Ultraviolet-blue ionic luminescence of alkali feldspars from bulk and interfaces |
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Authors: | J Garcia-Guinea P D Townsend L Sanchez-Muñoz J M Rojo |
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Institution: | (1) Museo Nacional de Ciencias Naturales, C/Jose Gutierrez Abascal 2, Madrid, E-28006 Spain e-mail: guinea@mncn.csic.es, GN;(2) School of Engineering, Pevensey Building, University of Sussex, Brighton. BN1 9QH, UK, GB;(3) Departamento de Quimica Inorganica, Universitat Jaume I, Borriol, Castellon de la Plana, E-12080 Spain, ES;(4) Instituto Ciencia de Materiales de Madrid, CSIC, Cantoblanco, Madrid, E-28049 Spain, ES |
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Abstract: | Laboratory driven ionic thermal exchange of alkali feldspars from K to Na produces samples which are strongly luminescent
in the ultraviolet region near 320 nm. The sites providing this luminescence are suggested as being correlated with the motion
of Na atoms along interface-interphases of the material (i.e. with Na-O bond fracture). The thermoluminescence peaks show
multi-order kinetics. Thermal preheatings of low albite sensitize the feldspar lattice with respect to thermoluminescence
generated by exposure to UV irradiation and heating produces a strong blue luminescence spread over the range 350 nm to 500 nm
band in feldspars. The upper temperature for thermoluminescence in feldspars is ∼300 °C, which is also the point where ionic
conductivity of albite (010) begins, but the 300 °C region is also the starting point of a large second glow peak in adularia.
Whilst it seems appropriate to link the Na motion to the 350–500 nm emission, it is unclear whether these changes are the
result of the large anisotropic thermal vibration of Na atoms or the massive Na jumps that occur when the lattice reaches
300 °C. A speculative model is considered in which the UV TL emissions of natural minerals are linked to different interface-interphases
(grain boundaries, exsolution limits, twinning planes, antiphase domains). Increased interface coherency energies are related
to the kinetic order and the spectral position of luminescence emission peaks.
Received: 3 December 1998 / Revised, accepted: 17 April 1999 |
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Keywords: | Albite aluminosilicate thermoluminescence self-diffusion ionic-diffusion interfaces ultraviolet emission |
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