On the spectra luminescence properties of charoite silicate

J. Garcia-Guinea, P. D. Townsend, N. Can, V. Correcher, L. Sanchez-Munoz, A. A. Finch, D. Hole, M. Avella, J. Jimenez, M. Khanlary

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9 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)403-412
Number of pages10
JournalJournal of Luminescence
Volume128
DOIs
Publication statusPublished - Mar 2008

Keywords

  • charoite
  • cathodoluminescence
  • radioluminescence
  • ionoluminescence
  • thermoluminescence
  • Yakutia
  • STIMULATED LUMINESCENCE
  • ALKALI FELDSPARS
  • CATHODOLUMINESCENCE
  • IONOLUMINESCENCE
  • EMISSIONS
  • QUARTZ

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