Thermally Stimulated Luminescence Glow Peak Research Articles

Synthesis, characterization, photoluminescence and thermally stimulated luminescence investigations of orange red-emitting Sm3+-doped ZnAl2O4 phosphor

Sm3+-doped ZnAl2O4 phosphor was synthesized by citrate sol-gel method and characterized using X-ray diffraction and scanning electron microscopy to identify the crystalline phase and determine the particle size. Photoluminescence (PL) studies on the sample showed emission peaks at 563, 601, 646 and 707 nm with λ ex = 230 nm corresponding to the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions, respectively, due to Sm3+ ions. PL lifetime decay studies confirmed that Sm3+ ions partly entered into the lattice by replacing Al3+ ions and remaining located at the surface of ZnAl2O4 host matrix. Thermally stimulated luminescence (TSL) studies of γ-irradiated Sm3+-doped ZnAl2O4 sample showed two glow peaks at 440 and 495 K, the former being most intense than the latter. The trap parameters were determined using different heating rate methods. Spectral characteristics of the TSL glow showed emission around 565, 599 and 641 nm, indicating the role of Sm3+ ion as the luminescent centre. A probable mechanism for the prominent TSL glow peak, observed at 440 K, was proposed. CIE chromaticity coordinates for the system was evaluated, which suggested that Sm3+-doped ZnAl2O4 could be employed as a potential orange red-emitting phosphor.

Optical properties of sol–gel derived Sr2SiO4:Dy3+ – Photo and thermally stimulated luminescence

Trivalent dysprosium-doped strontium silicate (Sr2SiO4) phosphors were prepared by sol–gel synthesis using tetra ethyl orthosilicate (TEOS) as precursor. The synthesis temperature could be brought down to 600°C for formation of a single phase sample. The material was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), photoluminescence (PL), and thermally stimulated luminescence (TSL). The luminescence study revealed strong 4F9/2→6H13/2 transition at 577nm (yellow), strong 4F9/2→6H15/2 transition at 482nm (blue) and weak 4F9/2→6H11/2 transition at 677nm (red), when excited by 250nm (Charge transfer band, CTB) or 352nm (f–f band). The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Dy3+ ions was evaluated based on which, the quenching mechanism was verified to be a multipole–multipole interaction. The thermally stimulated luminescence studies of Sr2SiO4:Dy3+ sample showed main TSL glow peak at 413K. The trap parameters namely activation energy (E), order of kinetics (b), and frequency factor (s) for this peak were determined using glow curve shape method.

Deep trapping states in cerium doped (Lu,Y,Gd)3(Ga,Al)5O12 single crystal scintillators

We study deep trapping states in Ce3+-doped garnet crystals with the composition (Lu,Y,Gd)3(Ga,Al)5O12, recently shown as having remarkably high light yield. We use thermally stimulated luminescence (TSL) technique above room temperature and determine the composition Gd3Ga3Al2O12 as the host showing the lowest concentration of traps. This host consistently manifests very low afterglow comparable to that of the standard BGO crystal. We also perform TSL glow peak analysis based on the initial rise technique to evaluate trap depth and other characteristics associated with TSL peaks.

Thermally Stimulated Luminescence in Ce-Doped Yttrium Oxyorthosilicate

We analyze thermally stimulated luminescence (TSL) above room temperature in Ce-doped Y2SiO5 oxyorthosilicate single crystal. We perform detailed TSL glow peak analysis based on the initial rise technique to evaluate trap depths and other characteristics associated with TSL peaks. The tunneling process previously proposed to be at work in recombination mechanism of Ce-doped lutetium oxyothosilicate was not confirmed in presently studied isostructural yttrium silicate. The charge carrier transfer between traps and Ce recombination centers is rather accomplished via conduction band.

Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance investigations of Tb 3+ doped SrBPO 5

Trap level spectroscopic studies were carried out on γ-irradiated Tb (1 mole%) doped SrBPO 5 were carried out using photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) techniques. The incorporation of Tb in the 3+ oxidation state was ascertained from PL studies. Life time for Tb 3+ emission corresponding to the intense transition 5D 4 → 7F 5 at 543 nm was determined. The spectral characteristics of the TSL glows have shown that Tb 3+ ions act as the emission center for the glow peak at 475 K. The trap parameters of the glow peak were determined. EPR investigations at room temperature/77 K revealed the stabilization of three boron oxygen hole trapped centers (BOHC's) and oxygen centered radicals such as O − and O 2 − and trapped electrons in room temperature γ-irradiated samples. TSL glow peak at 475 K was found to be associated with recombination of electron released from trapped electron center and the BOHC 2 center.

Effect of Eu and Pb doping on the dosimetric properties of LiCAF

LiCaAlF6 (LiCAF) crystals doped with two different ions (europium and lead) have been investigated as potential new dosimetric materials. The stability of thermally stimulated luminescence (TSL) glow peaks in LiCAF:Eu was evaluated by means of the initial rise technique. The decay times at room temperature of the traps related to the dosimetric glow peaks were found to range between 40 and 2 × 104 years confirming the good dosimetric characteristics of this crystal. The glow curve of LiCAF:Pb is dominated by a peak at approximately 300 °C emitting in the UV region (3P0,1–1S0 transition of Pb2+) superimposed to a very broad structure at lower temperature (20–200 °C) featuring recombination at an intrinsic defect centre. The anomalous behavior of the low temperature structure during thermal cleaning procedures prevented any reliable numerical analysis of the TSL glow peak at 300 °C.

Study of kinetic parameters of K 2Ca 2(SO 4)3 thermoluminescence dosimeter

The dosimetry study of thermoluminescence materials is based on a good knowledge of its kinetics para-meters. A polycrystalline sample of K 2Ca 2(SO 4)3 was prepared by the solid-state diffusion method. Formation of the compound was checked by using X-ray diffraction and Fourier-transform infrared spectroscopy. Thermally stimulated luminescence (TSL) glow curves of X-ray-irradiated K 2Ca 2(SO 4)3 phosphor exhibit one glow peak at 195 °C and a shoulder at around 120 °C, indicating that two different sets of traps are being activated within the particular temperature range, each with its own value of activation energy (E) and frequency factor (s). The kinetic parameters associated with the prominent glow peak of K 2Ca 2(SO 4)3 were calculated using the isothermal luminescence decay method. The electron spin resonance study of the prepared compound exhibits the presence of and radical ions that are responsible for the observed TSL glow peaks. The release of hole/electron from trap centres at the characteristic trap site initiates the luminescence process in these materials.

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.

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.

Studies of defects in YVO4:Pb2+, Eu3+ red phosphor material

Doubly doped YVO 4 :Pb 2+ , Eu 3+ red phosphor materials with fixed Eu 3+ concentration (5 mol%) and varying Pb 2+ concentration were prepared via a self-propagating (combustion) synthesis. This consisted of bringing a saturated aqueous solution of the desired metal salts and a suitable organic fuel to the boil, until the mixture ignited and a self-sustaining and rather fast combustion reaction initiated, resulting in dry, amorphous or usually crystalline fine particles of the desired material. The formation of crystalline vanadates was confirmed by X-ray diffraction. A strong emission line at 619 nm due to the 5 D 0 → 7 F 2 transition in the red region was observed. Defects, created by gamma radiation, were studied by means of photoluminescence, thermally stimulated luminescence (TSL) and electron spin resonance. Photoluminescence studies display considerable reduction in emission intensity which appears to arise due to the formation of defect centres after irradiation. The defect centres formed in the present system are tentatively assigned to F + centres and step annealing measurements suggest a connection between these centres and the TSL glow peak.

Electron paramagnetic resonance, photo-acoustic spectroscopy and thermally stimulated luminescence for identification of thermally stimulated processes in gamma-irradiated LaBa2F7

Abstract Thermally stimulated luminescence (TSL), electron paramagnetic resonance (EPR) and photo-acoustic spectroscopy (PAS) techniques were used to investigate the radiation induced centers in polycrystalline LaBa2F7 containing trace amounts of other rare-earths particularly Gd3+ and Sm3+. The TSL glow curve of LaBa2F7 after g-irradiation to a dose of 3 kGy had shown a weak TSL glow peak at 390 K and a much stronger one at 495 K. The EPR spectra of the g-irradiated LaBa2F7 samples showed the presence of O- and O2 - ions. Temperature dependence study of the EPR spectra showed that the thermal destruction of O- ion occurs in the 460-490 K temperature range. In g-irradiated samples, O- and F-centers were identified by PAS. The correlation of EPR and PAS results indicate that the prominent TSL glow at 495 K is associated with the thermal destruction of O- radical ion. The trap parameters viz. trap depth and frequency factor have been determined from TSL data.

Luminescence characterization of titanium related defects in 6H–SiC

Photoluminescence (PL), thermally stimulated luminescence (TSL) and their photo-excitation spectra in hexagonal type SiC were studied between the temperatures of 5 and 300 K. Titanium related TSL glow peak is observed close to 140 K in compensated crystals 6H–SiC with corresponding thermal ionisation energy of a trap close to 170 meV. The spectral distribution of TSL has a maximum at 1.8 eV in 6H–SiC and 2.43 eV in 4H–SiC. A specific structure in the photo-excitation spectrum of PL close to the exciton gap E gx=3.023 eV is revealed, exclusively in 6H–SiC material. This indicates an essential role of excitons in the resonance energy transfer to the Ti-related centers in silicon carbide. The results are discussed in a model of isoelectronic centers composed of either individual Ti atoms or Ti–N pair representing a complex of the electronic trap and recombination center.

PhotoinducedPb+center inPbWO4:Electron spin resonance and thermally stimulated luminescence study

Electron traps based on regular Pb sites perturbed by oxygen vacancies ${(V}_{\mathrm{O}})$ in high purity undoped ${\mathrm{PbWO}}_{4}$ have been revealed and studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL) measurements. Detailed analysis of ESR spectra parameters $(g$ factor, hyperfine, and superhyperfine structures) along with the variation of the concentration after annealing in inert and oxygen atmospheres had shown that revealed centers are ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ complexes. The ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers are created in two ways: (i) by direct trapping of the electrons from the conduction band under x-ray or ultraviolet irradiation at $T=60 \mathrm{K};$ (ii) by retrapping of electrons freed from unperturbed $({\mathrm{WO}}_{4}{)}^{3\ensuremath{-}}$ centers after irradiation at $T<40 \mathrm{K},$ followed by heating at $T=60 \mathrm{K}.$ Above $T\ensuremath{\approx}180 \mathrm{K},$ ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers are thermally ionized, giving rise to a TSL glow peak due to the recombination of freed electrons with localized holes. The emission spectrum of the TSL features one band peaking at around $2.5 \mathrm{eV}.$ The temperature dependence of both TSL and ESR intensities has been analyzed using a first order recombination model: the thermal ionization energy of ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers turns out to be $0.55 \mathrm{eV}.$ The role of ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers in the processes of carrier trapping and recombination of nonequilibrium carriers in the ${\mathrm{PbWO}}_{4}$ lattice is briefly discussed.

Photoinduced(WO4)3−−La3+center inPbWO4:Electron spin resonance and thermally stimulated luminescence study

Electron traps based on regular Pb sites perturbed by oxygen vacancies ${(V}_{\mathrm{O}})$ in high purity undoped ${\mathrm{PbWO}}_{4}$ have been revealed and studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL) measurements. Detailed analysis of ESR spectra parameters $(g$ factor, hyperfine, and superhyperfine structures) along with the variation of the concentration after annealing in inert and oxygen atmospheres had shown that revealed centers are ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ complexes. The ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers are created in two ways: (i) by direct trapping of the electrons from the conduction band under x-ray or ultraviolet irradiation at $T=60 \mathrm{K};$ (ii) by retrapping of electrons freed from unperturbed $({\mathrm{WO}}_{4}{)}^{3\ensuremath{-}}$ centers after irradiation at $Tl40 \mathrm{K},$ followed by heating at $T=60 \mathrm{K}.$ Above $T\ensuremath{\approx}180 \mathrm{K},$ ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers are thermally ionized, giving rise to a TSL glow peak due to the recombination of freed electrons with localized holes. The emission spectrum of the TSL features one band peaking at around $2.5 \mathrm{eV}.$ The temperature dependence of both TSL and ESR intensities has been analyzed using a first order recombination model: the thermal ionization energy of ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers turns out to be $0.55 \mathrm{eV}.$ The role of ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers in the processes of carrier trapping and recombination of nonequilibrium carriers in the ${\mathrm{PbWO}}_{4}$ lattice is briefly discussed.

Electron traps in the scintillator material PbWO4 and their correlation to thermally stimulated luminescence

Various efforts to improve radiation hardness and scintillation properties of lead tungstate with respect to its application in high energy calorimeters by doping with suitable ions like Nb, La, Gd or Lu have been checked for their success mainly by studying optical absorption and thermally stimulated luminescence (TSL) after irradiation at room temperature, in a few cases at liquid nitrogen temperature. Very shallow traps, which contribute to fast scintillation processes, are not stabilized under such conditions. Extending the temperature range for irradiation as well as for experimental studies down to liquid helium temperature, we found new TSL glow peaks and established a correlation to electrons captured by anionic WO4 complexes. Their electron spin resonsnance (ESR) data together with other experimental results like temperature dependence of photoconductivity give distinct hints with respect to the energy level scheme of PbWO4.

Trap spectroscopy and tunnelling luminescence in feldspars

Comparative studies of tunnel luminescence, thermally stimulated luminescence (TSL), and trap energy spectra by the fractional glow technique (FGT) have been made both with sanidine and microcline feldspars. After X-irradiation at LNT these feldspars show intense tunnelling afterglow. As the temperature is raised, several TSL glow peaks may be observed, starting at 135K. An intense peak at 250K is common to all four investigated microclines. In samples of sanidine, tunnelling afterglow overcomes TSL up to 250–260K. With sanidine and microcline samples, the distributions of trap activation energies vs temperature obtained by the FGT are continuous and quasi-linear. Maxima in the trap density are observed, indicating the presence of several kinds of stable defect structures. It may be concluded that below 100K the thermally stimulated processes in the samples are frozen. Tunnelling recombination occurs between deeper localized states which are stable up to RT and higher. These results are attributed to the known ‘Al-Si order–disorder’ effect in feldspar crystals. It leads to the formation of wide continuous energy distributions of localized states. Donor–acceptor defects are caused by the association of Al3+ substituted in the centers of SiO4 tetrahedra and alkali ions in interstitial positions.

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 induced thermally stimulated luminescence and conductivity in SIMOX oxides

Thermally Stimulated Luminescence (TSL) and Conductivity (TSC) induced by X-ray irradiation in SIMOX buried oxides have been studied from room temperature up to 400/spl deg/C. The characteristics of an X-ray induced TSL glow peak detected around 62/spl deg/C are presented: specifically, results on the emission wavelength and trap depth are shown. The X-ray induced TSC, observed at approximately 70/spl deg/C, is due to the same trapped species responsible of the TSL emission. The stability after irradiation and dose dependence of both TSL and TSC signals have also been investigated. The results have been compared with similar studies on high temperature annealed thermal SiO/sub 2/ films and bulk materials.

Thermally stimulated free radical reactions in BaCO 3: 241Am:EPR and TSL investigations

Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) studies have been carried out in sub-room temperature region in γ-irradiated BaCO 3: 241 Am phosphor. CO - 2 and CO - 3 radical ions are found to get stabilised at 77 K. Whereas CO - 2 radical was found to be stable upto room temperature. CO - 3 was found to get destroyed around 170 K coinciding with the occurrence of a TSL glow peak at that temperature.