Sodium nanoparticles in alkali halide minerals: Why is villiaumite red and halite blue?
| Autor: | Laurence Galoisy, Alexis Geisler, Georges Calas |
|---|---|
| Přispěvatelé: | Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Muséum national d'Histoire naturelle (MNHN)-Institut de recherche pour le développement [IRD] : UR206-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS) |
| Rok vydání: | 2021 |
| Předmět: |
Materials science
peralkaline rocks Sodium Inorganic chemistry Halide chemistry.chemical_element Nanoparticle 02 engineering and technology engineering.material 010502 geochemistry & geophysics 01 natural sciences fluorite Geochemistry and Petrology villiaumite 0105 earth and related environmental sciences [PHYS]Physics [physics] halite 021001 nanoscience & nanotechnology Alkali metal UV-visible spectroscopy color Geophysics chemistry radiation damage engineering Halite nanoparticles 0210 nano-technology |
| Zdroj: | American Mineralogist American Mineralogist, Mineralogical Society of America, 2021, 106 (5), pp.838-842. ⟨10.2138/am-2021-7917⟩ The American Mineralogist The American Mineralogist, 2021, 106 (5), pp.838-842. ⟨10.2138/am-2021-7917⟩ |
| ISSN: | 1945-3027 0003-004X |
| DOI: | 10.2138/am-2021-7917 |
| Popis: | The presence of metal Na nanoparticles causes the bright, thermally unstable colors of villiaumite (NaF) and halite (NaCl). These nanoparticles have been suspected for a long time to be caused by external irradiation. Metal nanoparticles, often referred to as metal colloids, cause surface plasmon resonance effects, characterized by a single Lorentzian-shaped absorption band. The color of these minerals is due to metal Na nanoparticles of 2.5–3 nm. A key point is that the resonance wavelength, which corresponds to the maximum of the absorption band, is inversely related to the value of the refractive index of the embedding mineral. This causes the position of the main absorption band to be offset downward by 140 nm in halite relative to villiaumite. As a consequence, the optical transmission window is shifted from the long to the short wavelength domain, explaining the color of blue halite and red villiaumite, respectively. Similar refractive index dependence may explain the purple color of fluorite caused by metallic Ca nanoparticles. Finally, the origin of the villiaumite irradiation may be the presence of Th-rich (about 8.8 wt% ThO2) nano-inclusions, about 500 nm large, illustrating the specific geochemistry of peralkaline rocks where villiaumite is found. |
| Databáze: | OpenAIRE |
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