Used in fiber optics for high-speed data transmission due to its ability to efficiently transmit infrared light. Key component in infrared optics, including night vision systems and thermal imaging cameras. Employed as a semiconductor material in transistors and diodes, especially in high-frequency applications. Used as a dopant in some types of optical fibers to modify the refractive index. Applied in polymerization catalysts for the production of polyethylene terephthalate (PET). Utilized in solar cells, particularly in multi-junction photovoltaic devices for space and concentrated solar power applications. Found in some types of sensors and detectors for radiation and temperature. Investigated for use in certain biomedical applications, including some experimental cancer therapies and radiopharmaceuticals.