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The influence of Mo on the electronic states and crystalline structure, as well as morphology, phase composition, luminescence, and defects in ZnO rods grown as free-standing nanoparticles, was studied using a variety of experimental techniques. Mo has almost no influence on the luminescence of the grown ZnO particles, whereas shallow donors are strongly affected in ZnO rods. Annealing in air causes exciton and defect-related bands to drop upon Mo doping level. The increase of the Mo doping level from 20 to 30% leads to the creation of dominating molybdates. This leads to a concomitant drop in the number of formed ZnO nanorods. [ABSTRACT FROM AUTHOR]

Cesium lead bromide (CsPbBr 3 , CPB) powder formed by micro-, nanocrystals (MC, NC) and quantum dots (QD) was synthesized as free-standing and polystyrene covered. Luminescence was multicomponent, in general, ranging from below 1.9 eV up to about 2.6 eV. The ultrafast decay kinetics exhibited strong decay time component with the value of 260 ps. Electron paramagnetic resonance (EPR) revealed surface defects like O 2 − and some spin transitions most likely originating from some complex defect, supposedly F-V k (H) dimer center under the constant ultraviolet (UV) light irradiation at the temperature T = 10 K. The thermal release of the electrons from the O 2 − center was correlated with the 117 K thermally stimulated luminescence (TSL) peak. Coating with polystyrene resulted in the about doubly increased decay time of luminescence. The O 2 − and F-V k (H) EPR resonances were not observed as well. The TSL peak which might be ascribed to the O 2 − was not clearly detected anymore. The glow curve was composed of one very broad peak typical for the amorphous materials. At the same time, the polystyrene prevented the MCs creation. The existence of charge/energy transfer between the CPB and polystyrene due to the chemical bonding was assumed and confirmed also by calculations. [Display omitted] • EPR, TSL and RL study of charge trapping and luminescence in CsPbBr 3. • Charge/energy transfer was detected. • O 2 − -related electron trapping center was revealed in these crystals. • TSL peak was correlated to the release of electrons from the O 2 − surface center. • Complex bromine vacancy-related charge trapping center was observed. [ABSTRACT FROM AUTHOR]

In this study, a new Cs4SrI6:Yb2+,Sm2+ near‐infrared (NIR) emitting scintillator was developed using sensitization strategy. It was found that Yb2+ sensitization significantly enhances the NIR radioluminescence (RL) of Sm2+, providing a new approach of designing highly emissive sensitized NIR scintillators. By studying the optical spectra and decay kinetics of Cs4SrI6:Yb2+,Sm2+, it was revealed that the energy transfer pathways involve both radiative and nonradiative processes. The gamma spectroscopy performance of Cs4SrI6:Yb2+,Sm2+ single crystals was studied by using the high‐quantum‐efficiency avalanche photodiode (APD) as the readout. Our results highlight the importance of using sensitization strategy of achieving NIR emitting scintillators and demonstrate the significant potential for radiation detection applications. [ABSTRACT FROM AUTHOR]

Using single-crystal YAG:Ce plates with different dopant concentration under different sample temperatures (77-500(800)K), absorption, emission and luminescence decay characteristics were measured. Simulation is used to explain the luminescence decay time increase with growing temperature. For selected incident blue excitation band and given sample thickness the composed blue-yellow spectrum is calculated after passing through the sample. Temperature dependence of the color coordinates CIE-xy is calculated, arising mostly due to specific temperature dependence of the 4f-5d 1 absorption transition of Ce 3+ center in the garnet host. [ABSTRACT FROM AUTHOR]

We have investigated Li 4 SiO 4 scintillation crystals for their possible application in neutron detection due to high Li content and low density of 2.35 g/cm 3 . The micro-pulling-down method employing the Ir crucible and afterheater was optimized for crystal growth of Li 4 SiO 4 taking into account the Li evaporation. To grow high-quality crack-free single crystals, the heating power was increased to establish milder temperature gradient, thicker meniscus, smaller crystal diameter and resulting smaller stress in the as-grown crystals. The undoped, Ti-, Cr-, and Al- doped crystals were prepared and studied. Radioluminescence measurements under X-ray excitation showed quite high overall scintillation efficiency of the Ti-doped sample reaching as high as 250% of that of Bi 4 Ge 3 O 12 reference scintillator. The emission spectrum was dominated by one broad band peaking at 350 nm related to Ti 4+ impurity. Reasonable light yield of 10000 photons/neutron was found. However, its long decay time of 54 μs might be a limitation especially for high counting rate applications. The overall scintillation efficiency of the Cr 3+ sample was much lower and the spectrum shows one broad peak at 463 nm which does not correspond to Cr 3+ luminescence. The radioluminescence spectrum of the Al-doped sample resembled to that of the Ti-doped one, just its magnitude is considerably lower, which was explained by Ti contamination. Peculiarities and optimization of crystal growth and a preliminary sketch of luminescence mechanisms and dopant incorporation are discussed. [ABSTRACT FROM AUTHOR]

The role and effect of stable Ce^4+ centers in Ce-doped LuAG single crystal scintillator is further studied by means of measurements of several optical, luminescence and scintillation characteristics. Two LuAG:Ce single crystal samples are compared: in one of them the dominating Ce^4 + center is stabilized by high concentration Mg^2+ codoping while the other one shows only the presence of stable Ce^3 + center. Tailored (Eu, Mg)–doped LuAG single crystal is also prepared to test the presence and thermal stability of hole traps in the host which affect the timing characteristics of Ce^4+ scintillation cycle, namely its restoration back to 4+ charge state in last step of the cycle. EPR experiment was also employed at Mg- and (Eu, Mg) doped LuAG samples and the signature of the O^ - hole center stabilized by Mg^2 + ion was clearly obtained. [ABSTRACT FROM AUTHOR]

Ce-doped lutetium aluminum garnet Lu 3 Al 5 O 12 (LuAG) nanoceramics were fabricated at 1600 °C and 1700 °C by spark-plasma sintering (SPS) method from nano-powders prepared by radiation synthesis. Both undoped and Ce-doped LuAG ceramic samples were also prepared from the nano-powders at 1700 °C with significantly increased pre-heating rate. The backscattered electron images revealed large amount of pores in all the Ce-doped samples causing their significant opacity. On the other hand, very large grains and no pores were revealed in the undoped sample, which was the only transparent one. The radioluminescence measurements revealed superior overall scintillation efficiency of the samples sintered at the temperature 1700 °C, and their defect emission in the UV region was ascribed to oxygen-vacancy-related defects such as F + centers. The photoluminescence decay of the defect emission was characterized by an extremely fast decay time of a few nanoseconds. Influence of sintering procedure and subsequent annealing on the luminescence and scintillation properties is discussed. [ABSTRACT FROM AUTHOR]

Lutetium oxyorthosilicate Lu2SiO5 (LSO) and pyrosilicate Lu2Si2O7 (LPS) activated by Ce3+ or Pr3+ are known to be effective and fast scintillation materials for the detection of X-rays and γ-rays. Their performances can be further improved by co-doping with aliovalent ions. Herein, we investigate the Ce3+(Pr3+) → Ce4+(Pr4+) conversion and the formation of lattice defects stimulated by co-doping with Ca2+ and Al3+ in LSO and LPS powders prepared by the solid-state reaction process. The materials were studied by electron paramagnetic resonance (EPR), radioluminescence spectroscopy, and thermally stimulated luminescence (TSL), and scintillation decays were measured. EPR measurements of both LSO:Ce and LPS:Ce showed effective Ce3+ → Ce4+ conversions stimulated by Ca2+ co-doping, while the effect of Al3+ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr3+ → Pr4+ conversion was not detected by EPR, suggesting that the charge compensation of Al3+ and Ca2+ ions is realized via other impurities and/or lattice defects. X-ray irradiation of LPS creates hole centers attributed to a hole trapped in an oxygen ion in the neighborhood of Al3+ and Ca2+. These hole centers contribute to an intense TSL glow peak at 450–470 K. In contrast to LPS, only weak TSL peaks are detected in LSO and no hole centers are visible via EPR. The scintillation decay curves of both LSO and LPS show a bi-exponential decay with fast and slow component decay times of 10–13 ns and 30–36 ns, respectively. The decay time of the fast component shows a small (6–8%) decrease due to co-doping. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electron and hole trapping centers were observed in the molybdenum doped zinc oxide rods. • Electron trapping centers were mostly molybdenum-based. • Holes were trapped at oxygen complexes. • Exciton- and defect-related emission bands appear suppressed after X-ray irradiation. • Zinc vacancies participated in the charge trapping processes. Peculiarities of the point defects creation under X-ray irradiation and the influence of Mo doping in ZnO powders of nano- and microrods fabricated by the hydrothermal growth method (as-grown and annealed in air) were studied in detail. Correlated experiments of X-ray diffraction, X-ray photoelectron spectroscopy, electron paramagnetic resonance, photo- and radioluminescence as well as thermally stimulated luminescence allowed us to trace the effect of the molybdenum inclusion on the phase purity of synthesized materials and the role of Mo in the creation of X-ray induced point defects. Oxygen-based hole trapping centers (most probably involving interstitial oxygen) as well as Mo5+-based electron trapping centers were observed and their thermal stabilities were studied. Some amount of the hole trapping centers seemed to be directly connected with the creation of Mo5+. Zinc vacancies and the Mo5+ centers up to some extent were assumed to act as recombination centers for the holes released from the hole trapping centers. The X-ray irradiation also affects the luminescence properties of the ZnO:Mo samples – the intensity of the luminescence bands in general becomes weaker. [ABSTRACT FROM AUTHOR]

The properties of various inorganic scintillator materials with different origin of their VUV luminescence have been studied under pulsed excitation by XUV (50-1000 eV) synchrotron radiation. A comparison of spectral and timing characteristics of these crystalline VUV emitters has been performed. The processes of energy transfer from the host crystal to the luminescence centers of different nature were analyzed from the features of excitation spectra in the regions of inner-shell absorption. [ABSTRACT FROM AUTHOR]

Luminescence of new irregular Ce3+-related centers: the unperturbed and perturbed Ce3+ ions located in Al3+ sites and the CeLu3+ ions perturbed by LuAl3+ ions was found. The systematic stuffy of these centers by means of the ESR and luminescence methods and their influence on scintillation characteristics was performed. The structure and symmetry of the irregular Ce3+ centers was established and their spectral characteristics were explained. [ABSTRACT FROM AUTHOR]

Spectroscopic properties of Pb2+ in different fluoride host lattices were studied in order to investigate if Pb2+ can serve as a sensitizer for the Gd3+–Eu3+ quantum cutting system. Strong B′ emission of Pb2+ was found in several fluoride host lattices and for the first time B′ emission is reported at room temperature. It is shown that sensitization of the 6G levels of Gd3+ is possible via B′ emission of Pb2+ in the host lattice (BaF2)0.6(GdF3)0.4 and visible quantum cutting with an efficiency of 20% is observed upon excitation in the C band of Pb2+. The possibility of sensitization of Gd3+ by A′ emission of Pb2+ in KMgF3 is discussed. [Copyright &y& Elsevier]

We report on the behavior of InGaN/GaN multiple quantum well structure during excitation in UV-C and vacuum UV spectral region. Photoluminescence excitation spectra show peaks with positions different to the peaks in absorption spectra. The very high absorption coefficient in order of 107 cm−1 at energies above 6.9 eV causes the excitation in the surface region which enhances the non-radiative surface recombination. The mechanism explains the differences between absorption and excitation spectra measured in a studied range of energies between 5.8 and 40 eV. • Luminescence properties of InGaN/GaN structure were studied using UVC and VUV excitation. • The excitation spectra of the structure significantly differ from absorption spectra. • The difference is explained by dominant non-radiative surface recombination. [ABSTRACT FROM AUTHOR]

Glass ceramics in the form of MI 2 :Eu crystalline particles grown in MO-B 2 O 3 glass (M = Ca, Sr, Ba) through recrystallization from the alloyed melt were fabricated. Eu2+ ions were detected in the CaI 2 and SrI 2 crystalline particles (not in the BaI 2) inside the corresponding glasses. Some amount of Eu2+ centers are expected to originate from the MO-B 2 O 3 glass hosts as well. This was confirmed by correlated electron paramagnetic resonance (EPR), photo- and radioluminescence (PL, RL) measurements. Peculiarities of the Eu2+ distribution and incorporation into the glass ceramics samples as well as charge and energy transfer properties are discussed in detail. Optimal conditions leading to the enhancement of the Eu2+ emission from the CaI 2 and SrI 2 crystallites inside the glasses were determined. [ABSTRACT FROM AUTHOR]

For the first time, hafnia (HfO2) nanoparticles have been produced by photochemical synthesis. The photochemical route has been proven to be scalable, affordable, and straightforward to create monoclinic HfO2 nanoparticles with a size of tens of nanometers. The exploitation of this route offers a chance to create large amounts of dense nanoparticles with reduced costs and time of production for future creation of large area composite scintillators for fast timing techniques. Specific annealing treatments from 450 °C to 1000 °C have been targeted to tune the structural and morphological properties and optimize the luminescence of the nanoparticles. Hafnia nanoparticles annealed at low temperature display an amorphous structure. After thermal treatment at 1000 °C, HfO2 nanoparticles crystallize into a monoclinic phase, as evidenced by thermal analyses and X-ray diffraction. Radioluminescence and photoluminescence of HfO2 have been investigated at room temperature and 77 K. The emission band of hafnia covers a range from 300 to 600 nm and it can be attributed to defects within the matrix. In particular, the highest radioluminescence intensity appears in the crystalline sample annealed at 1000 °C, thanks to the higher crystallinity degree and the reduction of non-radiative channels and quenching defects. Photoluminescence and scintillation decay have evidenced the presence of the fast decay in the nanosecond time range. Thus, due to their size, density, and spectroscopic and timing features, monoclinic hafnia nanoparticles obtained by photochemical synthesis are attractive for potential creation of large area scintillating composites. [ABSTRACT FROM AUTHOR]

A comprehensive study of the optical, radioluminescence and scintillation properties of both the Lu 3+ rich and Lu 3+ deficient non-stoichiometric Lu 3+x AG:Ce,Mg (Lu 3+x Al 5 O 12 :Ce,Mg, x = −4, −1, +1 and +4 at.%) ceramics are performed, completed further by the microstructure and defects characterization. Small deviation from the stoichiometric composition as well as Mg 2+ codoping plays a crucial role in ceramic transparency, radioluminescence intensity and the timing characteristics of scintillation response. The Lu Al antisite defects could be suppressed efficiently by controlling Lu 3+ content below stoichiometry of LuAG host. MgO (Mg 2+ ions) as effective sintering aids, can improve both the optical quality and scintillation performance (light yield, scintillation decay times and the ratio of fast decay components). We generally discuss the composition dependence of defects and properties tailoring. We also performed the systematic comparative study with the stoichiometric LuAG:Ce,Mg ceramic and the commercial BGO and LuAG:Ce single crystals. [ABSTRACT FROM AUTHOR]

Lu 3−x Al 5 O 12 :Ce optical ceramics (Lu 3−x AG:Ce, x = 1, 2, 3 and 4 at.%, respectively) with Lu 3+ compositions ranging from 1 to 4 at.% below stoichiometry content were fabricated by solid state reaction method and further optimized by an air-annealing process. The effect of Lu 3+ deficiency on the optical, luminescence and scintillation properties of such a non-stoichiometric Lu 3−x Al 5 O 12 :Ce ceramics was investigated. Significant influence in the material densification was found leading to strong changes in the transparency, radioluminescence (RL) and scintillation response of these ceramics. Within the range of 1–4 at.% Lu 3+ deficiency, Lu Al antisite defects were suppressed effectively and the Lu 3−x AG:Ce ceramics displayed an extremely high RL intensity which reaches ∼4 times higher than that of the latest commercial LuAG:Ce single crystals while its transparency deteriorated. The microstructure, presence of foreign phases and charge traps acting in scintillation mechanism were also characterized by means of SEM, back scattered electron imaging and thermoluminescence techniques, respectively. [ABSTRACT FROM AUTHOR]

The influence of the Mg 2+ codoping and annealing in the air on the scintillation and luminescence characteristics of Pr-doped lutetium-aluminum garnet crystals (LuAG) was studied to find a possible positive effect of Pr 4+ . The overall scintillation efficiency under X-ray excitation of the annealed Pr- doped samples decreased with increasing Mg concentration. This was explained by increased overlap of the Pr 3+ 5d-4f emission with the charge-transfer (CT) absorption band of the Pr 4+ ion stabilized by Mg 2+ . This absorption caused even greater decrease of the light yield, as the light is collected from the whole sample volume in the pulse-height spectrum measurement. Electron centers based on oxygen vacancies (F + centers) which can have negative influence on scintillation mechanism were revealed by the electron paramagnetic resonance (EPR) experiments. The O - hole center was detected as well and the temperature dependences of the EPR spectra showed that its thermal stability was decreased by Mg codoping. Negligible changes in the decay time of Pr 3+ 5d-4f photoluminescence exclude the non-radiative energy transfer from relaxed 5d 1 excited state of Pr 3+ towards CT absorption transition of Pr 4+ and suggest that simple reabsorption of the emitted light takes place. Unlike for the Ce-doped analogs, promoting the Pr 3+ luminescence center to the tetravalent state by divalent ion co-doping and air annealing did not improve scintillation properties of Pr-doped LuAG. [ABSTRACT FROM AUTHOR]

The Nd-doped, Gd-doped and doubly Nd, Gd-codoped BaLu 1.2 Y 0.8 F 8 (BaLuYF) and LuF 3 single crystals were grown by a micro-pulling-down method. Their photoluminescence, radioluminescence and alpha-ray-excited pulse-height spectra were studied in the vacuum-ultra-violet (VUV) region to confirm their possible application as fast VUV scintillators. Complementary photoluminescence measurements in the ultra-violet/visible spectral region were performed as well. The possibility of scintillation performance improvement by Gd codoping was tested. The overall scintillation efficiency of BaLuYF:Nd1% was comparable to that of the LaF 3 :Nd8% reference sample and only slight improvement was observed after Gd1% codoping. The positive effect of Gd codoping was confirmed for higher dopant concentrations. This was explained by an energy transfer from the high-energy Gd 3+ 4f 2 G(0) 7/2 level to the Nd 3+ 5d state. On the other hand, pulse-height spectra showed degradation of the light yield under alpha-ray excitation, which was explained by introduction of slow components due to Gd codoping. On the other hand, no positive effect of Gd codoping was found for the overall scintillation efficiency of Nd-doped LuF 3 , despite the same energy transfer process was confirmed. Slight improvement of the light yield under alpha-ray excitation was confirmed. [ABSTRACT FROM AUTHOR]

The glass‐ceramics (GC) of gadolinium aluminum gallium garnets with the expected composition of Gd3Al3Ga2O12:Ce and Gd3Al3Ga2O12:Ce,Be (GAGG:Ce and GAGG:Ce,Be, respectively) are fabricated by crystallization from the Gd2O3–Al2O3–Ga2O3–CeO2–SiO2–BeO (Gd:Ga:Al ratio is close to 3:2:3) glasses. The influence of Be2+ co‐doping (including doping level) on the luminescent properties of the GAGG is demonstrated. In particular, Be co‐doping results in the suppression of the Ce3+‐related radioluminescence (RL) and as a consequence, the light yield is lowered as well. The conclusion is made that Be2+ creates effective electron or hole trapping centers. [ABSTRACT FROM AUTHOR]

Low‐dimensional perovskite halides have shown a great potential as X‐ray detection materials because of efficient exciton emissions originating from strongly spatially localized charge carriers. Nonetheless, most of them have a scintillation yield far below their theoretical limits. Here, it is found that the harvesting efficiency of produced charge carriers can be significantly enhanced via a small amount of In+ doping in these highly localized structures. A bright and sensitive zero‐dimensional Cs3Cu2I5:In+ halide with efficient and tunable dual emission is reported. The radioluminescence emission of Cs3Cu2I5:In+ crystals under X‐ray excitation consists of a self‐trapped exciton emission at 460 nm and an In+‐related emission at 620 nm at room temperature. In+ doping enhances the photoluminescence quantum efficiency (PLQY) of Cs3Cu2I5 from 68.1% to 88.4%. Benefiting from the higher PLQY, Cs3Cu2I5:In+ can achieve an excellent X‐ray detection limit of 96.2 nGyair s−1, and a superior scintillation yield of 53 000 photons per MeV, which is comparable to commercial CsI:Tl single crystals. As a result, a remarkable X‐ray imaging resolution of 18 line pairs mm–1 is demonstrated, which is so far a record resolution for single crystal perovskite‐based flat‐panel detectors. These results highlight the importance of efficient harvesting of carriers (and excitons) in low‐dimensional perovskites for radiation detection applications. [ABSTRACT FROM AUTHOR]

Driven by the pursuit of optimizing the luminescent properties of garnet-based single crystals for X-ray imaging applications, this work reports on the successful synthesis and in-depth characterization of GYAGG crystals doped with Ce³⁺ or Tb³⁺ ions, and doubly-doped with both of them. Micro-pulling down synthesis yielded crystals with a single cubic phase confirmed by X-ray diffraction. Photoluminescence (PL) and radioluminescence (RL) measurements on Ce³⁺,Tb³⁺ co-doped GYAGG revealed bidirectional energy transfer processes. Characteristic broadband 5d 1 →4f emission of Ce³⁺ centers peaking at 530 nm and narrow 4f→4f emission lines of Tb³⁺ ions starting from 5D 4 level within 480–630 nm were observed. At higher doping levels, cross-relaxation in Tb³⁺ pairs resulted depleted 5D 3 state and only the emission from 5D 4 one was observed in the spectra. Analysis of PL decay characteristics corroborated the spectral observations, confirming progressively decreasing Ce³⁺ decay time (down to 40 ns at 15 % Tb3+) due to enhanced Ce³⁺→Tb³⁺ energy transfer. Similarly, the Tb³⁺ decay time accelerated by more than 60 % after the Ce³⁺ co-doping. Notably, co-doping with 0.5 % Ce³⁺ and 10–15 % Tb³⁺ doubled the luminescence intensity of RL spectra compared to 0.5 % Ce³⁺-doping alone, attributed to the increased density of emitting centers. • High-quality and crack-free GYAGG:Ce,Tb single crystals were successfully grown. • The photoluminescence spectra revealed Ce³⁺↔Tb³⁺ bidirectional energy transfer. • At lower Tb³⁺ doping (0.5 %), the bidirectional energy transfer was inefficient. • High Tb³⁺ doping (15 %) significantly enhanced energy transfer. • Co-doping yielded a two-fold radioluminescence intensity compared to sole doping. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present the photoluminescence (PL) and scintillation response of Pr3+-doped Y3Al5O12 (YAG:Pr) single crystals grown by the Czochralski method with different Pr3+ concentrations of 0.16, 0.33, and 0.65 mol%. PL spectra and decay curves were measured for both the fast 5d → 4f and slow 4f → 4f emissions. The PL decay times were evaluated which evidence concentration quenching especially in 1D2 → 3H4 emission for the highest Pr3+ concentration. Light yield (LY) of 15,600 photons per MeV and energy resolution of 6.4% at 662 keV γ-rays were obtained with the YAG:Pr (0.33%) crystal. The LY non-proportionality and energy resolution versus γ-ray energy were measured and the intrinsic resolution was calculated. A good proportionality of the LY was found within 7% over the energy range from 1274.5 keV down to 32 keV. The estimated photofraction in the pulse height spectra of 320 and 662 keV γ-rays was also determined and compared with the theoretical one calculated using WinXCom program. [Copyright &y& Elsevier]

Abstract: 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 La2O3 and Sc2O3 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 Pr3+ fast 5d–4f luminescence intensity. The aspects of energy transfer and trapping due to sintering aids in LuAG lattices are discussed. [Copyright &y& Elsevier]

The compositional dependence of luminescence properties and scintillation response were investigated in Ce3+-doped Y2Gd1Al5-xGaxO12 (x=2, 3, 4) single crystals. The Gd3+ → Ce3+ energy transfer was evidenced by photoluminescence excitation spectra of Ce3+ emission. With increasing Ga content in the garnet host, the Ce3+ luminescence from the lowest 5d level (5d1) is shifted toward higher energy due to the decrease in the crystal field splitting of the 5d levels. Light yield (LY) and its dependence on the amplifier shaping time were measured under excitation with γ-rays High LY value of ~38 000 ph/MeV was obtained for a Y2Gd1Al5-xGaxO12:Ce sample. Scintillation decay was measured with an extended dynamical and temporal scale under the nanosecond pulse soft X-ray excitation. The decrease of both LY value and relative contribution of slower decay component in the scintillation response was observed with increasing Ga content in the garnet host. [ABSTRACT FROM AUTHOR]

Luminescence and scintillation properties of Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,Mg (0.02, 0.05 %) garnet crystals grown by the micro-pulling down method were investigated. The onset temperature for luminescence quenching at ∼365 K is determined from the temperature dependence of photoluminescence decay time. At room temperature, the Mg (0.05 %) sample exhibits high integral scintillation efficiency of ∼445 % of BGO crystal, light yield value of 23,500 photons/MeV, and fast scintillation decay times of 20 ns (15 %) + 54 ns (85 %). The higher radioluminescence intensity of the Mg (0.05 %) sample correlates with an appearance of its lower themally-stimulated luminescence intensity in 77–500 K range. • Luminescence and scintillation properties of Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,Mg (Mg = 0.02 %, 0.05 %) crystals are investigated. • Both crystals show onset of luminescence quenching at 365 K. • Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,0.05%Mg shows light yield of 23,500 photons/MeV. • Lu 2 YAl 2.5 Ga 2.5 O 12 :Ce,0.05%Mg shows scintillation decay time of 20 ns (14 %) + 54 ns (86 %). • Thermoluminescence characteristics are investigated. [ABSTRACT FROM AUTHOR]

The scintillation characteristics of Lu0.8Gd2.2 (Al5–xGax)O12:Ce,Mg (x = 2.6 and 3) single crystals grown by the micropulling down method are investigated. The light yield of 27600 photons/MeV obtained for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg is higher than that of 25 400 photons/MeV obtained for Lu0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. The photoluminescence and scintillation decays measured at room temperature (RT) for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg are faster than those for Lu0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. Temperature dependence of radioluminescence (RL) intensity indicates a lower quenching temperature for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg. Coincidence time resolution of a Lu0.8Gd2.2Al2Ga3O12:Ce,Mg detector in coincidence experiment with a BaF2 detector was measured to be 410 ps. The afterglow and thermally stimulated luminescence (TSL) characteristics below RT are also measured. [ABSTRACT FROM AUTHOR]

The scintillation characteristics of Gd 3 Al 2 Ga 3 O 12 :Ce, Li (GAGG:Ce,Li) and Gd 3 Al 2 Ga 3 O 12 :Ce, Mg (GAGG:Ce,Mg) single crystals were compared. Radioluminescence spectra and photoluminescence decay curves were measured at various temperatures between 77 and 500 K to investigate the thermal luminescence quenching. At 662 keV γ rays, the LY value of 35,400 photons/MeV and energy resolution of 6.9% obtained for GAGG:Ce, Li are superior to those of 24,200 photons/MeV and 9.5% for GAGG:Ce,Mg. Scintillation decays are approximated by a double exponentials with a fast principal decay component of 47 ns (83%) for GAGG:Ce, Mg and 90 ns (86%) for GAGG:Ce,Li. Coincidence time resolution of 282 ps obtained for GAGG:Ce, Mg is better than that of 389 ps for GAGG:Ce,Li. GAGG:Ce, Mg shows a much lower afterglow and thermally stimulated luminescence intensity with respect to GAGG:Ce,Li. • Scintillation properties of Li+ and Mg2+ -codoped Gd 3 Al 2 Ga 3 O 12 :Ce are compared. • Gd 3 Al 2 Ga 3 O 12 :Ce, Mg exhibits better timing performance. • Gd 3 Al 2 Ga 3 O 12 :Ce, Mg shows lower afterglow and TSL intensity. • Gd 3 Al 2 Ga 3 O 12 :Ce, Li exhibits high light yield and good energy resolution. [ABSTRACT FROM AUTHOR]

Abstract Ce:(Gd,La) 2 Si 2 O 7 (Ce:La-GPS) and Al co-doped Ce:(Gd,La) 2 Si 2 O 7 (Al,Ce:La-GPS) single crystals were grown by the micro-pulling-down method to improve the mechanical, optical and scintillation properties. In a tensile test, the maximum strain and stress values in the stress-strain curve of the Al,Ce:La-GPS single crystal compared to the Ce:La-GPS single crystal and the result suggests that there is a possibility of the improvement on the mechanical property by Al co-doping. In addition, the light yield of the La-GPS single crystal under γ-ray irradiation was slightly increased and the decay time was accelerated by the Al co-doping. Highlights • Al co-doped Ce:La-GPS single crystals were grown by the μ-PD method. • It is a possibility that Al co-doping improves the mechanical property of the La-GPS. • Emission peaks originated from 5 d-4f transitions of the Ce3+ ion were observed. • The light yield under γ-ray irradiation was slightly increased by Al co-doping. • Scintillation decay times were accelerated by Al co-doping. [ABSTRACT FROM AUTHOR]

Europium-doped lutetium oxide (Eu:Lu 2 O 3 ) nano-powders were synthesized by a co-precipitation method from europium and lutetium nitrates using ammonium hydrogen carbonate (AHC) as the precipitant. Fine and low-agglomerated powders with average particle size of 68 nm were obtained by calcining the precursor at 1100 °C for 4 h. Using this powder as starting material, Eu:Lu 2 O 3 transparent ceramics with the average grain size of ∼46 μm were fabricated by vacuum sintering at 1650 °C for 30 h, whose in-line transmittance reaches 66.3% at 611 nm. The influences of air annealing on optical transmittance, decay time, spectroscopic properties, light output and thermally stimulated luminescence of Eu:Lu 2 O 3 ceramics were investigated in detail. Based on radioluminescence spectra, the light output of the annealed Eu:Lu 2 O 3 ceramics is 10 times higher than that of the commercially available BGO single crystal, and it indicates that transparent Eu:Lu 2 O 3 scintillation ceramics is a promising candidate for X-ray radiation detectors. [ABSTRACT FROM AUTHOR]

Optical properties of yttria-aluminoborate (YAB) glasses with general composition 10(Ce x Tb y Y (1-x-y) )-30Al 2 O 3 -60B 2 O 3 are investigated and compared with data available on YAB crystals with huntite-like structure. Ce doped samples show optical features ascribable to preferential location of rare earth ions in sites with specific geometry similar to that observed in crystalline structures. Samples prepared with Tb ions as emission activator and Ce ions as sensitizer have been studied within the framework of non-radiative energy transfer. The resulting Förster radius is of 4.6 ± 0.5 Å comparable with that observed in Ce/Tb co-doped YAl 3 (BO 3 ) 4 crystals. The investigated materials possess radio- and photoluminescence emission efficiencies and performances comparable to that of crystalline counterparts with the advantage of having easiness of preparation and workability typical of glassy systems. [ABSTRACT FROM AUTHOR]

Ytterbium doped scandium oxide (Yb:Sc 2 O 3 ) transparent ceramics were fabricated by a co-precipitation and vacuum sintering method. The characteristics of the precursor and the calcined powders were investigated by BET, XRD, and SEM. Ultra-fine and low agglomerated 5at%Yb:Sc 2 O 3 powders with the average particle size about 65.4 nm were obtained after calcined at 1100 °C for 5 h. Using the synthesized powders as starting materials, 5at%Yb:Sc 2 O 3 transparent ceramics with the in-line transmittance of 71.1% at 1100 nm and average grain size of 145 μm were fabricated by vacuum sintering at 1825 °C for 10 h. Quasi-CW laser oscillation of Yb:Sc 2 O 3 ceramics was obtained at 1040.6 nm. A maximum output power as high as 2.44 W with a corresponding slope of 35% was achieved. Finally, the tunability of the ceramic was explored measuring a tuning range up to 55 nm. [ABSTRACT FROM AUTHOR]

We report the first laser oscillations of 5 at %, 10 at % and 20 at % Yb 3+ doped LuYAG ceramic samples and their spectroscopic characterization. The maximum output power, 8.7 W at 1029 nm, is achieved by 10 at % sample. A slope efficiency as high as 90.1% is obtained from the 10 at % doped sample. To our knowledge, these are the highest laser slope efficiencies obtained so far for Yb 3+ doped LuYAG ceramics. With the 20 at % doped ceramic the maximum output power was 7.2 W at 1047.6 nm with a corresponding slope efficiency of 47.4%, whereas a decrease of the output power is observed for absorbed pump power higher than 15.6 W, probably due to the appearance of a non-linear loss mechanism. Finally, we explored the tunability of the ceramics finding the broadest continuous tuning range (from 992 nm to 1060 nm, i.e. 68 nm), with 5 at % and 10 at %, while it decreases to 54 nm with 20 at %. [ABSTRACT FROM AUTHOR]

Ce3+,Pr3+-codoped SiO2-Al2O3-B2O3-Gd2O3 glasses (SABG:Ce,Pr) were prepared by melt quenching under a CO reducing atmosphere. Luminescence properties were investigated under UV and X-ray excitations. A dominant emission band at 430 nm belonging to the Ce3+:5d1 → 4f transition was observed in the photo- and radio-luminescence spectra. The energy transfer occurs from this Ce3+ band toward the 3PJ levels of Pr3+ with an efficiency of up to 24%, followed by the reduction of integrated luminescence intensity with an increasing Pr3+ concentration. This result is attributed to the increase in the reabsorption of Ce3+ luminescence and the non-radiative energy transfer toward the 3PJ levels of Pr3+. The cross-relaxation process within the Pr3+ pairs can further diminish the total luminescence yield at high Pr3+ concentrations. The integral scintillation efficiency and light yield measurements were carried out and compared to the reference Bi4Ge3O12 (BGO) crystal. [ABSTRACT FROM AUTHOR]

Cerium doped gadolinium gallium aluminum garnet (Gd 3 Al 3 Ga 2 O 12 , GAGG) was synthesized in the glass ceramics form by the crystallization from Gd 2 O 3 –Al 2 O 3 –Ga 2 O 3 –SiO 2 –CeO 2 glass in the following weight proportion: 101 : 26: 47 : 25: 1. The spatial distribution and incorporation of Ce into the GAGG ceramic grains as well as the luminescence and scintillation performance are studied carrying out correlated experiments of photo-, radio- and cathodoluminescence including decay kinetics as well as energy dispersive X-ray spectroscopy combined with scanning electron microscopy. Optical absorption features were investigated using photothermal deflection spectroscopy. Cerium stays within the material mostly in the Ce3+ charge state. Its distribution in the bulk of the sample exhibits irregular trend indicating the tendency to coalesce in the middle. • The GAGG:Ce glass nanoceramics was fabricated. • Spatial distribution of Ce3+ in the batch of the glass nanoceramics was observed. • Hole trapping processes affect the luminescence in GAGG:Ce glass nanoceramics. [ABSTRACT FROM AUTHOR]

The In-doped LiCaAlF 6 [In:LiCAF] single crystals were grown by the micro-pulling-down (μ-PD) method, and the phases, chemical compositions, transmittance and radioluminescence spectra were investigated. All the grown crystals showed high transparency and single phase of LiCAF without visible cracks and inclusions except for the end part of In2%:LiCAF crystal which included the impurity phase. In the radioluminescence spectra of the In:LiCAF crystals under X-ray irradiation, the emission peak around 750 nm was revealed. [ABSTRACT FROM AUTHOR]

Monovalent Li + codoped Lu 3 Al 5 O 12 :Ce (LuAG:Ce) optical ceramics were fabricated by solid state reaction method and further optimized by an air-annealing process. Optical absorption, radioluminescence spectra and scintillation properties such as light yield, scintillation decay times and afterglow were measured and compared with those of the Li + free LuAG:Ce ceramic and the commercial LuAG:Ce single crystal samples. Positive effect of Li + codopant consists mainly in the significant increase of scintillation light yield, acceleration of scintillation decay as well as the decrease of afterglow intensity. With 0.3% Li codoping, the obtained LuAG:Ce,Li ceramic displays a light yield of ∼29200 ph/MeV at 10 μs shaping time, higher than that of the LuAG:Ce single crystal and optical ceramic scintillators ever reported. The partial conversion of the stable Ce 3+ to Ce 4+ centers and the shallow and deep traps effect suppression by the Li + codoping are discussed. [ABSTRACT FROM AUTHOR]

Optical and scintillation characteristics of Mg2+-codoped Lu 2 Y(Al 5-x Ga x)O 12 :Ce (x = 2, 3) multicomponent garnet crystals grown by the micro-pulling down method were investigated. At RT, the shortening of scintillation decay time and a decrease of light yield (LY) value measured for a higher Ga containing samples can be explained by thermal ionization of the Ce3+ 5d 1 excited state. At 662 keV γ-rays, Lu 2 YAl 3 Ga 2 O 12 : Ce, 0.05%Mg exhibits high LY value of 29,000 ph/MeV along with scintillation decay times of 50 ns (86%) + 73 ns (14%). Co-doping with larger Mg2+ content leads to a decrease of LY value, scintillation decay time, and afterglow level. Radioluminescence quenching observed at low temperature region in correlation with large thermoluminescence peaks can be caused by trapping of electrons at intrinsic shallow traps. • Luminescence and scintillation properties of Lu 2 Y(Al 5-x Ga x)O 12 :Ce,Mg (x = 2, 3) crystals are investigated. • Temperature dependencies of photo-and radioluminescence are presented. • Lu 2 YAl 3 Ga 2 O 12 :Ce,0.05%Mg shows high light yield of 29,000 photons/MeV. • Lu 2 YAl 3 Ga 2 O 12 :Ce,0.05%Mg shows quenching temperature at 435 K due to thermal ionization. • Afterglow and thermoluminescence characteristics are investigated. [ABSTRACT FROM AUTHOR]

Mg2+-codoped Y 0.6 Gd 2.4 Al 2 Ga 3 O 12 :Ce (YGAGG:Ce,Mg) single crystal was grown by the Czochralski method and its luminescence and scintillation properties were investigated. Temperature dependence of radioluminescence (RL) yield and photoluminescence (PL) decay time was measured, and activation energy of thermal ionization process was determined from temperature-dependent PL decay time measurement. YGAGG:Ce,Mg exhibited high X-ray excited RL yield almost 5 times higher than BGO reference scintillator. Its light yield of 41,500 ph/MeV and scintillation decay times of 12 ns (2%) + 52 ns (65%) + 207 ns (33%) were measured under excitation with 662 keV γ rays from 137Cs source. Afterglow and thermally stimulated luminescence characteristics are also investigated. • Luminescence and scintillation properties of Y 0.6 Gd 2.4 Al 2 Ga 3 O 12 :Ce,Mg crystal are investigated. • Temperature dependence of photo-and radioluminescence are presented. • Y 0.6 Gd 2.4 Al 2 Ga 3 O 12 :Ce,Mg shows high light yield of 41,500 photons/MeV. • Luminescence quenching above RT can be caused by thermal ionization. • Afterglow and thermoluminescence characteristics are investigated. [ABSTRACT FROM AUTHOR]

The ns 2 -type metal elements (Pb and Sn) doped LiCaAlF 6 single crystals were grown by a micro-pulling-down (μ-PD) method. Pb doped LiCaAlF 6 [Pb:LiCAF] crystals showed high transparency and single phase of the LiCAF structure. However, we could not obtain Sn:LiCAF crystals due to the evaporation of SnF 2 during the crystal growth. There was an absorption peak around 193 nm in the transmittance spectrum of Pb:LiCAF crystal. In the radioluminescence spectrum of the Pb:LiCAF crystal under X-ray irradiation, two emission peaks around 200 and 830 nm were observed. [ABSTRACT FROM AUTHOR]

Dy3+-doped oxide glass with 30 mol.% Gd2O3 content in the glass host was prepared by melt quenching under CO reducing atmosphere. The luminescence properties were investigated under UV and X-ray excitation. The 4F9/2→6H J ( J = 15/2, 13/2, 11/2, and 9/2) luminescence was observed with intense blue (484 nm; 4F9/2→6H15/2) and yellow (576 nm; 4F9/2→6H13/2) emissions. Energy transfer from Gd3+ to Dy3+ ions was confirmed by photoluminescence excitation and emission spectra as well as photoluminescence decay measurements. The integral scintillation efficiency of 11% of Bi4Ge3O12 scintillator was obtained. [ABSTRACT FROM AUTHOR]

The optical and scintillation properties of Ce 3+ -doped YGd 2 Al 5− x Ga x O 12 ( x =2,3,4) single crystals were investigated. With increasing Ga content in the garnet host, the 5d 1 absorption and emission bands shift toward higher energy due to the decrease in the crystal field splitting of the 5d levels. Temperature dependences of absorption and emission spectra and of photoluminescence decays of both prompt and delayed components were measured. Light yield (LY) and its dependence on an amplifier shaping time were measured under excitation with γ-rays. High LY value of 38,000 photons/MeV was obtained for a YGd 2 Al 2 Ga 3 O 12 :Ce sample. Scintillation decay was measured with an extended dynamical and temporal scale under the nanosecond-pulsed soft X-ray excitation. The relative content of the fastest component in the scintillation response increases with increasing Ga content. [ABSTRACT FROM AUTHOR]

The development of plastic scintillators loaded with low-cost phosphorescent sensitizer is currently an important topic toward enhancing the scintillation light yield for radiation detection applications. In this work, we report plastic scintillators loaded with deep-blue-emitting phosphorescent sensitizer CuI(PPh 3) 2 (t -BuPy), where PPh 3 and t -BuPy stand for triphenylphosphine and 4- tert -butylpyridine, respectively. CuI(PPh 3) 2 (t -BuPy)-loaded poly(vinyltoluene)-based plastic scintillators with high optical transmittance of over 80% were synthesized via bulk polymerization method. The optical absorption, photoluminescence spectra, decay kinetics, and scintillation performance under X-ray, γ-ray, and α-particle excitation were comprehensively investigated. The scintillation yield was reduced with the increase of CuI(PPh 3) 2 (t -BuPy) loading concentration. The physical mechanism and the role of the copper iodide complex in scintillation yield reduction are proposed. [Display omitted] • Poly(vinyltoluene)-based plastic scintillators loaded with phosphorescent sensitizer CuI(PPh 3) 2 (t -BuPy) were synthesized. • The scintillation yield of PVT scintillators is reduced with the increase of CuI(PPh 3) 2 (t -BuPy) loading concentration. • The scintillation yield reduction is associated with the nonradiative dissipation of energy from CuI(PPh 3) 2 (t -BuPy). • Plastic scintillator containing only CuI(PPh 3) 2 (t -BuPy) showed α/γ PSD performance. [ABSTRACT FROM AUTHOR]

Lead halide perovskite nanocrystals of the formula CsPbBr3 have recently been identified as potential time taggers in scintillating heterostructures for time-of-flight positron emission tomography (TOF-PET) imaging thanks to their ultrafast decay kinetics. This study investigates the potential of this material experimentally. We fabricated CsPbBr3 thin films on scintillating GGAG:Ce (Gd2.985Ce0.015Ga2.7Al2.3O12) wafer as a model structure for the future sampling detector geometry. We focused this study on the radioluminescence (RL) response of this composite material. We compare the results of two spin-coating methods, namely the static and the dynamic process, for the thin film preparation. We demonstrated enhanced RL intensity of both CsPbBr3 and GGAG:Ce scintillating constituents of a composite material. This synergic effect arises in both the RL spectra and decays, including decays in the short time window (50 ns). Consequently, this study confirms the applicability of CsPbBr3 nanocrystals as efficient time taggers for ultrafast timing applications, such as TOF-PET. [ABSTRACT FROM AUTHOR]

The sensitization of scintillation was investigated in crosslinked polymeric composite materials loaded with luminescent gold clusters aggregates acting as sensitizers, and with organic dye rhodamine 6G as the emitting species. The evolution in time of the excited states population in the systems is described by a set of coupled rate equations, in which steady state solution allowed obtainment of an expression of the sensitization efficacy as a function of the characteristic parameters of the employed luminescent systems. The results obtained indicate that the realization of sensitizer/emitter scintillating complexes is the strategy that must be pursued to maximize the sensitization effect in composite materials. [ABSTRACT FROM AUTHOR]

Luminescence and scintillation characteristics of Mg2+-codoped (Lu x Gd 3-x)Al 2.4 Ga 2.6 O 12 :Ce (x = 0.2–0.8) garnet crystals grown by the micro-pulling down method are investigated. The Ce3+ 5d 1 → 4f luminescence is blue-shifted with increasing Lu content due to the decrease in crystal field splitting of the 5 d levels. With increasing Lu content, the shortening of scintillation decay time accompanied with a decrease of LY value as measured at room temperature can be explained by thermal ionization of the Ce3+ 5d 1 excited state. Co-doping with Mg2+ results in the shortening of scintillation decay time, the reduction of LY value and afterglow intensity. At low temperature the radioluminescence quenching is observed in correlation with large thermoluminescence peaks, which can be attributed to the localization of electrons at intrinsic shallow traps. • Luminescence and scintillation of (Lu,Gd) 3 Al 2.4 Ga 2.6 O 12 :Ce, Mg crystals are investigated. • Temperature dependence of photo-and radioluminescence are presented. • Luminescence quenching above RT can be caused by thermal ionization. • Afterglow and low-temperature TL characteristics are investigated. [ABSTRACT FROM AUTHOR]

Ce-doped Gd3Al3Ga2O12 (Ce:GAGG) crystal shows good scintillation performances, especially high light yield. However, its scintillation decay contains slower components. Such phenomenon is due to the delayed radiative recombination process which is caused by trapping effects in the transport stage of scintillation mechanism. Various defects including oxygen vacancy can give rise to shallow traps in the forbidden gap of the material which can cause such phenomena. To study the influence of such oxygen defects, 0.2-mol% Ce-doped GAGG single crystals were grown by Floating Zone method using growth atmosphere with different oxygen concentrations. The optical and scintillation properties of the crystals were examined. The light yield and emission wavelength of these samples did not depend on the oxygen content in the growth atmosphere. On the other hand, scintillation decays of the samples grown under the high oxygen concentrations (100 and 40% oxygen) were faster than that of the sample grown under the lower concentration (20%). Oxygen content in the growth atmosphere thus appears an important parameter in the optimization of the growth process of these materials (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Information on localization of Al in tea leaf tissues is required in order to better understand Al tolerance mechanism in this Al-accumulating plant species. Here, we have used low-energy X-ray fluorescence spectro-microscopy (LEXRF) to study localization of Al and other low Z-elements, namely C, O, Mg, Si and P, in fully developed leaves of the tea plant [ Camellia sinensis (L.) O. Kuntze]. Plants were grown from seeds for 3 months in a hydroponic solution, and then exposed to 200 μM AlCl for 2 weeks. Epidermal-mesophyll and xylem phloem regions of 20 μm thick cryo-fixed freeze-dried tea-leaf cross-sections were raster scanned with 1.7 and 2.2 keV excitation energies to reach the Al-K and P-K absorption edges. Al was mainly localized in the cell walls of the leaf epidermal cells, while almost no Al signal was obtained from the leaf symplast. The results suggest that the retention of Al in epidermal leaf apoplast represent the main tolerance mechanism to Al in tea plants. In addition LEXRF proved to be a powerful tool for localization of Al in plant tissues, which can help in our understanding of the processes of Al uptake, transport and tolerance in plants. [ABSTRACT FROM AUTHOR]