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The use of aliovalent sintering aids, especially TEOS, for scintillation ceramics preparation caused serious problems due to the need for charge compensation. Isovalent ions, on the other hand, do not cause such a problem and remain a new field to be explored. By using La 2 O 3 and Sc 2 O 3 isovalent sintering aids, we succeeded to produce Pr:LuAG ceramics with pure LuAG phase, good micro-structure, and characterized by high optical quality with 80% transmittance in the visible range. Luminescence and scintillation properties were also investigated and turned out to be similar to those of previously studied transparent ceramics obtained with aliovalent sintering agents. Thermoluminescence data show the presence of several trapping states experiencing a disordered surrounding. It can be concluded that sintering aids, regardless of their valence, introduce local disorder due to their different radii with respect to that of the lattice ions resulting in the appearance of a UV emission and decrease of Pr 3+ fast 5d–4f luminescence intensity. The aspects of energy transfer and trapping due to sintering aids in LuAG lattices are discussed.

We employ a combination of first-principles calculations and optical characterization experiments to explain the mechanism by which Ga3+ doping prevents the trapping of free carriers due to shallow traps in RE 3Al5O12 garnet scintillators (where RE represents a 3+ rare-earth cation). Specifically, we confirm that Ga3 + doping does not reduce the defect concentration (defect engineering), but rather leads to shifts in the valence and conduction bands such that the energy level of shallow defects is no longer in the forbidden gap where electrons can be trapped (band-gap engineering).

About 20 μm thick Ce-doped Lu 3 Al 5 O 12 thin films grown by Liquid Phase Epitaxy and thin plates of similar thickness prepared by mechanical cutting and polishing from Czochralski grown crystals are used in 2D-imaging experiment down to μm 2D-resolution. Their scintillation response is also measured under α-particle excitation and performance of film and bulk material is mutually compared. Furthermore, scintillation and thermoluminescence characteristics of UV emitting Sc-doped LuAG grown by Czochralski method are presented since this system is a candidate material for UV emission-based 2D sensors with improved diffraction limit with respect to the presently used Ce-doped aluminum garnets.

Four types of electron traps in PbWO4, based on regular W sites perturbed by oxygen vacancies, are identified by electron spin resonance (ESR). The analysis of the ESR spectra parameters (g-factor values and principal-axes orientations) shows that the revealed centers are (WO3)(-) vacancy-containing complex anions associated with a defect in the Pb sublattice: (WO3)(-)-A(Pb) complexes. Two of the centers (W-1 and W-2) are thermally stable up to 350-370 K, while the other two (W-3 and W-4) are stable only up to 270-290 K. Above these temperatures the trapped electrons become free and recombine with localized holes, giving rise to a composite TSL glow peak at Tapproximate to323 K (characterized by a trap depth of 0.9 eV evaluated by the initial rise method) and to a weaker TSL structure at Tapproximate to365 K. The correspondence between (WO3)(-)-A(Pb) centers and TSL peaks is supported by their similar room temperature time decays, and by the similar dependences of ESR and TSL signals upon annealing treatments. A scheme of local electronic levels in the band gap of PbWO4 is proposed.

Ce,Mg:LuAG scintillation ceramics with Ce dopant content ranging from 0.025 at.% to 0.3 at.% and constant 0.2 at.% Mg codoping were fabricated by solid-state reaction. The effects of Ce concentration and annealing conditions on the microstructure, optical quality and scintillation properties are studied in great details. Lattice parameters as well as the absorption, photoluminescence, radioluminescence and thermoluminescence characteristics are investigated as a function of Ce content. Both the photoluminescence and scintillation decays are measured as well in order to study re-absorption and concentration quenching processes. In addition, an enhanced positive effect of air annealing on radioluminescence intensity and light yield is put in evidence. Moreover, the role of the charge transfer absorption of Ce^(4+) is investigated. Thermoluminescence measurements are performed to investigate the influence of both air annealing and Ce concentration on defects acting as traps. Finally, the correlations among steady state scintillation efficiency, light yield, thermoluminescence and Ce^(3+) concentration are found and discussed.

Six Mg2+ co-doped Lu3Al5O12:Ce scintillating garnet films prepared by liquid phase epitaxy, with Mg concentration from 0 to 3000 ppm, were irradiated by X-rays and underwent a series of thermoluminescence measurements from 10 to 720 K. The thermoluminescence signal of epitaxial films originated purely from electron recombination at Ce ions. It was found that the area of all the peaks present in thermoluminescence glow curves decreased rapidly with the increase of Mg concentration; for 3000 ppm, the decrease was by 4–5 orders of magnitude. Moreover, the bright burn effect was significantly suppressed by Mg co-doping. Possible explanations, i.e., trap concentration reduction or increased competition in free electron capture between thermoluminescence traps and Ce4+ centers, were discussed.

The process of hole and electron localization in LuAG:Ce,Mg ceramics is studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL). Hole traps, which are created by UV irradiation, are detected in the form of O− centers. Mg-perturbed variants of O− centers are proposed to exist. The thermal stability of such defects is studied, proving that they are stable up to room temperature. The interaction between O− centers and shallow electron traps is studied by thermally stimulated luminescence (TSL) and phosphorescence experiments, which reveal the occurrence of an a-thermal tunneling process between trapped electrons and randomly distributed Ce centers. By correlating the TSL-derived trap parameters and temperature dependent ESR intensities, it is found that O− centers compete with Ce centers in free electron capture.

A numerous set of Pr-doped YAP single crystals was prepared using Czochralski and micro-pulling down methods. Crystals codoped by bi-, tri- and tetravalent ions were prepared by the latter method as well. The scintillation performance of all the prepared materials was evaluated using radioluminescence, photoelectron yield and scintillation decay measurements at room temperature. The influence of shallow traps was studied by means of thermoluminescence in the 10-350 K temperature range. Though the intrinsic scintillation efficiency of Pr-doped YAP is higher than that of YAP:Ce, enhanced delayed radiative recombination processes are found to be responsible for lower-than-expected photoelectron yield of the former system. The possibilities of further optimization of Pr-doped YAP scintillator are discussed. © 2010 IEEE.

This paper deals with some aspects of scintillation response of Ce-doped Y-Lu aluminum garnets or perovskites in comparison with Ce-doped orthosilicates. An essential difference between the Ce-doped aluminum garnets/perovskites and orthosilicates consists in larger fluctuations of photoelectron yield of the latter scintillators where differences can reach up to 50% and measured values critically depend on the recent history of the sample (illumination by day light, thermal annealing, etc.). This behavior of Ce-doped silicates seems to be due to the vicinity of the 5d1 level of Ce3+ from the conduction band, which makes the material more sensitive to the presence of deep electron traps monitored by thermo-luminescence above room temperature. The presence of such electron trapping sites thus appears more critical than in aluminum garnets/perovskites.

Effect of Ga substitution in the (Lu, Pr) 3Al 5O 12(Pr : LuAG) scintillator was examined at the crystals grown by the micropulling down (μ-PD) method. Host luminescence due to an exciten localized around the Lu-Al antisite defect was suppressed by Ga admixture. Concentration depenendence was investigated and suppression was observed even at the lowest Ga concentration of 5 mol%. Faster decay time as well as less intense slower components were obtained upon increasing the amount of Ga. In the thermostimulated luminescence measurement, the glow curve peaks are gradually shifted to lower temperatures with the gallium admixture, and noticeable intensity decrease was observed only for the (Lu, Pr) 3(Ga 0.2Al 0.8) 5O 12. The undesired quenching effect of Ga on the Pr 3+ luminescence seems to be reasonably low up to (Lu, Pr) 3(Ga 0.2Al 0.8) 5O 12 sample. It is estimated to introduce nonradiative losses of less than 10% with respect to Ga-free Pr:LuAG. Bulk crystals were also grown by the Czochralski (Cz) method and these effects were confirmed. © 2008 IEEE.

This paper deals with Pr-doped and Pr, Si-codoped YAlO3 single crystal growth by the micro-pulling-down method and investigation of their spectroscopic and scintillating properties. The Pr3+ 5d -4f radioluminescence intensity is more than 10 times higher than that of Bi4Ge3O12 standard sample, but the Si-codoping decreases it. Absorption spectra of as-grown and air-annealed Si,Pr-codoped YAlO3 samples show along with an onset of 4f -5d transition round 230 nm the induced absorption band at 400 nm which possibly related to a hole center absorption (Pr4+ or O-). Thermoluminescence measurements above the room temperature were performed in order to monitor deep electron traps. Strong concentration dependence of thermoluminescence was observed for Pr:YAlO3 glow curves. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Single crystals of PbWO 4 and Lu 3 Al 5 O 12 -based scintillators were studied by correlated electron paramagnetic resonance and thermally stimulated luminescence experiments. The nature of some of the intrinsic trapping centers and their role in the energy transfer and storage processes were explained. Examples of material doping and co-doping are given, which succeeded in suppression of specific point defects and improvement of scintillation performance.

Doped Bi4Ge3O12 (BGO) fiber single crystals were grown by the micro-pulling-down method with the resistance heating system. Optical absorption measurements before and after x-ray irradiation (induced absorption) were performed in order to investigate the radiation damage of the crystals. The Eu3+doped BGO has shown higher radiation resistance with respect to the equivalently grown undoped BGO fibers. Radio- and photoluminescence characteristics were obtained to clarify the role of Eu3 in luminescence and scintillation mechanism. Radioluminescence spectra show the intense and slow (decay time of 1.61 ms) D-5(0,1)-F-7(x)(x=0-6) radiative transitions of Eu3, while the intrinsic BGO emission becomes weaker with respect to the undoped BGO. Photoluminescence decay of the intrinsic BGO emission becomes nonexponential and noticeably faster in Eu-doped samples, which evidences the nonradiative energy transfer from intrinsic emission centers to Eu3 ions. Thermally stimulated luminescence (TSL) measurements above room temperature prove that Eu3 doping strongly influences the concentration of TSL active traps. (C) 2003 American Institute of Physics.

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 Pb 2+) 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. © 2009 Elsevier Ltd. All rights reserved.

LiCaAlF6 (LiCAF) crystals doped with two different rare earth (RE) ions (europium and cerium) have been investigated as potential new dosimetric materials. Thermally stimulated luminescence (TSL) measurements have been carried out and a quantitative comparison has been performed with a standard LiF dosimetric material. Wavelength-resolved TSL measurements have revealed that the TSL spectrum is dominated by RE-related emissions with no significant contributions from defect centers. The glow curve of LiCAF:Eu displays a dosimetric peak at about 240 degrees C with a good linearity versus imparted dose. Specifically, the material appears more sensitive than LiF at doses lower than 100 mGy (with a sensitivity limit of 10(-5) Gy). Concerning LiCAF:Ce, the glow curve is more complicated, dose memory effects appear and no peaks with good dosimetric properties are found. Therefore, LiCAF:Eu seems to be more promising in the search for a new dosimetric material. (c) 2006 Elsevier B.V. All rights reserved.

The cover picture of the current issue refers to the Rapid Research Letter by Martin Nikl et al. [1]. It depicts the structure of a Lu3Al5O12:Ce single crystal, a possible high performance scintillator material. Its scintillation performance is, however, degraded by the occurrence of antisite defects. Such defects arise in the material structure sketched in the figure due to the occurrence of Lu3+ ions at the Al3+ octahedral sites as seen in the middle left octahedron. This defect constitutes a shallow electron trap, which delays energy delivery to the Ce3+ emission centers, and thus slows down the scintillation response of the material. Thermoluminescence measurements appear as sensitive diagnostic tool to evidence these defects in the single crystals grown. Martin Nikl is senior scientist and head of the Laboratory of Luminescence and Scintillation Materials at the Institute of Physics of the Czech Academy of Sciences. His main research activities include the characterization of the luminescence and scintillation properties of wide band-gap materials and the influence of material defects on them.

Scintillation, radioluminescence, photoluminescence, and thermoluminescence characteristics of Czochralski-grown YbxY1-xAlO3 single crystals for x=0.02-0.45 are described. Under x-ray excitation, the intensity of Yb3+ charge-transfer luminescence is increasing with x and reaches at room temperature more than 11% of Bi4Ge3O12 (BGO) for x=0.45, while at 80 K it is over 170% of BGO for xgreater than or equal to0.3. At room temperature, scintillation decay shows a dominant decay time of 0.8-0.9 ns for xgreater than or equal to0.3 and no significant slow components were detected. The photoluminescence decay time is tuned by temperature and Yb concentration from tens of nanoseconds at 80 K down to about 0.8 ns at 295 K. Thermoluminescence glow curve below room temperature evidences very low concentration of shallow traps compared to the Ce-doped YAlO3 scintillator. (C) 2004 American Institute of Physics.

We study trapping states of Ce 3+ -doped SrHfO 3 by thermally stimulated luminescence in a wide temperature range (10–730 K). We determine characteristic parameters of the traps by the initial rise technique. We also determine the energy of thermal ionization of the excited state of Ce 3+ in SrHfO 3 host by purely optical method based on the study of UV illumination-induced thermoluminescence. The method provides a value of the thermal ionization energy of about 0.25 eV.

We improve a recently proposed approach for the evaluation of the thermal ionization barrier of the lanthanide excited states in luminescent materials by taking into account the effect of traps and their decay time temperature dependence. We present two distinct methods, and we apply them to the case of Lu${}_{2}$Si${}_{2}$O${}_{7}$:Pr. To this purpose, wavelength resolved thermally stimulated luminescence and photoluminescence time decay measurements extending up to the ms time scale have been performed. In the frame of the first method, the thermal ionization barrier of the Pr${}^{3+}$ $5{d}_{1}$ excited state has been evaluated by studying the progressive filling of traps during illumination by ultraviolet light within the 4$f$-5${d}_{1}$ absorption band of Pr${}^{3+}$ at different temperatures. The thermal ionization barrier turned out to be 0.54 $\ifmmode\pm\else\textpm\fi{}$ 0.05 eV. In the second approach this parameter has been calculated by a numerical reconstruction of the temperature dependence of the 5${d}_{1}$-4$f$ delayed recombination decay integral in two different time windows ([53.3 $\ensuremath{\mu}$s $\ensuremath{-}$ 10.3 ms] and [53.3 $\ensuremath{\mu}$s $\ensuremath{-}$ 600 s]) with the sum of contributions from different traps whose parameters have been investigated by thermally stimulated luminescence (TSL). The results obtained are in agreement with those found using the trap-filling method. The advantages and limits of both approaches have been critically exposed, in order to discuss the possibility of their extensive employment for the determination of the ionization barrier of a rare earth ion excited-state level in an insulating host.

We study defect states in Pr3+-doped Lu2Si2O7 crystal by wavelength resolved thermally stimulated luminescence both below and above room temperature. We identify the TSL peaks, analyze them by the initial rise technique and calculate the characteristic parameters of the corresponding traps. The role of tunnelling of charge carriers between traps and recombination centers up to RT is observed and discussed. The TSL spectra show that the charge carrier recombination predominantly occurs at Pr3+ centers. We also provide some comparison with the LPS:Ce3+ crystal prepared by the same method. (C) 2011 Elsevier B.V. All rights reserved.

We study defect states in undoped and Eu3+-doped Lu 3GaxAl5-xO12 (x = 0-5) garnet crystals by wavelength resolved thermally stimulated luminescence above room temperature. Eu3+ ions act not only as recombination centres but also as high temperature traps, as testified by the presence of a TSL peak at 450 °C correlated with Eu3+-doping. With increasing gallium content all glow peaks are shifted to lower temperatures. This trend is confirmed also for powder samples prepared by sol-gel technique. The observed low temperature shift of the glow peaks can be considered as a consequence of the band gap reduction following the increase of Ga3+ concentration. The comparison with the glow curve of a Ce3+-doped crystal is also shown. © 2010 Elsevier B.V. All rights reserved.

We bring into consideration a novel, potentially promising scintillating material, Pb-doped SrHfO3. The structural and optical properties of a series of Pb-doped SrHfO3 powders prepared by acetate and citrate combustion are investigated and compared to those of undoped and Ce-doped powders with the same composition. Room temperature radioluminescence studies as a function of sintering temperature show that samples sintered up to the highest final temperature (1150 degrees C) display the highest light output. Moreover, Pb-doped SrHfO shows a higher radioluminescence efficiency with respect to Ce-doped SrHfO3, which in turn features a very fast photoluminescence decay time of 15 ns. The presence of point defects and their role in carrier trapping are studied by thermally stimulated luminescence as well as by radioluminescence as a function of temperature.

Photo- and radioluminescence, decay kinetics, and thermoluminescence are reported for a set of Ce3+-doped phosphate glasses. The presence of Gd3+ ions in the glass host matrix at concentrations above 20% enhances the energy transfer towards the Ce3+ emission centers, which results in a remarkable enhancement of the radioluminescence light output. (C) 2000 American Institute of Physics. [S0003-6951(00)04340-0].

This note provides a direct comparison between YAP:Ce{sup 3+} and LuAG:Ce{sup 3+} scintillators grown in the same laboratory as for radioluminescence light output, scintillation decay and thermoluminescence characteristics. A correlation between the occurence of thermo-luminescence (TSL) peaks round RT and of very slow components in the scintillation decay of LuAG:Ce{sup 3+} is revealed. Importance of understanding of the nature of such TSL active trapping states and their removal for further optimisation of LuAG:Ce{sup 3+} scintillator is concluded. (orig.)

We investigate and compare optical absorption, luminescence and scintillation properties of Pr-doped Y3Al5O12, Lu3Al5O12, Y2SiO5 and Lu2SiO5 single crystals. The processes determining the kinetics of the fast Pr3+ 5d–4f radiative transition are described. Among the studied host materials, only Lu3Al5O12 presents neither any 5d1–4f luminescence state nonradiative quenching nor Pr3+ ionization at room temperature. We evaluate the figure of merit of all materials for application as scintillators. The most promising system appears to be Lu3Al5O12 : Pr, since it combines an elevated density of 6.67 g cm−3, a fast scintillation response dominated by a 21 ns decay time and a spectrally corrected light yield about 160% with respect to that of Bi4Ge3O12 (BGO).

We present an investigation of defects acting as electron traps in ${\text{Lu}}_{2}{\text{SiO}}_{5}$ (LSO) and ${\text{Lu}}_{x}{\text{Y}}_{2\ensuremath{-}x}{\text{SiO}}_{5}$ (LYSO) performed by wavelength-resolved thermally stimulated luminescence (TSL) measurements from 20 to $400\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ after room-temperature (RT) x-ray irradiation. Single crystals doped with several rare-earth ions such as Ce, Tb, Tm, and Sm were considered. A comparison between TSL and RT radio-luminescence (RL) emission spectra is also presented. The glow curves for both LSO and LYSO are similar, showing a series of TSL peaks at 78, 135, 181, and $236\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. In addition, a further peak at about $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ is observed only in LYSO. Our results confirm the role of oxygen vacancies as electron traps in the material; the presence of several glow peaks with a unique trap depth $(0.99\text{ }\text{eV}\ifmmode\pm\else\textpm\fi{}0.07\text{ }\text{eV})$ for the 78, 135, 181, and $236\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ peaks is explained by suggesting that electrons stored in oxygen vacancies recombine through a thermally assisted tunneling mechanism with holes localized at ${\text{Ce}}^{3+}$ or ${\text{Tb}}^{3+}$ centers residing on Lu sites at different crystallographic distances from the traps. This model is supported by the very good correlation among O-Lu distances in the monoclinic $C2/c$ structure of LSO and LYSO and the frequency factors of the traps containing the transmission coefficients of the potential barriers between traps and centers, evaluated in the framework of the thermally assisted tunneling process. Tm and Sm ions do not act as TSL recombination centers possibly due to their tendency to trap electrons during irradiation with ionizing radiation.

Zr,Pr-codoped and Si,Pr-codoped YAlO3 single crystals were grown from the melt by the micro-pulling-down method. The effect of Zr/Si-codoping on YAlO3:Pr scintillation properties, such as radioluminescence, scintillation light yield and decay time, was investigated. Absorption spectra of as-grown and air-annealed samples reveal the presence of color centers. The possible nature of the charge traps detected by high temperature thermoluminescence is discussed.