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The work presents an experimental study of (Y, Gd)AlO3:Mn2+ crystals grown by the Czochralski method under inert gas atmosphere and by the floating-zone method in the ambient air atmosphere. The Mn2+/Mn4+ ratio, the energy depth of the main dosimetric and shallow traps are analyzed in comparison with the YAlO3:Mn2+ and (Y, Lu)AlO3:Mn2+ crystals studied before. [ABSTRACT FROM AUTHOR]

The X-ray diffraction, Raman scattering, and the temperature dependences of electrical conductivity are investigated for LiNb1 – xTaxO3 nanopowders of different composition (x = 0, 0.25, 0.5, 0.75, 1) obtained by mechanochemical synthesis with the use of the planetary ball mill. All samples were thermally treated at 550 °C; in addition, some of them were annealed at 800 °C. The comparison of the obtained structural parameters of LiNb1 – xTaxO3 samples with the structural data for LiNbO3 and LiTaO3 points to the formation of the LiNb1 – xTaxO3 solid solution. It is revealed that an increase in Ta content in LiNb1 – xTaxO3 nanopowders leads to an increase in the a-parameter of the crystal lattice and a simultaneous decrease in the c-parameter that eventually leads to a slight decrease in the unit cell volume. The average size of crystallites varies from 31 nm for the nanopowders annealed only at 550 °C to 206 nm for the ones additionally annealed at 800 °C. It is shown that although the Raman spectra of the investigated nanopowders are similar, some peculiarities are also observed. They arise from the different compositions of nanopowders, as well as from the presence of LiNb(Ta)3O8, Nb2O5 and/or Ta2O5 parasitic phases. For the first time, an intense band was revealed in the Raman spectra of samples with x ≠ 0. This band is observed in the region of 1008…1009 cm –1 and, probably, cannot be connected with the presence of parasitic phases. The temperature dependences of pressured LiNb1 – xTaxO3 nanopowders conductivity are investigated at temperatures of 400…940 °C. The determined activation energies of the electrical conductivity (1.328 eV for x = 0.5, 1.232 eV for x = 0.75, and 1.166 eV for x = 1) are close to the known values for pure LiNbO3 and LiTaO3 in the temperature range of ionic conduction. [ABSTRACT FROM AUTHOR]

The results of X-ray diffraction studies of the Gd(Mg0.95−x,ZnxMn−0.05)B5O10 down-converting phosphor as a function of Mg–Zn composition are presented. The lattice parameters and unit cell volumes of GdMg0.95−xZnxMn0.05B5O10 pentaborates are examined. The relationships between the structure and optical properties of these materials are explicated based on the results of theoretical calculations of the energy structure. The effect of pressure on the luminescence of Mn2+ in this system was studied up to ca. 32 GPa. The observed quenching of Mn2+ luminescence is due to the crossing of the emitting 4T1g level with the non-emitting 2T2g state. This crossing sets a long-wavelength limit on the possibility of observing the emission of Mn2+ ions, which is around 850 nm. [ABSTRACT FROM AUTHOR]

Detailed investigations of the spectroscopic properties of Cr3+ ions in β-Ga2O3:0.05% Cr3+ single crystals grown by the floating zone technique have been performed in the temperature range 4.5–550 K. The luminescence of Cr3+ ions at low temperatures is due to narrow R-lines (2E → 4A2 transitions) and their vibronic sidebands, whereas the broad intense band (4T2 → 4A2 transition) dominates at temperatures above 200 K. The vibronic sidebands of R-lines with amplitude of less than 5% of the R1-line at a temperature of 4.5 K cover the region of 700–735 nm. The temperature dependences of the luminescence intensity and the decay time of Cr3+ ions indicate the same mechanism of quenching of R-line intensity and shortening of lifetime for 2E of Cr3+ ions. The temperature dependence of the R1-line decay time of β-Ga2O3:Cr3+ with maximal temperature coefficient |Δτ/ΔT| = 0.023 ms K−1 at 120 K and maximal specific sensivitity |(Δτ/ΔT)τ−1| = 0.017 K−1 at 160 K indicates an application potential of this phosphor for low-temperature fluorescence thermometry. [ABSTRACT FROM AUTHOR]

Ytterbium-doped nanocrystalline powders of yttrium aluminum garnet (YAG:Yb3+) with ytterbium content from 5 to 30 at.% have been prepared by the citrate sol–gel method. Phase composition, crystal structure and microstructure of the materials were studied by means of X-ray powder diffraction techniques using both laboratory and synchrotron radiation sources. The photoluminescence spectra and the photoluminescence decay kinetics of Yb3+ ions at room temperature were performed as well. It was revealed that materials calcined at lower (1000 °C) temperature possess a small amount of Yb3+ ions occupying the octahedral sites of Al3+ ions, whereas the materials calcined at 1200 °C form the proper (Y1−xYbx)3Al5O12 solid solution. [ABSTRACT FROM AUTHOR]