EPR,thermoluminescence, and thermally stimulated conductivity in BaWO4 crystals

In BaWO₄ crystals electrons and holes trapped at WO₄ complexes are identified by electron paramagnetic resonance (EPR) after X-irradiation at T = 80 K. The thermal decay of the intrinsic hole centres at about 100 K is accompanied by a simultaneous decrease of electron traps (WO₄)^3- and glow maxima of thermoluminescence (TL) and of thermally stimulated conductivity (TSC). This connection is explained by a thermally activated hopping of the $\text{(WO}{}_4\text{)}\text{3-}\text{2}$ hole centres followed by radiative recombination with electron traps (WO₄)^3-. A qualitative kinetic calculation based upon EPR data and the shift between TL and TSC glow peak confirms this model.     

Electric field effect on the mechanisms of recombination in KI doped with divalent ions

In KI crystals doped with divalent ions (Eu²⁺, Sr²⁺, Mn²⁺) a strong influence of the electric field is observed, after irradiation, on the carriers (electrons and holes) recombination kinetics. The phenomena are similar whether the electrons, distributed on traps bound to divalent ions, are excited by IR at 4 K, and recombine with trapped holes (V_k centers) or whether the holes are made thermally mobile at T>77 K. It is suggested that this is due to the recombination mechanism: the kinetics are simultaneously controlled by diffusion and tunneling. The tunneling range is a function of the applied field.     

Effect of 100 MeV swift Si8+ ions on structural and thermoluminescence properties of Y2O3:Dy3+nanophosphor

Nanoparticles of Y₂O₃:Dy³⁺ were prepared by the solution combustion method. The X-ray diffraction pattern of the 900°C annealed sample shows a cubic structure and the average crystallite size was found to be 31.49?nm. The field emission scanning electron microscopy image of the 900°C annealed sample shows well-separated spherical shape particles and the average particle size is found to be in a range 40?nm. Pellets of Y₂O₃:Dy³⁺ were irradiated with 100?MeV swift Si⁸⁺ ions for the fluence range of 3?×?10^11_3?×?10¹³ ions cm^?2. Pristine Y₂O₃:Dy³⁺ shows seven Raman modes with peaks at 129, 160, 330, 376, 434, 467 and 590?cm^?1. The intensity of these modes decreases with an increase in ion fluence. A well-resolved thermoluminescence glow with peaks at ～414?K (T_m1) and ～614?K (T_m2) were observed in Si⁸⁺ ion-irradiated samples. It is found that glow peak intensity at 414?K increases with an increase in the dopant concentration up to 0.6?mol% and then decreases with an increase in dopant concentration. The high-temperature glow peak (614?K) intensity linearly increases with an increase in ion fluence. The broad TL glow curves were deconvoluted using the glow curve deconvoluted method and kinetic parameters were calculated using the general order kinetic equation.     

Influence of nitrogen implantation on thermoluminescence of synthetic quartz

Thermoluminescence (TL) of synthetic quartz exposed to beta irradiation following implantation with 60?keV N⁺ ions at fluences ranging between 1?×?10¹⁴ and 5?×?10¹⁵?ions/cm² is reported. The glow curve measured at 5°C/s typically consists of a prominent peak near 110°C, studied in this work, and minor glow peaks at around 130°C and 190°C. The TL intensity of the main peak increased both with implantation and with fluence of implantation. The dependence of the intensity on heating rate and fluence suggests that the implantation introduces new defects that may possibly act as recombination centres. The increase in TL intensity with the heating rate exhibited by implanted samples has been observed in other luminescence materials. This anti-quenching phenomenon has been described as a competition effect between multiple luminescence pathways in luminescence materials. Kinetic analysis of the main glow peak using the initial rise, various heating rate and glow curve deconvolution methods shows that the activation energy of the main peak is about 0.7?eV with no systematic change due to ion fluence.     

Über Zusammenhänge zwischen Elektronenspinresonanz,elektrischer Leitfähigkeit und Photoleitung bei reinem und dotiertem Bor

The conductivity mechanism in pure and doped, β-rhombohedral, polycrystalline boron between 1.5 °K and 900 °K is clarified by measurements of electrical conductivity, photoconductivity, electron paramagnetic resonance and thermoelectric effect. The semiconductor behaviour of boron between 1.5 and 900 °K is similar to that of doped and compensated germanium and silicon at helium temperatures concerning the temperature-independent number of carriers and the thermally activated conduction process at low and high carrier concentrations. The paramagnetic centres are nearly localized electrons at 1.5 °K and nearly free electrons at 900 °K with a continuous transition between these two extreme kinds of behaviour. Mobilities of charge carriers in carbon doped boron over a range from 10¹⁶ cm^?3 to 10²⁰ cm^?3 and 77 °K to 900 °K were measured for the first time and were found to obey an exponential law.     

Photostimulated thermoluminescence of x-irradiated NaCl

The thermoluminescence and photostimulated thermoluminescence of X-ray coloured NaCl crystals has been studied, together with the thermal annealing of F, F′ and M centres. Three glow peaks centred at 315, 341 and 348°K are obtained in the temperature range 300–400°K. The first peak (315°K) is ascribed to electron trapping by Cu²⁺ centres formed by X-irradiation. The other peaks (314 and 348°K) are related to the thermal annealing of M and F centres, respectively.     

Messungen von Anregungstemperaturen in der Hochstromhohlkathode

Measurements of excitation temperatures in the negative glow light of a high-current hollow cathode discharge lamp with a gas temperature of about 1,500 °K have shown values forT _a of approximately 5,000 °K, when the atomic spectral lines are used as indicator. However, from ionic lines a temperature of 30,000–100,000 °K is deduced depending on the nature of the discharge gas. This big difference indicates that there is no Maxwell distribution in the hollow cathode discharge. A possible explanation could be that two energetically distinct types of electrons take part in ionisation and recombination respectively.     

Das Emissionsspektrum gebundener Excitonen in Zinkoxydkristallen in Abhängigkeit von Temperatur und uniaxialer Verspannung

The recombination radiation of bound excitons in ZnO-crystals (spectral range 3,38–3,35 eV at 4.2 °K) and the adjacent phonon-assisted spectrum have been studied at temperatures between 4.2 °K and 90 °K. The phonon-assisted spectrum changes its structure at about 30 °K. With increasing temperature the exciton lines shift toward smaller quantum energies (ΔE～T ²) and their half widthH increases (H～T ²). The line shift is explained by a band gap variation due to deformation potential coupling of the holes toTA phonons. The line width is explained by broadening of an infinitely sharp line under the influence of the mean square fluctuation of thermally generated crystal deformations. The influence of uniaxial stress on the spectral positions of the lines has been studied.     

Thermolumineszenz von KCl und NaCl nach Röntgen- und UV-Bestrahlung bei Heliumtemperatur

Glow curves of luminescence are recorded in the range from 10° K to 300° K. One gets characteristic changes by prior annealing the single crystals in O₂ or HCl. Also an increase of the lattice disorder causes new glow bands. In KCl a strong glow band always appears at 40° K after irradiating with X-rays or ultraviolet light in the range of the exciton bands. It is ascribed to trapped excitons, which become mobile at that temperature. For X-ray irradiated KCl the glow curve of luminescence is compared with the electrical glow bands and with the concentration change of known defects. The half widthΔT of all glow bands is found proportional to the temperature of the maximum:ΔT=(0.08±0.02)T _m .     

Stimulated self-trapped exciton emission in CsI:Pb

Defects of the type of V_K and Pb⁺ centres were created in CsI:Pb under the 4.03 eV XeCl laser line irradiation at 10 K. After irradiation, the self-trapped and localized exciton emission excited by the same XeCl laser line was observed as a result of the recombination of electrons, optically released from Pb⁺, with the V_K centres. A strongly superlinear dependence of the emission intensity on the excitation intensity was found for the 3.65 eV emission of the self-trapped exciton. A much weaker superlinearity was observed for the visible localized exciton emission. Optical amplification of the exciton emission was considered as the most probable reason of the observed phenomenon. At 10 K, optical gain G=3.74 was calculated for the self-trapped exciton emission.     

Kinetic analysis of high temperature secondary thermoluminescence glow peaks in α-Al2O3:C

The kinetic analysis of secondary glow peaks in carbon-doped aluminium oxide is reported. A glow curve measured at 0.4 °C s⁻¹ after beta irradiation to 3 Gy revealed at least five peaks as a result of various techniques of glow curve resolution; the dominant peak at 156 °C (peak II) and two weaker-intensity secondary peaks one at 36 °C (peak I) and the other at 264 °C (peak III). Peaks IIA and IV at 170 and 422 °C respectively only became apparent after removal of preceding more prominent peaks. The secondary peaks are particularly weak in intensity and are as usual dominated by the main dosimetry peak. The analysis in this report focusses on peak III, usually seen adjacent to the main dosimetry peak but whose presence is masked by the extreme sensitivity of the latter. Complementary analyses of the weaker intensity peaks I, IIA and IV are included. Peaks I, IIA and III are subject to first-order kinetics while for peaks II and IV the issue is less conclusive. The activation energy increases from 0.72 eV for peak I to about 1.3 eV for peak IV with values for peak II and IIA similar at ∼1 eV. In general, the frequency factor corresponding to the lower temperature peaks (I, II, and IIA) have values (10¹⁰–10¹² s⁻¹) that are an order of magnitude or so greater than for peaks III and IV (10⁹–10¹¹ s⁻¹). Except for peak I, peak II and all other secondary peaks are affected by thermal quenching whose activation energy was determined as ΔE = 0.95 ± 0.04 eV using peak IIA and as ΔE = 1.48 ± 0.10 eV using peak III. The overall conclusion is that all peaks correspond to electron traps and are associated with the same recombination centre.     

Radiation induced defects in KBr:Tl+ crystals

The defects produced in KBr:Tl⁺ crystals during x-irradiation at 77 K were studied using thermoluminescence (TL), thermally stimulated currents (TSC), and absorption and emission spectra. Three main glow peaks at 165, 193 and 258 K were observed both in the TL and in the TSC curves. A variety of irradiation induced absorption bands were observed in the UV, visible and infrared up to about 2 microns. The 165 K TL peak was found to emit only the 440 nm band assigned to thallium dimers, while the peaks at 193 and 258 K exhibited the UV bands at 310 and 365 nm as well as the 440 nm band.The defects produced during the irradiation were the V_k hole center, the Tl° and the Tl⁺₂ electron centers. Smaller concentrations of Tl²⁺ and (Tl⁺)⁺₂ centers were also produced.An analysis of the results including measurements on lightly and heavily doped crystals enabled to draw conclusions on the nature of the defects and on the recombination processes involved. A close correlation has been found between the temperatures at which changes in the various absorption bands take place and the temperatures of the TL peaks. The analysis enabled also a full classification of the absorption bands.     

EPR spectra of colour centres in x-irradiated BaCl2:K+ and BaCl2:Ag+

X-irradiation at 80°K leads to the formation of V_K centres and, in addition, perturbed F centres in the case of BaCl₂:K⁺. The V_K centres spectra exhibit a superhyperfine structure. A warming to 130°K of crystals X-irradiated at 80°K causes the V_K centres to be perturbed, and besides leads to the formation of (AgCl₄)^2? complexes in BaCl₂:Ag⁺.     

Restored thermoluminescence in oxide crystals

In this paper, we present the results of a thermoluminescence study on several oxide crystals, including Y₃Al₅O₁₂ (YAG), Y₃Al₅O₁₂:Nd (YAG:Nd), Lu₂SiO₅:Ce (LSO:Ce), Y₂SiO₅:Ce (YSO:Ce), Gd₂SiO₅:Ce (GSO:Ce), PbWO (PWO), and PbWO:La (PWO:La). A phenomenon involving restoration of thermoluminescence (TL) glow peaks is found to occur in some of the crystals investigated; crystals γ-irradiated at room temperature and subsequently stored for some time in the dark at 77 K exhibit TL glow peaks in the range below room temperature. This phenomenon is caused not by a thermally or optically stimulated process, but rather as a by-product of a tunneling process. The intensity of the restored TL glow peaks measured in LSO:Ce crystals is found to be proportional both to the radiation dose and to the storage-time at low temperature. A phenomenological theoretical model is proposed, in which tunneling recombination occurs between deep electron and hole traps accompanied by the simultaneous ejection of an electron to the conduction band; some of these conduction electrons then repopulate shallow traps. An oxygen vacancy with two trapped electrons is assumed to be the deep electron trap in this model. The role of oxygen vacancies is confirmed by heating in air at 1000 °C. This model is applied specifically to LSO:Ce, and several possible candidates are suggested for shallow traps in that material.     

Influence of argon-implantation on conventional and phototransferred thermoluminescence of synthetic quartz

Conventional and phototransferred thermoluminescence of crystalline synthetic quartz implanted with 70 keV Ar ions at fluences in the range 1?×?10¹⁴–5?×?10¹⁵?ions/cm² is reported. The glow curves, recorded at 5°C/s from beta-irradiated samples of similar mass, show a prominent peak between 100°C and 120°C. The thermoluminescence intensity of all implanted samples was greater than that of the unimplanted one. The increase in sensitivity is attributed to a corresponding increase in the concentration of point defects, as a result of the implantation, which act as electron traps or recombination centres. Kinetic analysis carried out using the peak shape, whole glow-peak and curve-fitting methods produced values of the activation energy, frequency factor and order of kinetics that are generally independent of implantation fluence. This result suggests that implantation did not necessarily affect the nature of the electron traps. With respect to phototransferred thermoluminescence, it was observed that it only appeared in the sample implanted at the highest fluence of 5?×?10¹⁵?ions/cm². This may be so because the concentration of deep traps produced as a result of implantation at low fluence is too low to give rise to phototransferred thermoluminescence. The intensity of the phototransferred thermoluminescence goes through a peak with illumination time. We attribute this behaviour to the relative concentration of holes at recombination centres and phototransferred electrons at shallow traps.     

Thermoluminescence and electron spin resonance after room-temperature X-ray irradiation of NaCl:Mn2+

A parallel investigation of thermoluminescence (TL) and electron spin resonance (ESR) spectra on room-temperature (RT) X-irradiated NaCl:Mn²⁺ has been performed. The TL spectra in the range 20–300°C consist of five glow peaks, numbered from I to V. Temperatures at maximum height are 41°, 68°, 118°, 152° and 216°C, respectively. Peaks I, II and IV obey first-order kinetics, whereas peaks III and V fit second-order behavior. The wavelength spectrum for all glow peaks consists of two bands centered at 595 and 400 nm. The 595 nm emission is attributed to hole capture by Mn⁺ and subsequent deexcitation of Mn²⁺. The 400 nm emission is produced as a consequence of hole-F center recombination.The correlation of TL glow peaks to various defects has been investigated. Peak II is clearly related to manganese-vacancy dipoles and peak I can be roughly associated to free cation vacancies. Peak IV appears to relate to large Mn-aggregates, whereas peak V is intrinsic and not related to impurities.On the other hand, ESR data indicate that each glow peak in the 595 nm emission is associated to the annihilation of a given Mn-center; Peak I to Mn⁰C, peak II to Mn⁰C and Mn⁺, peak III to Mn⁺ and peaks IV and V to Mn⁰-D.     

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 (³P_0,1–¹S₀ 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.     

Studies of intrinsic luminescence in KCl

Measurements have been made of the luminescence intensity, lifetime, emission spectra, and thermoluminescence associated with self-trapped exciton states in KCl, at temperatures of 7°K and above. These results indicate the presence of another exciton-like state in addition to the well-known state that decays by emission at 2.32 eV. Thermoluminescence glow peaks and spectra are correlated with F + V_k and F + H recombination processes.     

Synthesis,characterisation, luminescence and defect centres in solution combustion synthesised CaZrO3:Tb3+ phosphor

Tb³⁺ doped CaZrO₃ has been prepared by an easy solution combustion synthesis method. The combustion derived powder was investigated by X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy techniques. A room temperature photoluminescence study showed that the phosphors can be efficiently excited by 251 nm light with a weak emission in the blue and orange region and a strong emission in green light region. CaZrO₃:Tb³⁺ exhibits three thermoluminescence (TL) glow peaks at 126 °C, 200 °C and 480 °C. 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 centres responsible for the TL peaks. The room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0233 is identified as an O^? ion. Centre II with an axial symmetric g-tensor with principal values g_=1.9986 and g_?=2.0023 is assigned to an F⁺ centre (singly ionised 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 TL peak in CaZrO₃:Tb³⁺ phosphor.     

Further study on the influence of thermal treatments on the glow curve structure in LiF:Mg,Cu,P (GR-200A)

The influence of various annealing treatments with heating temperatures (T_A) from 240 to 700 °C, with re-annealing at 240 °C, and with a combined re-annealing procedure of 20 min at 270 °C followed by 10 min at 240 °C on LiF:Mg,Cu,P (GR-200A) was investigated. As the T_A increased, the intensity decreased rapidly to almost no signal at 340–380 °C then increased clearly and achieved a maximum at 540 °C. The position of the maximum intensity of the glow curve shifted basically in the direction of higher temperatures with an increase at T_A and achieved a maximum of 279 °C when annealed at 460 °C. The re-annealing influenced both the intensity and the glow curve structure at certain degree. The effect of re-annealing on the glow curve depended markedly on the T_A. With re-annealing at 240 °C, the intensity decreased as T_A increased up to 360 °C then increased and achieved a maximum at 540 °C. The intensity could be restored fully when annealed at above 500 °C, however, the glow curve couldn't be restored fully. With a combined annealing, the shape of glow curve of a sample annealed at above 540 °C or below 320 °C was similar to that of the standard glow curve of LiF:Mg,Cu,P and the intensity and glow curve could be restored completely when annealed in the range 620–660 °C. It seems that the main roles of the re-annealing at 240 °C are to restore partially the intensity of peak 4 and peak shape for LiF:Mg,Cu,P when annealed at above 260 °C, and restore fully the total TL intensity of LiF:Mg,Cu,P when annealed at above 500 °C and the main roles of the combined re-annealing are to reduce the intensity of peak 5 and the total TL intensity, increase the intensity of peak 4 and restore the glow curve shape.