Investigation on modification of ion implanted natural corundum by UV-Vis-NIR spectroscopy

Natural corundum, a crystalline form of aluminium oxide (Al2O3) with impure elements, is an allochromatic mineral whose color varies based on the presence of impurities in the composition. Ion implantation technology can be utilized for enhancing the optical properties of corundum by selecting the implanted ion type leading to modification of the composition and defects. As for the appearance of corundum depending on many factors including brilliance, color, fire (light dispersion), and luster, this research attempted to find out an alternative method for improving the optical appearance and color enhancement of corundum by using ion implantation. Ion beam treatments with 70 keV nitrogen and argon ions and 23 keV oxygen ion at fluence of 1017 ions/cm2 were applied to ruby and sapphire from Thailand, Myanmar, Cambodia, Sri Lanka, Africa, and USA. Additionally, ion beam analysis techniques, i.e., particle-induced X-ray emission (PIXE), together with conventional gemological observations such as optical microscope and UltraViolet-Visible and Near Infrared (UV-Vis-NIR) spectroscopy were applied to understand the phenomena observed. The results revealed the possibility of color changing by ion beams resulting from variation in the ionic stage of trace elements as seen from UV-Vis-NIR absorption spectra. The advantages of ion implantation appear to be new and sustainable for improving corundum properties.