Thermally Stimulated Luminescence Studies Research Articles

Luminescence studies of Eu3+ doped BaGd2O4 phosphor

The spectroscopic properties of BaGd2-xO4:Eux (x = 0.0 - 0.1) phosphors were investigated. The phosphors were synthesized by conventional solid state reaction method. The samples were characterized by powder-XRD and energy dispersive spectroscopy (EDS) techniques. The photoluminescence (PL) and thermally stimulated luminescence (TSL) studies of these materials were investigated. For PL studies the samples were excited with 258 nm UV light. All the samples showed strong red emission at 611 nm due to 5D0→ 7 F2 electric dipole transition of Eu3+ ions. PL peak intensity was found to increase with increase in the dopant concentration. For TSL studies, samples were γ-irradiated with different dose rates using 60Co source. TSL of these phosphors showed a sharp glow peak with maxima at 394 K. Incorporation of europium activator in BaGd2O4 phosphor resulted in the increase of peak intensity. The trap parameters viz., order of kinetics (b), activation energy (E) and frequency factor (S) associated with the most intensive glow peak of BaGd2O4:Eu3+ phosphor were determined using glow curve shape (Chen’s) method. These phosphors can be useful in TL dosimetry Keywords: Phosphors, Photoluminescence, U.V Excitation, Thermoluminescence, Dosimetry

Luminescence Studies of Eu 3+ Doped BaGd 2 O 4 Phosphor

The spectroscopic properties of BaGd 2-x O 4 :Eu x (x = 0.0 - 0.1) phosphors were investigated. The phosphors were synthesized by conventional solid state reaction method. The samples were characterized by powder-XRD and energy dispersive spectroscopy (EDS) techniques. The photoluminescence (PL) and thermally stimulated luminescence (TSL) studies of these materials were investigated. For PL studies the samples were excited with 258 nm UV light. All the samples showed strong red emission at 611 nm due to 5 D 0 → 7 F 2 electric dipole transition of Eu 3+ ions. PL peak intensity was found to increase with increase in the dopant concentration. For TSL studies, samples were γ-irradiated with different dose rates using 60 Co source. TSL of these phosphors showed a sharp glow peak with maxima at 394 K. Incorporation of europium activator in BaGd 2 O 4 phosphor resulted in the increase of peak intensity. The trap parameters viz., order of kinetics (b), activation energy (E) and frequency factor (S) associated with the most intensive glow peak of BaGd 2 O 4 :Eu 3+ phosphor were determined using glow curve shape (Chen's) method. These phosphors can be useful in TL dosimetry.

Preparation and TSL studies in Tb activated LiMgPO4 phosphor

Abstract LiMgPO 4 :Tb 3+ phosphor was synthesized by solid state reaction. The thermally stimulated luminescence (TSL) glow curve of Tb doped LiMgPO 4 exhibits a main TSL peak at 170 °C with shoulders at 100 and 260 °C on either side of this peak. The TSL sensitivity of the phosphor was found to be about 2.5 times that of CaSO 4 :Dy phosphor. TSL emission and photoluminescence (PL) studies show that Tb 3+ ion acts as luminescence centre in this phosphor. The kinetic parameters, namely activation energy ( E ) and frequency factor ( s ) associated with the main glow peak have been determined using peak shape method. The activation energy and frequency factor obtained are 1.35 ± 0.03 eV and (6.53 ± 0.43) × 10 14 s −1 respectively. The paper discusses the dosimetric characteristics like dose response, fading, energy response and minimum detectable dose and results thereof.

Luminescence and EPR studies of YBO 3:U

Yttrium borate doped with uranium was prepared by mixing and heating yttrium oxide obtained through oxalate precipitation route, boric acid and requisite amount of nuclear-grade uranium oxide at high temperature. Photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on gamma-irradiated doped/undoped yttrium borate samples in the temperature range 300–600 K. TSL studies showed the presence of two glow peaks at 414 and 471 K. PL studies along with lifetime decay investigation suggested uranium goes in the matrix as UO 2 2+. EPR studies showed the presence of O 2 −radical ion along with electron trapped in defect centres, which might have been produced for charge compensation. Apart from this, CO 2 − radical was also observed in the system having its origin from residual oxalate ion. Temperature dependence EPR studies of the observed radical confirmed the involvement of the CO 2 − and dioxide radical ion in the observed glow peaks. By correlating the TSL, PL and ESR data, probable mechanism is proposed for the observed TSL glow in the system.

Determination of kinetic parameters of thermally stimulated luminescence of Cu-doped BaSO 4

Studies of thermally stimulated luminescence (TSL) of doped BaSO 4 with Cu activator have been carried out. The polycrystalline sample of Cu-doped BaSO 4 is prepared by recrystallisation method. The characterization and elemental analysis of BaSO 4:Cu compound are carried out by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX). The compound has orthorhombic structure at room temperature. The TSL studies of Cu-doped BaSO 4 sample show two glow peaks at 160 and 227 °C. Comparison of TL intensity of the most intensive glow peak of Cu- and Mn-doped BaSO 4 compounds with that of undoped BaSO 4 shows that addition of Cu and Mn impurity in BaSO 4 compound enhances the TL intensity by about 9 and 3 times, respectively. Among the studied samples, namely undoped, Cu- and Mn-doped BaSO 4, Cu-doped BaSO 4 is found to be the most sensitive. The trap parameters namely order of kinetics ( b), activation energy ( E), frequency factor ( s) and Balarin parameter ( γ) associated with the most intensive glow peak, i.e. the 227 °C glow peak of BaSO 4:Cu phosphor were determined by using isothermal decay method and glow curve shape (Chen's) method and these parameters are in good agreement.

Thermally stimulated luminescence and electron paramagnetic resonance studies of Eu3+-doped yttrium borate

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on gamma-irradiated europium-doped yttrium borate samples in the temperature range 300–600 K. TSL studies showed the presence of two glow peaks, a relatively weaker one at 390 K and an intense one at around 550 K. Room-temperature EPR spectrum of irradiated samples revealed the formation of two hole trapped radicals, namely, BO32− and O2−. Temperature variation studies showed drastic reduction in the EPR signal intensities of these radicals around 390 and 550 K indicating thermal destruction of O2− and BO32− radicals, respectively. The observed TSL emission is caused by the recombination of thermally released holes from O2− and BO32− radical ions with electrons. The energy released in electron-hole recombination process is used for the excitation of Eu3+ ion resulting in TSL glow peaks. TSL emission studies confirmed that Eu3+ acts as luminescent center for both the peaks.

EPR and TSL studies on MgB 4O 7 doped with Tm: role of BO 32− in TSL glow peak at 470 K

Electron paramagnetic resonance (EPR), thermally stimulated luminescence (TSL), photoacoustic spectrometric (PAS) and fluorescence studies were conducted on gamma-irradiated MgB 4O 7: Tm phosphor. EPR spectra of irradiated samples revealed the formation of BO 3 2 - , 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 3 2 - radical around 470 K. The observed TSL emission is caused by the recombination of thermally released holes from BO 3 2 - 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.

Evaluation of trapping parameters of thermally stimulated luminescence glow curves in Cu-doped Li 2B 4O 7 phosphor

Evaluation of trapping parameters, including order of kinetics, activation energy and frequency factor, is one of the most important aspect of studies in the field of thermally stimulated luminescence (TSL). A polycrystalline sample of Cu-doped Li 2B 4O 7 was prepared by the melting method. Formation of the doped compound was checked by use of Fourier-transform infrared (FTIR) spectroscopy. TSL studies of the Cu-doped lithium tetraborate sample shows three glow peaks, the maximum emission occurring, respectively, at a temperature of 175°C, 290°C and 350°C, the intensity of the 175°C-glow peak being the maximum. The trapping parameters associated with this prominent glow peak of Cu-doped lithium tetraborate are reported herein, using the isothermal luminescence decay and glow curve shape (Chen's) methods. Our results show very good agreement between the trapping parameters calculated by the two methods.

TSL and EPR studies of SrBPO5 doped with CeO2and co-doped with CeO2 and Sm2O3

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO5 samples doped with CeO2 and co-doped with CeO2 and Sm2O3. On gamma-irradiation at room temperature, BO32-, O2- and O- radicals were produced. It was seen that the O- radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O- radical ions results in transfer of recombination energy to the impurity centre Ce3+ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce3+ to Sm3+ resulting in increase in the intensity of glow peak at 485 K.

Radiation effect on the luminescence of LiYF 4:Er 3+

Luminescence and also the effects of ionising radiation on luminescence have been investigated in LiYF 4:Er. The defects created by ionising radiation are studied by means of Thermally Stimulated Luminescence (TSL) and Electron Spin Resonance (ESR). TSL studies indicate a prominent glow peak at 386–412 K, whose position is found to depend on the radiation dose. Two defect centres, tentatively assigned to F-centres, are observed at room temperature. Step annealing measurements suggest a connection between these centres and the TSL glow peak. Photoluminescence studies indicate considerable reduction in emission intensity which appears to arise from the distortion of the lattice around the Er 3+ ion caused by the defect centres. An explanation of the observations is suggested on the basis of impurity ion-defect centre formation.

Radiation stabilization of U5+ in CaO matrix and its thermal stability: Electron paramagnetic resonance and thermally stimulated luminescence studies

Electron paramagnetic resonance (EPR) evidence is presented for the radiation stabilization of pentavalent uranium in CaO matrix. From the theoretical predictions ofg value for U5+ in axial symmetries, it was concluded that U5+ at Ca2+ site is associated with a second neighbour charge compensating Ca2+ vacancy. EPR measurements also revealed the presence of Mn2+, Mn4+ and Cu2+ impurities in the samples. The thermal stability of U5+ was investigated using EPR and thermally stimulated luminescence (TSL) techniques. The TSL and EPR studies on gamma irradiated uranium doped calcium oxide samples had shown that the intense glow peak at 540 K is associated with the reduction in the intensity of EPR signal of U5+ ion around this temperature. This peak is associated with the process U5++hole→U6+*→U6++hv. The activation energy for this process was determined to be 1.4eV.

Internal irradiation effects in239Pu doped K2Ca2(SO4)3): EPR, TSL and PAS investigations

The electron/hole trapped centres created during internal irradiation in239Pu doped K2Ca2(SO4)3 were investigated using electron paramagnetic resonance (EPR), thermally stimulated luminescence (TSL) and photoacoustic spectroscopic studies (PAS). These techniques were used to identify the defects and characterize the thermally induced relaxation processes. TSL studies of self (α)/γ-irradiated239Pu doped K2Ca2(SO4)3 revealed two glow peaks around 400 and 433K. Plutonium introduced as Pu4+ was partly reduced to Pu3+ due to self irradiation. This was ascertained from PAS studies. EPR studies carried out on these samples showed the formation of radical ions SO 4 − , SO 3 − , O 3 − , etc. The thermal destruction of SO 4 − ion was found to be associated with the prominent glow peak around 433K. Pu3+ was found to act as luminescent centre for the observed TSL glow. The trap depth for the glow peak at 433K has been determined from TSL and EPR data.

Thermally stimulated luminescence studies of a LiYF4:U4+ crystal

The present paper gives the first detailed report on trap level spectroscopic studies of gamma irradiated lithium-yttrium tetrafluoride single crystals doped with tetravalent natural uranium. The work carried out includes the growth of single crystals followed by thermally stimulated luminescence (TSL) and electron spin resonance (ESR) studies on the gamma irradiated crystal. The TSL studies in the 300–600 K temperature range have revealed the presence of four glow-peaks. The trap parameters have been calculated for the two prominent peaks. The predominant radiation-induced colour centre has been identified as an F centre and its growth and annihilation behaviour has been studied in detail. ESR studies on the gamma irradiated crystal at 300 K have shown formation of U 5+ ions in small amounts. Further, the spectral character of the glow-peaks revealed the presence of a strong emission group at 690 nm, characteristic of tetravalent uranium ions. It has been suggested that U 4+ ions play an important role in TSL, taking part in the (U 4+ →U 5+ ) process.

Charge trapping and luminescence in biochemical systems

A review of radiation-induced charge trapping and release in biochemical systems is given. Several techniques appropriate to studying this damage are discussed; electron spin resonance (ESR), electron-nuclear double resonance (ENDOR), optical absorption, muon spin rotation (μSR), and thermally stimulated luminescence (TSL), for example, with the emphasis being on TSL. Experimental aspects of this technique, along with many results from TSL studies of amino acids, proteins, DNA, RNA, and related compounds are reviewed. Specific models derived from analyses of the TSL glow curves and emission spectra are discussed. The overwhelming majority of these studies suggest that electronic deexcitation of the radiation-induced trapped charge occurs via the singlet and triplet manifolds of the molecule.