On the spectra luminescence properties of charoite silicate

• Published in: Journal of Luminescence
• Main Authors: Garcia-Guinea, J., Townsend, P. D., Can, N., Correcher, V., Sanchez-Munoz, L., Finch, A. A., Hole, D., Avella, M., Jimenez, J., Khanlary, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2008
• Subjects: charoite; cathodoluminescence; radioluminescence; ionoluminescence; thermoluminescence; Yakutia; STIMULATED LUMINESCENCE; ALKALI FELDSPARS; EMISSIONS; QUARTZ
• Online Access: https://risweb.st-andrews.ac.uk/portal/en/researchoutput/on-the-spectra-luminescence-properties-of-charoite-silicate(6dd92abb-0678-4409-8138-f7385cfd5b9f).html; https://doi.org/10.1016/j.jlumin.2007.09.008; http://www.scopus.com/inward/record.url?scp=36749053443&partnerID=8YFLogxK

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.