Sapphire is a single crystal using aluminum oxide (Al2O3) and the second hardest material found on Earth after diamond. Sapphire is used for a wide variety of applications since it provides a great many properties, such as transparency, physical strength, impact resistance, fretting corrosion, high pressure and temperature durability, and biocompatibility. 

Furthermore, sapphire is considered the ideal material for depositing semiconductor materials for optical and electronic devices. When it is made into a substrate, it can be used for white and blue LEDs or silicon-on-sapphire for RFID purposes. It can be also used in the form of a window or a prism for optical or medical analysis systems.