Thermally Stimulated Luminescence Peak Research Articles

Electron and hole traps in X-ray irradiated Y2 SiO5 and Lu2 SiO5 crystals

Characteristics of thermally stimulated luminescence (TSL) are studied for the X-ray irradiated at 4, 80, or 295 K nominally undoped Y2SiO5 and Lu2SiO5 single crystals of different origin, containing traps for holes (Ce3+, Tb3+ ions) and electrons (Eu3+, Mo6+ ions), as well as for the Sm3+-doped Lu2SiO5 crystal. For the first time, the TSL glow curves of these materials are measured separately for the electron (Ce3+-, Tb3+-related) and hole (Sm3+-, Eu3+-related) recombination luminescence. Owing to that, the TSL peaks, arising from thermal destruction of electron centers and hole centers, are separately identified. For some TSL peaks, thermal stability parameters of the corresponding traps are calculated. The results are compared with those obtained for Ce3+-doped Y2SiO5 and Lu2SiO5 crystals.

Spectral and kinetic features of thermoluminescence in hexagonal boron nitride powder after UV-irradiation

Abstract Thermally stimulated luminescence (TL) from UV-irradiated h-BN powder synthesized using carbamide technique was studied. Three TL peaks at Tmax = 380, 500 and 600 K during linear heating with 2 K/s rate in RT – 773 K temperature range were observed. It was found that the 2.90 and 3.25 eV emission bands, which were related with recombination centers on the basis of VN and BO−-complexes, dominate in TL spectra of h-BN. Experimental TL glow curves were analyzed in terms of general order kinetics and energy parameters of responsible capture levels were estimated. It was shown, considering the independent data on the luminescent properties of hexagonal boron nitride in different structural states, that TL peaks at 380 K and 600 K were due to traps based on the one-boron and the three-boron centers with thermal depth EA = 0.7 and 1.0 eV, respectively. The possible origin of the trap with EA = 1.6 eV, responsible for the TL peak at 500 K, is discussed.

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.

Photoluminescence and Afterglow Behavior of Eu<sup>2+</sup>, Dy<sup>3+</sup> and Eu<sup>2+</sup>, Sm<sup>3+</sup> in Sr<sub>3</sub>Al<sub>2</sub>O<sub>6</sub> Matrix

The long afterglow luminescent materials Sr3Al2O6: Eu, Sm and Sr3Al2O6: Eu, Dy (denoted as S1 and S2, respectively) were synthesized via solid-state reaction. X-ray diffraction, fluorescence spectrophotometer and thermal luminescent spectroscope were employed to characterize the phosphors. The excitation spectra are all well simulated by eight Gaussian curves, indicating that they originate from the 4f7(8S7/2)–4f65d(8HJ) transitions of Eu2+. The excitation spectra intensity of S1 is much stronger than that of S2, which indicates that there is a more efficient energy transfers from Sm3+to Eu2+. The thermally stimulated luminescence (TSL) curve can be fitted to four TSL peaks and the low-temperature TSL peak is responsible for the long lasting phosphorescence. The proposed explanation for the afterglow property is discussed.

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.

Site occupancy and mechanisms of thermally stimulated luminescence in Ca9Ln(PO4)7 (Ln = lanthanide)

The structural properties, X-ray-excited radioluminescence and thermally stimulated luminescence (TSL) of Ca9Ln(PO4)7 (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were investigated. (La–Nd) occupied mainly the largest M3 site, whereas the smallest lanthanides (Yb, Lu) adopted the smallest octahedral M5 site. The intermediate-sized ions (Sm–Tm) occupied the medium-sized sites M1 and M2. Only the Ln3+ ions with the highest Ln3+/4+ ionization energy (Ln=Pr, Nd, Tb, Dy) were able to trap holes and become luminescent centers for thermally stimulated Ln3+ 4f–4f emission. For low Ln3+/4+ ionization potential (Ln=La, Gd, Yb, Lu), no hole trapping at Ln3+ was possible and Mn2+ impurities at the M5 sites were the effective hole traps and luminescent centers for thermally stimulated Mn2+ 3d–3d red emission. Very broad TSL peaks were attributed to thermally assisted detrapping of electrons from positive traps, possibly Ln3+ at Ca2+ sites, tunneling back towards the hole trap/luminescent center. Ca9Ln(PO4)7 compounds doped with Ln=Tb or Lu were found to be efficient X-ray-excited long-lasting phosphorescence materials, emitting in the green and in the red, respectively.

Lead‐vacancy‐related hole centers in lead tungstate crystals

AbstractAfter UV irradiation of PbWO4 crystals at T > 140 K in the energy range around 4.05 eV, besides the thermally stimulated luminescence (TSL) peak at ≈193 K arising from electron {Pb+ − VO} centers, a TSL peak at about 225 K appears. We suggest that this ≈225 K TSL peak arises from the thermal destruction of non‐paramagnetic hole centers of the {VPb + 2h}‐type (two holes trapped at the oxygen ions in the vicinity of a single lead vacancy VPb). The recombination of thermally or optically released electrons with these hole centers at T > 140 K is accompanied with green G(II) emission peaking at about 2.5 eV. The processes of photo‐thermally stimulated creation of VPb‐related hole centers have been studied.

Effect on thermoluminescence parameters of biotite mineral due to thermal quenching

The Thermally Stimulated Luminescence (TSL) at room temperature X-ray irradiated natural biotite in form of micro-grain powder was studied under various heating rates. TSL peaks showed at temperatures 393K, 399.6K, 403.5K, 404.5K, 406.9K at their respective heating rates 2K/s, 4K/s, 6K/s, 8K/s and 10K/s. The effect of thermal quenching on thermoluminescence parameters such as peak maximum temperature, peak area, FWHM, geometrical symmetry factor, the activation energy were investigated. From the symmetry factor it is clear that the TL glow curve follows the first order kinetics for the lowest heating rate, but as the heating rate increases it defers from the first order. The activation energies for each heating rates were calculated by using Chen peak shape methods for general order kinetics and found to be decreased for higher heating rates. When activation energy is calculated by variable heating rate method it is observed that the method overestimated the value of activation energy and pre-exponential frequency factor significantly due to thermal quenching.

Synthesis, characterization, optical absorption, luminescence and defect centres in Er3+ and Yb3+ co-doped MgAl2O4 phosphors

The Er3+–Yb3+ co-doped MgAl2O4 phosphor powders have been prepared by the combustion method. The phosphor powders are well characterized by X-ray diffraction (XRD) and energy dispersive (EDX) techniques. The absorption spectrum of Er3+/Er3+–Yb3+ doped/co-doped phosphor powder has been recorded in the UV–Vis–NIR region of the electro-magnetic spectrum. The evidence for indirect pumping under 980 nm excitation of Er3+ from Yb3+ was observed in the MgAl2O4 matrix material. Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the thermally stimulated luminescence (TSL) process in MgAl2O4:Er3+ phosphor. Three defect centres were identified in irradiated phosphor by ESR measurements which were carried out at room temperature and these were assigned to an O− ion and F+ centres. O− ion (hole centre) appears to correlate with the low temperature TSL peak at 210 °C and one of the F+ centres (electron centre) is related to the high temperature peak at 460 °C.

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.

Thermo-stimulated luminescence of x-ray- and alpha-irradiated yttria-stabilized zirconia

Yttria-stabilized zirconia (ZrO2 : Y3+) single crystals (with 9.5 mol% Y2O3) were irradiated with x-rays and α particles. Thermally stimulated luminescence (TSL) data show a main broad peak centred at ∼500–550 K in the glow curves of all irradiated samples. The TSL peak maximum temperature is consistent with the characteristic recovery temperature (∼450 K) of colour centres (T centres) deduced from isochronal annealing curves measured by electron paramagnetic resonance (EPR) spectroscopy. However, the trap-depth energies (ranging between 0.8 and 1.2 eV) deduced from the initial rise of partially cleaned TSL peaks (and from a rough approximation using Urbach’s formula) are much larger than the activation energies for defect recovery of 0.3 eV deduced from the EPR data. A second TSL peak centred at ∼350–450 K found in freshly irradiated samples is seen to decay substantially in aged samples. The processes involved in TSL are discussed in relation to the defect annealing processes, and available defect-level energy and TSL data.

Luminescence and recombination processes in bulky Li6Gd x Y1 − x (BO3)3:Eu crystals

The luminescence and recombination processes in crystals of lithium borates Li6GdxY1 − x(BO3)3:Eu have been investigated. The steady-state X-ray luminescence (XRL) spectra, the temperature dependences of the XRL intensity, and the thermally stimulated luminescence (TSL) spectra have been measured for the Li6Gd(BO3)3, Li6Eu(BO3)3, Li6Y0.5Gd0.5(BO3)3:Eu, and Li6Gd(BO3)3:Eu compounds in the temperature range of 90–500 K. It is established that the band at 312 nm, which is due to the 6PJ → 8S7/2 transitions in Gd3+ ions and the group of lines at 580–700 nm, which are due to the 5D0 → 7FJ (J = 0 … 4) transitions in Eu3+ ions dominate in the XRL spectra. The XRL intensity in these bands increases several times with a change in temperature from 100 to 400 K for undoped crystals. The likely mechanisms of the observed temperature dependence of the XRL intensity and their relationship with the features of electronic-excitation energy transfer in these crystals are discussed. The spectra of all crystals under study exhibit a dominant composite TSL peak with a maximum at 110–160 K and a series of weaker peaks, the composition and structure of which depend on the crystal type. The nature of the shallow traps, which are responsible for the TSL at temperatures below room, and their relationship with the defects of lithium cation sublattice are discussed.

ZnGa_2O_4:Cr^3+: a new red long-lasting phosphor with high brightness

ZnGa2O4:Cr3+ is shown to be a new bright red UV excited long-lasting phosphor potentially suitable for in vivo imaging due to its 650 nm-750 nm emission range. Photoluminescence and X-ray excited radioluminescence show the 2E → 4A2 emission lines of both ideal Cr3+ and Cr3+ distorted by a neighboring antisite defect while long-lasting phosphorescence (LLP) and thermally stimulated luminescence (TSL) almost exclusively occur via distorted Cr3+. The most intense LLP is obtained with a nominal Zn deficiency and is related to a TSL peak at 335K. A mechanism for LLP and TSL is proposed, whereby the antisite defect responsible for the distortion at Cr3+ acts as a deep trap.

Thermally stimulated luminescence in aluminium nitride crystals

AbstractElectronic levels of point defects in aluminium nitride (AlN) bulk single crystals are evaluated using thermally stimulated luminescence (TSL). As the crystals were grown using AlN source material of different purity levels, the samples show different concentrations of silicon, oxygen, carbon, and (presumably) vacancies and vacancy complexes. In the TSL spectra, broad peaks are detected around 40–70 K, 100 K, 170 K, 220 K, 260 K, and 390 K. The corresponding activation energies were calculated using the Hoogenstraaten method to 8–35 meV, 40–70 meV, 150–215 meV, 130–180 meV, 150–190 meV, 80–170 meV, and 590–770 meV, respectively. TSL peak intensities are discussed in terms of chemical analysis of the samples. The results indicate that oxygen and silicon act as dominant electron traps in AlN. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Luminescence and thermally stimulated recombination processes in Li6Gd(BO3)3:Ce3+ crystals

The luminescence and thermally stimulated recombination processes in lithium borate crystals Li6Gd(BO3)3 and Li6Gd(BO3)3:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the 6 P J → 8 S 7/2 transitions in Gd3+ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at 400–420 nm, which is due to the d → f transitions in Ce3+ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100 to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160 K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation with defects in the lithium cation sublattice are discussed.

Characterization, photoluminescence, thermally stimulated luminescence and electron spin resonance studies of Eu 3+ doped LaAlO 3 phosphor

Europium-doped lanthanum aluminate (LaAlO 3) powder was prepared by using a combustion method. The crystallization, surface morphology, specific surface area and luminescence properties of the samples have been investigated. Photoluminescence studies of Eu doped LaAlO 3 showed orange-reddish emission due to Eu 3+ ions. LaAlO 3:Eu 3+ exhibits one thermally stimulated luminescence (TSL) peak around 400 °C. Room temperature electron spin resonance spectrum of irradiated phosphor appears to be a superposition of two centres. One of them (centre I) with principal g-value 2.017 is identified as an O − centre while centre II with an isotropic g-value 2.011 is assigned to an F + centre (singly ionized oxygen vacancy). An additional defect centre observed during thermal annealing around 300 °C grows with the annealing temperature. This centre (assigned to F + centre) originates from an F-centre (oxygen vacancy with two electrons) and the F-centre along with the associated F + centre appear to correlate with the observed TSL peak in LaAlO 3:Eu 3+ phosphor. The activation energy for this peak has been determined to be 1.54 eV from TSL data.

Luminescence and defect centres in Tb 3+ doped LaMgAl 11O 19 phosphors

Terbium (Tb) doped LaMgAl 11O 19 phosphors have been prepared by the combustion of corresponding metal nitrates (oxidizer) and urea (fuel) at furnace temperature as low as 500 °C. Combustion synthesized powder phosphor was characterized by X-ray diffraction and field emission scanning electron microscopy techniques. LaMgAl 11O 19 doped with trivalent terbium ions emit weakly in blue and orange light region and strongly in green light region when excited by the ultraviolet light of 261 nm. Electron Spin Resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the defect centres responsible for the thermally stimulated luminescence (TSL) process. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least two defect centres. One of the centres (centre I) with principal g-values g ∥ = 2.0417 and g ⊥ = 2.0041 is identified as O 2 − ion while centre II with an axially symmetric g-tensor with principal values g ∥= 1.9698 and g ⊥ = 1.9653 is assigned to an F + centre (singly ionized oxygen vacancy). An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F + centre) seems to originate from an F centre (oxygen vacancy with two electrons). The F centre and also the F + centre appear to correlate with the observed high temperature TSL peak in LaMgAl 11O 19:Tb phosphor.

Red persistent luminescent silicate nanoparticles

Red persistent luminescent diopside nanoparticles doped with Mn 2+ and codoped with RE 3+ (Eu 2+ , Dy 3+ ) have been obtained by sol-gel method. The influence of codoping rare earth ions on the persistent luminescence was studied by wavelength-resolved thermally stimulated luminescence (TSL) measurements from 30 to 650 K after X-ray irradiation. From these first results, a mechanism of persistent luminescence is proposed. In this mechanism Mn 2+ and Eu 2+ act as TSL recombination centers, Mn 3+ and Eu 3+ being stable hole centers, whereas Dy 3+ acts as a good electron trap giving rise to a TSL peak at high temperature. Finally, persistent luminescence was measured. Intensity and persistence of the red luminescence of CaMgSi 2 O 6 : Mn 2+ -Dy 3+ are better than those of CaMgSi 2 O 6 : Mn 2+ and CaMgSi 2 O 6 : Mn 2+ -Eu 2+ , which are in agreement with the results of TSL.

Intrinsic trapping and recombination centers inCdWO4investigated using thermally stimulated luminescence

An investigation of carrier trapping and recombination processes in ${\text{CdWO}}_{4}$ crystals undoped and Li doped has been performed by wavelength-resolved thermally stimulated luminescence (TSL) studies following x-ray irradiation at 10 K. Particular focus has been paid to the temperature region from 10 to 100 K where as many as five TSL peaks were detected, with trap depths from 0.07 up to 0.19 eV. Two of them (at 61 and at 75 K) could be ascribed to the thermal detrapping of self-trapped holes (STH) and their subsequent radiative recombination with electrons localized at intrinsic defect sites. This ascription derives from the strong similarity of their energies and frequency factors ($E=0.07\text{ }\text{eV}$ and $s={10}^{4}\text{ }{\text{s}}^{\ensuremath{-}1}$, $E=0.08\text{ }\text{eV}$ and $s={10}^{4}\text{ }{\text{s}}^{\ensuremath{-}1}$) with those of recently studied STH paramagnetic defects. The TSL emission spectrum features both the intrinsic emission at 2.5 eV probably originating from the ${({\text{WO}}_{6})}^{6\ensuremath{-}}$ group and a further band at 1.9 eV previously ascribed to a transition within a ${({\text{WO}}_{6})}^{6\ensuremath{-}}$ group lacking of an oxygen ion. Our findings allow a detailed discussion on the trapping-recombination processes in ${\text{CdWO}}_{4}$, also in comparison with those occurring in another tungstate like ${\text{PbWO}}_{4}$. Moreover, the possible role of the detected traps in the scintillation performance of the crystal is discussed.

Thermoluminescence and absorption spectra of CdSe quantum dot-doped glass irradiated by X-rays

Thermally stimulated luminescence (TSL) of aluminoborosilicate glass doped with CdSe nanoparticles (28 and 47 Å) has been studied after exposure to ionizing radiation; the intense TSL peaks were observed at temperatures 150 and 85 °C, respectively. The optical absorption spectra, as well as TSL of the irradiated samples containing CuBr nanoparticles (44 Å) were also measured. In the case of CuBr, TSL was observed neither before nor after irradiation. The dependence of TSL intensity on irradiation time indicates that glass activated by CdSe nanoparticles shows promise as a dosimetric material.