(source: https://www.rsc.org/periodic-table/element/65/terbium)

Terbium is used in low-energy light bulbs and mercury lamps:

It has been used to improve the sensitivity and hence safety of medical x-rays by allowing reduced exposures: Improvements Relating To X-Ray Sensitive Luminescent Materials (1968).

Terbium salts are used in laser devices: Laser Glass Of Terbium-Containing Quartz Type And Production Thereof (1988).

Terbium-containing materials show magnetostrictive properties and can be used in composites (Magnetostrictive Composites (1999)), position transducers (Fiber optic position transducer with magnetostrictive material and position calibration process (2010)), and actuators (Metallurgical And Mechanical Compensation Of The Temperature Response Of Terbium-Based Rare-Earth Magnetostrictive Alloys (2002)).

References:

All patent information has been obtained from Espacenet (European Patent Office).