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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.

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.

ErF3 doped BaF2 crystals were obtained using the vertical Bridgman technique. Five crystals, with 0.05, 0.08, 0.1, 0.2 and 0.5 mol% ErF3 added to the starting material, have been investigated. The optical absorption spectra reveal the characteristic bands of the Er3+ ions. The distribution of Er3+ ions along the crystals was studied using the optical absorption spectrum of every samples (14–18 slices) cleaved from the as-grown crystals. The Er3+ ions are not uniform distributed along the BaF2 crystals. The segregation coefficient, k, was calculated using the so-called optical absorption method and the Scheil relationship between the dopant concentration and crystal growth conditions. The calculated segregation coefficient of the Er3+ ions ranges from 0.76 to 0.98, for ions with trigonal (C3v) sites, and from 0.6 to 0.86 for clusters, depending on the ErF3 concentration. In the investigated temperature range, only one type of dielectric relaxation has been observed. This relaxation, with activation energy of 0.54 eV is associated with trigonal NNN type (C3v) centers. The charge compensating defects were discussed taking into account both the optical absorption spectra and the calculated number of NNN dipoles whose relaxation were observed.

International audience; We have developed laser grade and highly Yb3+-doped cubic rare-earth sesquioxides (RE2O3, RE = Y, Gd, Lu) single crystals by means of a newly designed high-temperature solution growth method which gives them spectroscopic properties different from those obtained by high-temperature solidification methods. Absorption and emission cross sections, visible anti-Stokes emission, fluorescence decays of the new cubic Gd2O3:Yb3+ single crystals are presented and compared to those of Y2O3:Yb3+ and Lu2O3:Yb3+ crystals. The case of cubic Gd2O3:Yb3+ is particularly interesting since its basic spectroscopic properties have never been detailed and we were capable of achieving Yb-doping level as high as 20%.