Search

The influence of erbium ion concentration on the optical properties of BaF2:ErF3 crystals was investigated. Four ErF3 concentration (0.05, 0.08, 0.15 and 0.5 mol% ErF3)-doped BaF2 crystals were obtained using the Bridgman technique. Room temperature optical absorption in the 250–850 nm spectral range was measured, and the photoluminescence (PL) and decay times were also investigated. The Judd–Ofelt (JO) approximation was used, taking into account four absorption peaks (at 377, 519, 653 and 802 nm). The JO intensity parameters, Ωt (t = 2, 4, 6), were calculated. The influence of the ErF3 concentration on the JO parameters, branching ratio, radiative transition probability and radiative lifetime were studied. The obtained results were compared with measured values and with those reported in the literature. Under excitation at 380 nm, the well-known green (539 nm) and red (668 nm) emissions were obtained. The calculated and experimental radiative lifetimes were in millisecond range for green and red emissions. The intensity of the PL spectra varied with the Er3+ ion concentration. The emission intensity increased linearly or exponentially, depending on the ErF3 concentration. Under excitation at 290 nm, separate to the green and red emissions, a new UV emission band (at 321 nm) was obtained. Other research has not reported the UV emission or the influence of ErF3 concentration on emission behavior.

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.

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; 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.

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%.

International audience; Lead-free piezoelectric materials attract more and more attention owing to the environmental toxicity of lead-containing materials. In this work, we review our first attempts of single crystal grown by the top-seeded solution growth method of BaTiO3 substituted with zirconium and calcium (BCTZ) and (K0.5Na0.5)NbO3 substituted with lithium, tantalum, and antimony (KNLSTN). The growth methodology is optimized in order to reach the best compositions where enhanced properties are expected. Chemical analysis and electrical characterizations are presented for both kinds of crystals. The compositionally-dependent electrical performance is investigated for a better understanding of the relationship between the composition and electrical properties. A cross-over from relaxor to ferroelectric state in BCTZ solid solution is evidenced similar to the one reported in ceramics. In KNLSTN single crystals, we observed a substantial evolution of the orthorhombic-to-tetragonal phase transition under minute composition changes.

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.

Three concentrations of YbF 3 -doped BaF 2 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 the etching method have been used. This method consists in immersing the cleaved sample in 2N HCl at 60°C for 2 minutes. Small etch pits are developed at the emergence points of the dislocations. The etch pits have triangular or hexagonal shapes, depending on the dopant concentration. The dislocations density depends on the dopant concentration.

In this contribution, the authors present, the first laser experiments ever demonstrated with Yb:Gd2O3 and Yb:Y2O3 crystals grown by this new flux method. The demonstrated the first diode-pumped Yb:Gd2O3 laser. Furthermore the new and advantageous flux method allows for the growth of highly Yb-doped sesquioxides which is very promising for the elaboration of cubic Re2O3 dedicated to thin-disk laser applications.

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.

Developing large laser grade cubic rare-earth sesquioxides (RE 2 O 3 , RE=Y,Sc,Lu) single crystals doped with Yb 3+ ions stands as one of the most challenging endeavours of today's crystal growth 1,2 . Recent studies on cubic RE 2 O 3 single crystals have demonstrated their laser potential and highlighted the extreme thermodynamic conditions in which their growth takes place 1-3 . In particular, the laser performances of Lu 2 O 3 :Yb 3+ crystals make them likely to outperform betterknown rivals such as YAG:Yb 3+ or KY(WO 4 ) 2 :Yb 3+ for 976 nm diode-pumped systems 4 . Several mm 3 -sized Yb 3+ -doped Y 2 O 3 , Gd 2 O 3 and Lu 2 O 3 single crystals were recently grown by a newly designed high-temperature solution growth method 5 , and characterized by means of X-ray diffraction, Fourier transformed infrared (FTIR) spectroscopy and electron probe microanalysis (EPMA). Spectroscopic characterizations (absorption and emission cross sections, visible anti-Stokes emission, fluorescence decays) of these new cubic RE 2 O 3 :Yb 3+ (RE=Y,Lu) single crystals are presented.

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.

Various concentrations YbF3 ‐doped CaF2 and Li‐ (Na)‐ codoped crystals were grown using the conventional Bridgman method. The effect of Na+ and Li+ ions on the dielectric spectra was studied. The activation energy and the reciprocal frequency factor have been calculated in order to characterize the observed relaxations. An anomaly of e1 behavior (not reported before) has been observed which is assigned with a phase transition of the order‐disorder type.

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.

YbF3-doped and PbF2-codoped CaF2 crystals were grown using the vertical Bridgman method. The optical absorption spectra reveal the existence of both Yb2+ and Yb3+ ions. The Pb2+ ions modify the characteristic absorption peaks of the Yb2+ ions, but do not influence the Yb3+ ion peaks. The dielectric relaxation gives information about the impurity-defect aggregates. The obtained dielectric spectra show that for our low-YbF3-concentration samples, the main dipole complexes are NN type. The Pb2+ ions do not have an important influence on the dielectric spectra. The activation energy for the dipole reorientation and the relaxation time constant have been determined.

In the present study, various concentrations of ErF3-doped CaF2 crystals were grown using the vertical Bridgman method. The Judd–Ofelt intensity parameters Ω t (t= 2, 4, 6) for f–f transitions of Er3 + ions were determined from optical absorption spectra. The concentration dependence of the intensity parameters radiative transition probability, oscillator strength, branching ratio and radiative lifetime was also investigated. The predicted radiative lifetimes were compared with those of the Er3 + transitions reported in various hosts. Apart from the green and red emissions, reported by other researchers, a UV (314 nm) emission band was observed, not reported previously.