of defect centres in thermoluminescence mechanism of Tb 3+ doped MgAl 2 O 4 (original) (raw)
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Effect of the Fuels on the Luminescence Characterisation of Tb Doped MgAl 2O4 Phosphors
2013
There are number of factors beside the physical state of the sample, the nature of excitation radiation and types of the impurity ions in a phosphor. Less attention has been paid to the effect of fuels on host preparation in its final performance. Tb(0.5mol%) doped MgAl 2O4 phosphors have been synthesised by solution combustion technique by using different fuel like carbohydrazide, hydrazine and urea and their photoluminescence (PL), thermoluminescence (TL) and mechanoluminescence (ML) properties have been studied. XRD result confirms formation of the phosphor. ML has been excited impulsively by dropping a load of mass 0.7 kg on to the phosphors from various heights. As the piston is dropped on to the sample, ML intensity initially increased with time attained an optimum value for a particular time then decreased again increases to a value than decreases and finally disappeared for all the samples. ML intensity increased with gamma doses given to the sample. PL emission spectrum sho...
Cumhuriyet Science Journal, 2021
In this study, undoped MgO and titanium (Ti4+) doped MgO ceramics were synthesized using the solid state-assisted solution combustion synthesis method. The structural characteristics were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). TL curves of the MgO:Ti4+(0.1%wt) ceramic consist of three TL peaks located at 70, 250 and 290 oC with a heating rate of 2 oC/s after 1 Gy beta dose. Radioluminescence (RL) characteristic of the MgO:Ti4+(0.1%wt) ceramic was studied with excitations between 200 - 1000 nm. It was found to be the four emission bands the maximums located at 327 nm (~3.79 eV), 694 nm (~1.78 eV), 715 (~1.73 eV), and 745 (~1.66 eV). Some dosimetric characteristics such as TL curve, reusability, dose-response, of the ceramic were investigated using the thermoluminescence (TL) technique using beta radiation of 90Sr/90Y. Dose-response characteristics showed the integrated TL signals between 170-350 oC exhibited a linear up to 20 Gy. The experi...
Luminescence of Ce doped MgAl2O4 prepared by the combustion method
Physica B: Condensed Matter, 2014
Magnesium aluminate (MgAl 2 O 4) has received special attention as a technologically important material because of its attractive properties, such as mechanical strength, chemical inertness, a wideband gap, relatively low density, high melting point, high thermal shock resistance, low thermal expansion coefficient, resistance to neutron irradiation and low dielectric loss. It has also been used as a phosphor host activated by a variety of transition metal and lanthanide ions. A simple combustion method was employed for the preparation of Ce doped MgAl 2 O 4 nanocrystals using metal nitrates as precursors and urea as a fuel in a preheated furnace at 520 1C. The as-prepared samples were annealed in a hydrogen atmosphere to improve their optical properties. The samples thus obtained were characterized by X-ray diffraction (XRD), UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and photoluminescence spectroscopy (PL). The XRD data showed that all the samples had the spinel structure and the average particle size of the as-prepared samples was about 25 nm. PL spectra of Ce doped MgAl 2 O 4 using an excitation wavelength of 350 nm produced broad green emission bands centred at 500 nm. Maximum green emission was obtained for the sample doped with 0.75 mol% Ce. UV-vis diffuse reflectance spectra and XPS were used to obtain more information on the conversion of Ce ions from the non-luminescent Ce 4 þ to the luminescent Ce 3 þ charge state.
Geochronometria
The present study aimed at quantifying the relationship between TL and either CW-OSL or LM-OSL using commercially available magnesium oxide. The samples were bleached at two different temperatures, and a component-resolved analysis on the integrated signals was performed. According to the data of the present study, each one among the five observed LM-OSL component receives electrons from at least two different TL peaks. Two different fast OSL components were resolved in the LM-OSL curves, both accumulating electrons from all TL glow peaks with Tmax>150°C. Component C 3 is very well correlated with the TL peaks at 102, 135 and 194°C, while components C4 and C 5 are related to the TL glow peaks of 292°C, 353°C and 464°C. We note that for CW-OSL the resolution is good when two or more components differ in intensity by an order of magnitude. Blue stimulation depletes substantially the first two TL peaks but not the third peak. Substantial depletion of the high-temperature TL peaks is...
Mechanoluminescence and thermoluminescence of Tb in CaAl 2 O 4 prepared by a solution combustion method has been reported. Phase purity, formation of a phosphor and surface morphology were confirmed by XRD and SEM techniques. The resulting phosphors were characterized by photoluminescence (PL) to detect incorporation of the dopant. When a gamma-irradiated Tb-doped CaAl 2 O 4 crystal is impulsively deformed, two peaks appear in the ML intensity versus time curve, whereby the first ML peak is found in the deformation region and the second in the post deformation region of the crystals. The energy levels and hence trapping and detrapping mechanism of charge carriers can be explained using ML. The Tbdoped CaAl 2 O 4 phosphor can be used in the dosimetric applications for ionizing radiation. The TL characteristics of CaAl 2 O 4 may be useful for high radiation doses. Thermoluminescence (TL) materials have wide applications in the dosimetry of ionizing radiation, scintillators, X-ray laser materials, etc. The samples were irradiated using a 60 Co gamma-ray source at a dose of 0.930 kGy h À1 and the heating rate used for TL measurements was 5 C s À1. The samples show good TL peaks for 0.2 mol% (urea), 0.2 mol% (hydrazine) and 0.2 mol% (carbohydrazide) doping concentrations of Tb 3+ ions. We also report a more detailed theoretical understanding of the mechanism of TL and ML. All TL glow curves obey the secondorder kinetics with a single glow peak, which reveals that only one set of trapping parameters is set for a particular temperature. The TL sensitivity was found to depend upon the annealing temperature and Tb 3+ doping concentration. The prepared sample may be useful in TL dosimetry.
EPR and TSL studies on MgB4O7 doped with Tm: role of BO32− in TSL glow peak at 470K
Radiation Measurements, 2005
Electron paramagnetic resonance (EPR), thermally stimulated luminescence (TSL), photoacoustic spectrometric (PAS) and fluorescence studies were conducted on gamma-irradiated MgB 4 O 7 : Tm phosphor. EPR spectra of irradiated samples revealed the formation of BO 2− 3 , a hole-trapped radical at room temperature. The principal values for the g and A tensors are g ≈ 2.0071, g ⊥ = 2.0131 and A ≈ 14 G, A ⊥ = 7 G, respectively. In addition to this, the radical without any hyperfine structure was identified as O − 2 (g = 2.0385 and g ⊥ = 2.0023). TSL studies showed the presence of an intense glow peak around 470 K and a weak shoulder at 550 K. Temperature dependence studies of the EPR signals in the range 300-600 K showed the thermal destruction of BO 2− 3 radical around 470 K. The observed TSL emission is caused by the recombination of thermally released holes from BO 2− 3 radical with Tm 2+ ion. The energy released in the electron-hole recombination process is used for the excitation of Tm 3+ resulting in a prominent glow 470 K. TSL emission studies confirmed that Tm 3+ acts as luminescent center for the prominent peak at 470 K. The trap depth for this peak has been determined to be 0.975 ± 0.03 eV from both TSL and EPR methods.
Effects of Ta doping and irradiation with He+ ions on photoluminescence of MgAl2O4 spinel ceramics
Journal of the European Ceramic Society, 2020
Photoluminescence (PL) properties of pristine and Ta-doped MgAl 2 O 4 spinel ceramics prepared via spark plasma sintering technique and irradiated with He + ions were studied. The results indicate strong influence of the grain boundaries on PL spectra. Ta doping promotes the formation of O and Al vacancies at the grain boundaries leading to an increased number density of F + centres. The ionised irradiation forms antisites preferentially at the grain boundaries, which inhibit excitonic PL and exciton energy transfer while do not affect proper PL of lattice defects. A weak PL excitation band at 7.25±0.25 eV may belong to excitons localised near bulk antisites. In the Ta-doped ceramics, the electronic transitions between 5.75 eV and 7.0 eV belong to an intermediate state situated at the grain boundaries and structurally linked to Ta, which readily transfers energy to F and F + centres; it was assigned to the nucleated Mg 4 Ta 2 O 9 phase.
Physica B: Condensed Matter, 2020
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Thermoluminescence properties of Tb doped Mg2SiO4 after beta irradiation
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2019
In this study, we performed Thermoluminescence (TL) experiments to extract the trapping parameters and dosimetric properties of Tb-doped Mg 2 SiO 4 phosphors. Glow peaks located at 193, 270, and 350°C were observed in the glow curve but the peak at 193°C was especially investigated as a dosimetric peak in this study. We also observed an anomalous heating rate effect in which the maximum TL intensity of the glow curve augmented with an increasing heating rate. The computerized glow curve deconvolution (CGCD) method, initial rise (IR) and Hoogenstraaten's method were used to determine the activation energies of associated trapping centers for both BSL-TL 365 nm and IRSL-TL wideband blue filters. The TL characteristics of this phosphor indicate that Mg 2 SiO 4 :Tb 3+ could be a promising material for dosimetric applications. Efforts should be made to improve the fading behaviour by adding other activators as co-dopants.