Characterisation of the Fe(III):H+ Defect Centre in Natural Amethyst

• Published in: Applied magnetic resonance Vol. 51; no. 11; pp. 1607 - 1619
• Main Authors: Di Benedetto, Francesco, Zoleo, Alfonso, Romanelli, Maurizio
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.11.2020; Springer Nature B.V
• Subjects: Atoms and Molecules in Strong Fields; Continuous radiation; Crystal defects; Crystallography; Dante Gatteschi: On the Occasion of His 75th Birthday; Defects; Electron paramagnetic resonance; Electron spin; Electrons; Laser Matter Interaction; Localization; Magnetic fields; Organic Chemistry; Original Paper; Physical Chemistry; Physics; Physics and Astronomy; Single crystals; Solid State Physics; Spectroscopy/Spectrometry; Spectrum analysis
• ISSN: 0937-9347; 1613-7507
• DOI: 10.1007/s00723-020-01275-1

A natural single crystal of amethyst was investigated by means of continuous-wave and pulsed Electron Paramagnetic Resonance (EPR), with the aim of structurally characterizing the substitutional S2 Fe(III):H + centre. In this centre, Fe(III) replaces Si(IV) in the tetrahedral site, whereas H + is coupled to Fe(III) to maintain the charge balance. The spectroscopic investigations, mainly the interpretation of the Electron Spin Echo Envelope Modulation, allowed a detailed localisation of the proton to be obtained. H + occurs in the channels crossing the crystal parallel to the crystallographic c axis, in a largely eccentric position. The Fe(III)-H + distance, evaluated in 2.70 Å, is found associated with a non-negligible isotropic hyperfine coupling, which can be linked to the relative stability of the S2 centre in natural amethyst.