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International audience; The expensive Ir-consuming growth technology is the main obstacle at widening the area of ortho- and pyrosilicate crystal applications. Possibilities for growing silicate single crystals from melt using Mo or W crucibles in crystallizers with graphite heaters are evaluated. Such feasibility is shown in the examples of Y2SiO5:Ce (YSO:Ce) and La2−xGdxSi2O7:Ce (LaGPS:Ce) scintillation crystals. Application of the edge-defined film-fed growth (EFG) method for silicate growth is limited owing to non-stoichiometry because of the interaction of the CO-containing atmosphere with the melt and crystals. The bulk YSO:Ce and LaGPS:Ce crystals are grown by the Bridgman and Czochralski methods for the first time using much cheaper (compared to Iridium) molybdenum (Mo) or tungsten (W) crucibles. The optical and scintillation parameters of the obtained crystals are determined and compared to the counterparts grown by the conventional Czochralski process in Ir crucibles. The ways for further optimization of technological processes are discussed

International audience; Time-resolved luminescence of YAG-Ce (150 ppm) fiber crystal with Mg co-doping was studied under pulsed X-ray excitation and γ-rays (Cs 662 keV). The initial part of decay kinetics under X-ray excitation is faster than for direct cerium excitation (63 ns). Decay kinetics is also characterized by the presence of slow components with at least two characteristic times longer than Ce3+ radiation time. The slowest one which dominates for t > 500 ns in YAG-Ce without Mg co-doping practically vanishes for samples with 50 ppm co-doping. Decay kinetics under γ-rays are characterized by slower rise time than that under X-rays. These properties can be explained by competition of energy transfer and energy losses in track regions. The distribution of excitations in tracks produced by X-rays differs from that in tracks produced by γ-rays, since the energy of primary electron after γ-quantum conversion is much higher than after X-ray absorption. The stopping power for energetic electrons decreases with increase of electron energy, and therefore the density distribution after X-ray conversion is shifted to higher densities, Therefore, the acceleration of recombination and quenching of excitations is more prominent under X-ray excitation. Specific role of Ce4+ induced by Mg co-doping is also discussed in the paper.

International audience; Time-resolved Z-scan technique gives the opportunity to obtain consistent data for dependence of the yield and decay kinetics from excitation density. The excitation by 4th harmonics of femtosecond Ti:Sapphire laser (6.2 eV) allows to measure with wide dynamical range of excitation density (from 1017 to 1022 excitations per cubic centimeter) CsI luminescence. In the density range 1018-1019 cm−3 the yield of 310 nm band (fast intrinsic luminescence) increases linearly with energy of the laser pulse, and yield of 430 nm band decreases inversely. In the same density range the subnanosecond decay of 310 nm band becomes slower and in microsecond kinetics of 430 nm band increases the contribution of nanosecond components.

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.

International audience; This paper presents the Czochralski growth of SrI2:Eu scintillation crystals. SrI2:Eu is one among the brightest recently discovered scintillators with an excellent energy resolution for spectroscopic identification of radioactive isotopes. The Czochralski crystal growth method is optimal from the point of scaling up of crystal production with minimal investment into upgrade of crystal growth equipment. In this paper, SrI2:Eu crystals with the diameter of up to 50 mm were produced by the developed process based on the Czochralski method. The crystals are prone to cracking, and thermal fields in the crystallizer still should be optimized. Nevertheless, the scintillation parameters of detectors cut from the grown crystals are similar to that in detectors fabricated by the conventional Bridgman-Stockbarger technology. The Eu2+ activator concentration across the crystals is uniform within 5%, as well as the energy resolution, which ranges within 3.6% ± 0.1% at 662 keV. Also, the decay times under X-rays and nonproportionality of scintillation light yield on excitation energy in the range of 31-1274 keV have been determined.

International audience; Scintillation performances of carbon‐doped YAG and YAG:Ce crystals obtained by the Czochralski method under novel conditions of Ar+CO reducing atmosphere is compared to their counterparts obtained by conventional technologies. While light yield and energy resolution in YAG crystals grown under different conditions is similar, a fast luminescence decay component of 4–6 ns is observed in YAG:C grown by the new procedure. Optimization of post‐growth thermal annealing procedure of YAG:Ce,C scintillator provides the very high light yield of 28 200 phot MeV−1, and the energy resolution of 7.8–8.5% at 662 KeV

International audience; Ceramic samples of gadolinium tantalo-niobate mixed crystals were obtained by the solid-state technique. The dependence of luminescence properties on the Nb/Ta ratio in the Gd(NbxTa1-x)O4 system is studied in the 5–450 K temperature range, including thermostimulated luminescence curves in the series of solid solutions. The relation of nonlinear behavior of light output with x variation to non-homogeneous distribution of Nb and Ta in solid solutions is discussed.

International audience; A method of concentration of gas impurities contained in a melt into sealed cavities in a crystal has been proposed for the first time. This makes it possible to determine the amount of gases dissolved in the melt during crystallization by the Edge-defined Film-fed Growth (EGF) technique and the gas pressure in cavities inside the crystals. We also measure the composition of gas inclusions in crystallized melts of Al2O3, Y3Al5O12 and Bi4Ge3O12 and discuss it in connection with crystal growth procedure and quality of crystals.