Iron-Ion Implantation into the Structure of Rock Crystal

Abstract

Iron ions with the energy of 40 keV have been implanted into colorless natural rock crystals to high fluencies of 1.0∙1017 and 1.5∙1017 ion/cm2. These crystals were selected from Svetlinsky deposits of the Southern Urals, which are well-known as minerals with high quality and low content of impurities. A radical change in the color of the crystals after iron-ion implantation and subsequent high-temperature annealing in air has been revealed. The origin of color changes has been studied by using optical methods, as well as Mössbauer and X-ray photoelectron spectroscopy. It has been established that the high-dose and high-energy flow of ions results in the formation of various kinds of structural defects on the surface layer of the matrix, such as electron-hole centers, as well as in the formation at a specific depth of the irradiated matrix of the ultrafine iron-containing phases with a structure, which is non-coherent to the structure of the original matrix. The subsequent high-temperature annealing of the implanted quartz has changed the color of the samples to orange-yellow. This color is similar to the color of natural citrine. The orange color richness of the heat-treated samples grew with increasing amounts of embedded iron impurity in the crystal. The nature of orange-yellow coloration of the implanted and annealed quartz plates can be explained by the formation of ultrafine hematite nanoparticles located in a layer at a depth of ~15 nm. The possibility of refining the color of minerals by ion-beam exposure has been discussed.

Keywords

• quartz
• mountain crystal
• citrine
• ion implantation
• Mössbauer spectroscopy
• ornamental rocks