Used as a dopant in fiber optics to increase the refractive index of the core, enabling efficient light transmission in telecommunications. Also serves as a catalyst in polymerization reactions, particularly in the production of polyethylene terephthalate (PET) for plastic bottles. Employed in infrared optics due to its transparency in the infrared range, making it suitable for lenses and windows in thermal imaging systems. Investigated in semiconductor applications for passivation layers and in some specialized glass formulations to enhance optical properties.