Browsing by Author "Hole, D"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Orientation dependence of the ion beam and cathodoluminescence of albite
    Garcia-Guinea, J; Finch, A; Can, N; Hole, D; Townsend, P
    Ion beam induced luminescence and cathodoluminescence of albite produce unexpected differences between (010) and (001) aligned samples. The emission spectra are modified by temperature and different components change in their relative intensity as a result of excitation by different ion beams of H+, H-2(+) and He+. A consideration of processes which can induce the orientation dependence and the role of excitation density that influences the component features are both discussed. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • No Thumbnail Available
    Item
    Ionoluminescence of silicates for ceramic uses at cryogenic temperatures
    Garcia-Guinea, J; Hole, D; Finch, A; Correcher, V; Valle-Fuentes, FJ; Can, N; Townsend, PD
    Requirements on accurate physical properties need new characterization techniques for structural defects. The use of light ions such as H+ and He+ with MeV energies allows penetration to a depth of several microns in most materials producing strong luminescence to gain information on the defect structures present. Examples of ionoluminescence spectra of silicates for ceramic uses are included such as Mn2+-Fe2+ coupled pairs in quartz, Dy3+ in zircon, hatch-twinning in microcline and spontaneous strain and sodium in albite. In cryogenic thermal conditions tectosilicates display both, reorganization of Mn2+ and Fe3+ centres plus a large enlargement of the UV-blue emissions by stress mechanisms. Nesosilicates, i.e., zircon, shows: differences such as existence of REE and (Dy3+) and a selective reduction of some UV-blue peaks, e.g., at 340 and 400 nm..
  • No Thumbnail Available
    Item
    On the spectra luminescence properties of charoite silicate
    Garcia-Guinea, J; Townsend, PD; Can, N; Correcher, V; Sanchez-Muñoz, L; Finch, AA; Hole, D; Avella, M; Jimenez, J; Khanlary, M
    Charoite is a hydrous alkali calcium silicate mineral [K4NaCa7Ba0.75Mn0.2Fe0.05(Si6O15)(2)(Si2O7)Si4O9(OH) center dot 3(H2O)] exhibiting an intense lilac colour related to Mn2+ and Fe3+ colour centres. These ions also contribute to a strong luminescence at similar to 585 and 705 nm. This work studies the thermal dependence of these luminescent centres by (i) thermoluminescence (TL) of pre-heated and pre-irradiated charoite aliquots, (ii) by time-resolved cathodoluminescence (TRS-CL) at room and cryogenic temperatures (RT and CT), (iii) by spatially resolved spectra CL under scanning electron microscopy (SRS-CL-SEM) and (iv) by ion beam spectra luminescence (IBL) with H+, H-2(+) and He-4(+) ions at RT and LT. The main peak, similar to 585 nm, is linked to a transition T-4(1,2)(G)->(6)A(7)(S) in Mn2+ ions in distorted six-fold coordination and the emission at similar to 705 nm with Fe2+ -> Fe3+ oxidation in Si4+ lattice sites. Less intense UV-blue emissions at 340 and 390 nm show multi-order kinetic TL glow curves involving continuous processes of electron trapping and de-trapping along with an irreversible phase transition of charoite by de-hydroxylation and lattice shortening of Delta a = 0.219 angstrom, Delta b = 0.182 angstrom; Delta c = 0.739 angstrom. The Si-O stressed lattice of charoite has non-bridging oxygen or silicon vacancy-hole centres, and Si-O bonding defects which seem to be responsible for the 340 nm emission. Extrinsic defects such as the alkali (or hydrogen)-compensated [AlO4/M+] centres could be linked with the 390 nm emission. Large variations in 585 and 705 nm intensities are strongly temperature dependent, modifying local Fe-O and Mn-O bond distances, short-range-order luminescence centres being very resistant under the action of the heavy ion beam of He-4(+). The SRS-CL demonstrates strong spatial heterogeneity in the luminescence of the charoite. (C) 2007 Elsevier B.V. All rights reserved.