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A set of samples based on InGaN/GaN multiple quantum well (QW) structures with an extremely thick active region and high QW numbers was prepared on different substrates by metal organic vapor phase epitaxy. Their morphology was studied by SEM images, and their optical properties, including photoluminescence (PL) excitation, PL emission spectra, and PL decay curves, were measured by means of time-resolved luminescence spectroscopy. The obtained spectral features were tentatively explained by using the band scheme, which is commonly used for the description of InGaN/GaN multiple QW (MQW) structures. The application potential in the field of nanoscintillators used for fast timing of studied structures is discussed as well.

We report the study of the fast rise time and decay time in the ps time scale of the excitonic luminescence of a multiple quantum well (MQW) heterostructure of InGaN/GaN, including the excitation density effect. These structures were proposed as ultrafast scintillators for soft X-ray detectors and particle beam diagnostics. Measurements were carried out with a Hadland Imacon 500 streak camera following excitation of the sample by laser pulses of few tens of µJ at 266 nm and 400 nm, with pulse duration less than 200 fs. The rise time of the detected MWQ luminescence was less than 10 ps, with a possible contribution from the detection system and signal collection geometry. The calibration and the signal processing techniques employed to fully exploit the time resolution of the detection system are also described.

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.

The indirect photochemical synthesis for the preparation of bandgap- or defect-engineered multicomponent garnet powders from aqueous solutions was investigated. Gd3(Ga,Al)5O12 (GGAG) doped with Ce or Ce + Eu and Lu3(Al,Sb)5O12 doped with Eu were produced by calcination of the prepared solid precursors at various conditions and their structural and luminescence properties including decay curves were thoroughly studied. In GGAG:Ce, the content of Ga was shown to have strong impact on the lattice parameter and position of the Ce3+ 5 d - $4f$ emission. To induce the formation of Ce4+ ions as defects competing with electron traps, Mg2+ ions were added into the solutions and calcination in air was examined. Both factors were shown to cause the decrease of Ce3+ emission intensity and acceleration of luminescence decay in a similar way. The doping with Sb(III) required calcination of solid precursors in inert atmosphere to prevent formation of an unknown pyrochlore-type phase containing Sb(V). Low temperatures were needed to limit Sb2O3 evaporation during calcination.

The In-doped LiCaAlF6 [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.

International audience; A significant enhancement in the light attenuation length in 22 cm long YAG:Ce and YAG:Ce,Mg fibers grown by the micro-pulling-down method has been reported. This progress has been achieved by the introduction of Al excess into the melt, optimization of thermal conditions of crystallization and post growth annealing. Attenuation length clearly correlates with surface roughness of the fibers. Al excess addition over the stoichiometric composition enhances the fiber surface smoothness. An increase in axial thermal gradient and melt pressure in the crucible capillary die improves the crystallization process stability. Mg codoping provides a Ce3+ scintillation decay time decrease down to 80 ns.

(Gd 0.75 ,Ce 0.015 ,La 0.235 ) 2 Si 2 O 7 (Ce:La-GPS) single crystals co-doped with 0, 100, 200, 500 and 1000 ppm Zr were grown by the Czochralski process, and their scintillation properties were investigated. We investigated the co-doping effect of a stable tetravalent ion in Ce:La-GPS for the first time. The scintillation decay times in the faster component were shortened with increasing the Zr concentration. While the non-co-doped sample showed ∼63 ns day time, the Zr 100, 200, 500 and 1000 ppm co-doped samples showed ∼61, ∼59, ∼57, ∼54 ns, respectively. Additionally, light output, photon nonproportional response (PNR) and other optical properties were investigated.

The ns2-type metal elements (Pb and Sn) doped LiCaAlF6 single crystals were grown by a micro-pulling-down (μ-PD) method. Pb doped LiCaAlF6 [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 SnF2 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.

This paper reports on the preparation and growth of Eu-doped strontium iodide ( ${\rm SrI}_{2}$ ) single crystals by modified micro-pulling-down method. Influence of the ${\rm Eu}^{2 + }$ and ${\rm Eu}^{3 + }$ (introduced in form of ${\rm EuI}_{2}$ and ${\rm EuCl}_{3}$ ) on the luminescence and scintillation properties is analyzed. Sufficient optical quality of prepared single crystals was obtained allowing further characterization of their absorption, radio- and photoluminescence spectra. Photoluminescence and scintillation decay time of grown ${\rm SrI}_{2}$ crystals irradiated under $\gamma $ -ray source were evaluated as well.

Time and cost effective methods are highly desirable in research and development of new scintillators. Modern techniques like micro-pulling down (μ-PD) are suitable for material screening but are unfit for the growth of some crystals. These crystals must be grown by different methods that are usually very time demanding. Modification of halide μ-PD apparatus by custom made elements allowed us to grow cesium hafnium chloride (Cs2HfCl6) by vertical Bridgman method (VB) with significantly reduced growth time. Structural and optical properties of samples prepared from as-grown crystals were studied and compared to crystals grown by standard VB method. The X-ray diffraction confirmed the formation of cesium hafnium chloride single-phase and natural cleavage of the crystals along the (1 1 1) crystallographic plane. Photoluminescence emission, excitation, absorption, and radioluminescence spectroscopy revealed that the optical quality of the crystals grown by modified VB method was comparable to the quality of the crystals grown by standard VB method. Therefore we can use samples prepared by modified VB to estimate and optimize the performance of Cs2HfCl6 based crystals in scintillation detectors. This setup allows the time and cost-effective material screening and it is a powerful tool for the development of new halide based single crystal scintillators.

In this work, a group of Lu 2 SiO 5 :Tb (LSO:Tb) scintillating layers with a Tb concentration between 8% and 19% were investigated by means of synchrotron and laboratory techniques. The scintillation efficiency measurements proved that the highest light yield is obtained for a Tb concentration equal to 15%. At higher concentration, quenching processes occur which lower the light emission. The analysis of the reciprocal space maps of the (082) (280) and (040) Bragg reflections showed that LSO:Tb epilayers are well adapted on YbSO substrates for all the investigated concentrations. The spatial resolution tests demonstrated the possibility to achieve a resolution of 1 μm with a 6 μm thick scintillating layer.

The transparent single crystals of high-melting strontium hafnate (SHO) and strontium zirconate (SZO) have been grown by the floating zone method with vertical mirror arrangement. The X-ray diffraction analysis revealed orthorhombic perovskite structures for both compounds. Evaporation of Sr-containing species during the growth was proved by micro x-ray fluorescence analysis and led to slightly Sr-poor composition in the studied materials. The overall scintillation efficiency of SHO was found to be comparable with that of Bi4Ge3O12 standard scintillator, while that of SZO was considerably lower. The emission spectrum of both compounds was red-shifted when compared to the previously intensively studied powder counterparts and the photoluminescence decay curves became accelerated with pronounced nonexponentiality. The phenomenological model applied to the temperature dependences of the luminescence data revealed that in single crystals the leading luminescence process is either strongly modified with respect to powders or is of a different origin. The scintillation light yield of both materials was determined to be only several tens of photons per MeV under alpha-ray excitation due to strong afterglow, most probably related to ionization of excited state of the luminescence center.

In this paper we report our follow-up research on the Bi 3+ luminescence in orthosilicate compounds, focusing on absorption, luminescent and scintillation properties of YSO:Bi and LSO:Bi SCFs with the Bi concentration ranging from 0.05 to 0.18 at%. For purpose of this research, single crystalline films (SCF) of Y 2 SiO 5 :Bi and Lu 2 SiO 5 :Bi have been grown by the LPE method onto YSO and LSO substrates from the melt-solution based on Bi 2 O 3 flux.

The absorption, luminescence and scintillation characteristics of Y2SiO5:Ce (YSO:Ce) scintillator were investigated and compared to those of Lu1.95Y0.05SiO5:Ce,Ca (LYSO:Ce,Ca) scintillator. Due to the Ca2+ co-doping in LYSO:Ce quantified by GDMS analysis, the Ce4+ center is evidenced in the absorption spectra. For 662 keV γ-rays (137Cs source), YSO:Ce shows a light yield of 15,300 ph/MeV, which is much lower than that of 32,000 ph/MeV obtained for LYSO:Ce,Ca. The coincidence timing resolution for 511 keV annihilation quanta of 234 and 478 ps was obtained, respectively, for LYSO:Ce,Ca and YSO:Ce detectors in coincidence experiment using a BaF2-based detector. Time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.