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Czochralski growth of mixed cubic sesquioxide crystals in the ternary system Lu2O3-Sc2O3-Y2O3
Cubic rare-earth sesquioxide crystals are strongly demanded host materials for high power lasers, but due to their high melting points investigations on their thermodynamics and the growth of large-size crystals of high optical quality remain a challenge. Detailed thermal investigations of the ternary system Lu2O3-Sc2O3-Y2O3 revealing a large range of compositions with melting temperatures below 2200°C and a minimum of 2053°C for the composition (Sc0.45Y0.55)2O3 are presented. These reduced temperatures enable for the first time the growth of high optical quality mixed sesquioxide crystals with disordered structure by the conventional Czochralski method from iridium crucibles. An (Er0.07Sc0.50Y0.43)2O3 crystal is successfully grown and characterized with respect to its crystallographic properties as well as its composition, thermal conductivity and optical absorption in the 1μm range. © 2021 International Union of Crystallography. All rights reserved.
The electronic structure and the formation of polarons in Mo-doped BiVO4 measured by angle-resolved photoemission spectroscopy
We experimentally investigated the electronic structure of Mo-doped BiVO4 high-quality single-crystals with synchrotron radiation-excited angle-resolved photoelectron spectroscopy (ARPES). By photon-energy dependent ARPES, we measured the bulk-derived valence band dispersion along the direction normal to the (010) cleavage plane, while the dispersion along the in-plane directions is obtained by angle-dependent measurements at fixed photon energy. Our data show that the valence band has a width of about 4.75 eV and is composed of many peaks, the two most intense have energies in good agreement with the theoretically calculated ones. A non-dispersive feature is observed in the fundamental gap, which we attribute to quasiparticle excitations coupling electrons and phonons, i.e. polarons. The determination of the polaron peak binding energy and bulk band gap allows to fix the value of the theoretical mixing parameter necessary in hybrid Hartree–Fock calculations to reproduce the experimental data. The attribution of the in-gap peak to polarons is strengthened by our discussion in the context of experimental transport data and ab initio theory.
Adsorption-controlled growth of La-doped BaSnO3 by molecular-beam epitaxy
Epitaxial La-doped BaSnO3 films were grown in an adsorption-controlled regime by molecular-beam epitaxy, where the excess volatile SnOx desorbs from the film surface. A film grown on a (001) DyScO3 substrate exhibited a mobility of 183 cm2 V-1 s-1 at room temperature and 400 cm2 V-1 s-1 at 10 K despite the high concentration (1.2 × 1011 cm-2) of threading dislocations present. In comparison to other reports, we observe a much lower concentration of (BaO)2 Ruddlesden-Popper crystallographic shear faults. This suggests that in addition to threading dislocations, other defects - possibly (BaO)2 crystallographic shear defects or point defects - significantly reduce the electron mobility.
Spectroscopy and 2.1 µm laser operation of Czochralski-grown Tm3+:YScO3 crystals
We report on growth, temperature-dependent spectroscopy, and laser experiments of Tm3+-doped YScO3 mixed sesquioxide crystals. For the first time, cm3-scale laser quality Tm3+:YScO3 crystals with 2.2 at.% and 3.1 at.% doping levels were grown by the Czochralski method from iridium crucibles. We reveal that the structural disorder in the mixed crystals allows for broad and smooth spectral features even at cryogenic temperatures. We obtained the first continuous wave laser operation in this material at wavelengths around 2100 nm using a laser diode emitting at 780 nm as a pump source. A maximum slope efficiency of 45% was achieved using a Tm3 + (3.1 at.%):YScO3 crystal. Our findings demonstrate the high potential of Tm3+-doped mixed sesquioxides for efficient ultrafast pulse generation in the 2.1 µm range.