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International audience; Lithium molybdate Li2MoO4 (LMO) crystals of mass ranging between 350 and 500 g are excellent candidates to build heat-scintillation cryogenic bolometers likely to be used for the detection of rare events in astroparticle physics. In this work, numerical modeling is applied in order to investigate the Czochralski growth of Li2MoO4 crystals in an inductive furnace. The numerical model was validated by comparing the numerical predictions of the crystal-melt interface shape to experimental visualization of the growth interface. Modeling was performed for two different Czochralski furnaces that use inductive heating. The simulation of the first furnace, which was used to grow Li2MoO4 crystals of 3–4 cm in diameter, reveals non-optimal heat transfer conditions for obtaining good quality crystals. The second furnace, which will be used to grow crystals of 5 cm in diameter, was numerically optimized in order to reduce the temperature gradients in the crystal and to avoid fast crystallization of the bath at the later stages of the growth process.

A new R&D on lithium molybdate scintillators has begun within a project CLYMENE (Czochralski growth of Li 2 MoO 4 crYstals for the scintillating boloMeters used in the rare EveNts sEarches). One of the main goals of the CLYMENE is a realization of a Li 2 MoO 4 crystal growth line to be complementary to the one recently developed by LUMINEU in view of a mass production capacity for CUPID, a next-generation tonne-scale bolometric experiment to search for neutrinoless double-beta decay. In the present paper we report the investigation of performance and radiopurity of 158-g and 13.5-g scintillating bolometers based on a first large-mass (230 g) Li 2 MoO 4 crystal scintillator developed within the CLYMENE project. In particular, a good energy resolution (2–7 keV FWHM in the energy range of 0.2–5 MeV), one of the highest light yield (0.97 keV/MeV) amongst Li 2 MoO 4 scintillating bolometers, an efficient alpha particles discrimination (10 σ ) and potentially low internal radioactive contamination (below 0.2–0.3 mBq/kg of U/Th, but 1.4 mBq/kg of 210Po) demonstrate prospects of the CLYMENE in the development of high quality and radiopure Li 2 MoO 4 scintillators for CUPID.

In the last decades, fluorites crystals (MeF2, Me = Ca, Ba, Sr, Pb) doped with trivalent rare-earth ions (RE3+) have attracted attention of research community due to their various applications such as: lasers, quantum electronics, scintilators or photosensors in PET (positron-emission-tomography) scanner. The goal of this work is to investigate the spectoscopic properties of gamma irradiated BaF2:CeF3 crystal. In order to investigate the quality of the as-grown crystal the dislocation density was estimated. The dislocation density is around 1.3×105 disloc./cm2. After irradiation with gamma rays, the absorption spectra reveal the appearance of a new absorption band in the 400-600nm region. The induced absorption bands depend on the gamma rays dose and the peaks intensities increase with the dose of radiation.In the last decades, fluorites crystals (MeF2, Me = Ca, Ba, Sr, Pb) doped with trivalent rare-earth ions (RE3+) have attracted attention of research community due to their various applications such as: lasers, quantum electronics, scintilators or photosensors in PET (positron-emission-tomography) scanner. The goal of this work is to investigate the spectoscopic properties of gamma irradiated BaF2:CeF3 crystal. In order to investigate the quality of the as-grown crystal the dislocation density was estimated. The dislocation density is around 1.3×105 disloc./cm2. After irradiation with gamma rays, the absorption spectra reveal the appearance of a new absorption band in the 400-600nm region. The induced absorption bands depend on the gamma rays dose and the peaks intensities increase with the dose of radiation.

The spectroscopic properties of the gamma irradiated BaF2:Er3+ crystals were studied. BaF2:0.2 mol% ErF3 crystal was grown using the vertical Bridgman method. The Judd-Ofelt intensity parameters, Ωt (t = 2,4,6) for f-f transitions of Er3+ ions were determined from optical absorption spectra recorded before and after gamma irradiation at various doses. The influence of gamma irradiation dose on the Judd-Ofelt parameters and on the radiative transition probability, on the branching ration and on the radiative lifetime was also investigated. The predicted radiative lifetimes were compared with those measured and with those reported by other authors. Apart from the green and red emissions, arising under excitation at 378 nm, a new UV emission band around 321 nm was observed under excitation at 290 nm. This emission was not reported before. Using the Fuchtbauer-Ladenburg method, the emission cross section and optical gain parameter of the red and green emission band were calculated.

International audience; Polycrystals and centimeter-sized BaTiO3-based single crystals were grown by top seeded solution growth from the BaTiO3–CaTiO3–BaZrO3 system. High effective partition coefficients of Zr ranging from 15 to 6 with small Zr content have been calculated from Castaing microprobe measurements, whereas those of Ca increase slightly from 0.45 to 0.7. A spinodal decomposition mechanism is emphasized during the growth leading to the emergence of two phases with close compositions. Chemical analysis displayed periodical Zr and Ca content fluctuations within the whole boules, and Rietveld measurements highlighted two phases belonging to perovskite structures with tetragonal P4mm and orthorhombic Amm2 space groups. Samples with various calcium and zirconium contents were characterized by means of dielectric and piezoelectric measurements. Most efficient samples are indistinctly polycrystals or oriented single crystals where electromechanical performances are compositional-dependent. Polycrystalline samples and single crystals oriented along (001)pc and (110)pc displayed Curie temperatures ranging from 50 to 111 °C. Electromechanical coupling factor up to 58% and piezoelectric charge coefficient d33 = 496 pC·N–1 were obtained at room temperature. The miscibility gap between the two perovskite solid solutions as well as Ca and Zr element content variation in single crystals lower crystal piezoelectric response that remains nonetheless of the same efficiency compared to that of ceramics of the same composition.

Various concentrations of YbF3 –doped and NaF or PbF2 co-doped CaF2 crystals were grown using the conventional Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum using a shaped graphite furnace. The crystals have been cooled to room temperature using an established procedure. Room temperature absorption spectra have been obtained using a Shimadzu 1650PC spectrophotometer. Photoluminescent properties in IR spectral range were analyzed using a spectrofluorimeter Horiba Fluorolog 3. An IR laser diode at 932 nm was also used an directly injected in the equipment. The emission spectra are influenced by the concentration of co-dopant added to the melt, and the excitation wavelength. The high emission peak at 979 nm overlaps with the absorption peak. The highest intensity in the IR emission (around 1029 nm) is obtained for CaF2:0.72 mol% YbF3 crystal by excitation at 932 nm (diode lamp).

BaF2:0.17 mol%YbF3 crystal was grown using the conventional Bridgman technique. The optical absorption spectra reveal the existence of both Yb2+ and Yb3+ ions with the characteristic bands of the trivalent ions in the near-IR region and of the divalent ions in the UV spectral domain. The concentration distribution of the Yb2+ and Yb3+ ions among the sample was investigated using the optical absorption method. The segregation coefficient of the two types of Yb ions has been determined. From our calculations the segregation coefficient of the Yb3+ ions in BaF2 host is ≈ 0.7, and of the Yb2+ ions is ≈ 0.6.

Yb:Gd2O3 appears as a new crystal laser since it cannot be grown in its cubic-phase by classical growth methods. We present laser demonstration with Yb:Gd2O3 and Yb:Y2O3 grown by the flux method using new solvent.

International audience; We present, to the best of our knowledge, the first laser demonstration of an Yb-doped Gd2O3 cubic crystal. This crystal was obtained by the flux method using an original borate-based solvent, which was particularly well suited to the growth of rare earth sesquioxide crystals at half the working temperature of classical growth techniques. This flux method is a very interesting alternative for the production of laser sesquioxide crystals, not only because it provides access to new matrices of the cubic polymorph, but also because it permits high Yb3+-doping levels for these crystals. The first laser results of two highly Yb3+-doped sesquioxides, namely Gd2O3 and Y2O3, grown by this flux method are presented here, including the Ti:sapphire and diode pumping configurations. Laser efficiencies and emission spectra for these two crystals were studied and compared.

Various concentrations YbF3 -doped CaF2 and Pb2+ - codoped crystals were grown using the conventional Bridgman method. Transparent colorless crystals were obtained in graphite crucible in vacuum (∼ 10−1 Pa) using a shaped graphite furnace. The crystals have been cooled to room temperature using an established procedure. In order to study the etch pits morphology and the dislocations density we used the chemical etching method. This method consists in immersing the cleaved sample in 4NHCl at 60°C for 5 minutes. Small pits are developed at the emergence points of the dislocations. The etch pits have hexagonal shapes for pure CaF2 crystal and triangular sahpes for doped crystals. The dislocations density depends also on the dopant or on the codopant concentration.

The CaF2:0.83 mol% ErF3 crystal was grown using the vertical Bridgman method. The Judd‐Ofelt intensity parameters Ω2, Ω4, and Ω6 for f−f transitions of Er3+ ions were determined from the optical absorption spectrum. The predicted radiative lifetimes are compared to those of Er3+ transitions reported in various hosts. Apart from the green and red emission, reported by other researchers, an UV (314 nm) emission band was observed, not reported before.

The double‐doped CaF2:(0.14 mol% ErF3,1.31 mol% YbF3) and CaF2:0.12 mol% ErF3 crystals were grown in our crystal research laboratory using the vertical Bridgman method. The Judd‐Ofelt intensity parameters Ω2, Ω4, and Ω6 for f−f transitions of Er3+ ions were determined from the optical absorption spectra using various groups of transitions. Using the J‐O parameters the radiative transition probability, oscillator strength, branching ratio and radiative lifetime of Er3+ transitions have been calculated. The radiative transition probability and radiative lifetimes are compared to those of Er3+ transitions in other hosts.

Judd–Ofelt (J–O) analysis is used to estimate the magnitude of the forced (4f–4f) transition probabilities of Er3+ ions in double-doped (Er,Yb) : CaF2 crystals. The studied crystals were grown in our crystal research laboratory using the vertical Bridgman method. The J–O intensity parameters Ω2, Ω4 and Ω6 were calculated from the optical absorption spectra. These parameters were then used to evaluate the spontaneous transition probability, the line strength, the branching ratio and the radiative lifetime. The obtained radiative decay rates were compared with the luminescence spectra.