Terbium(III) oxide is primarily used in phosphors for lighting and display technologies. It emits green light when excited and is a key component in trichromatic fluorescent lamps, enhancing energy efficiency and color rendering. It is also used in cathode ray tubes and plasma displays for high-quality green emission. In solid-state devices, it serves as a dopant in materials for optoelectronic applications. Additionally, it finds use in magneto-optic materials and as a stabilizer in fuel cells due to its ionic conductivity at high temperatures.