Used as a dopant in optical fibers and amplifiers, particularly in the development of erbium-doped fiber amplifiers (EDFAs) that are essential for long-distance telecommunications. It serves as a source of erbium ions in solid-state lasers, enabling emission in the infrared range, which is useful in medical and dental laser systems. Also employed in research settings for spectroscopic studies and in the synthesis of other erbium-containing materials for photonic devices. Its paramagnetic properties make it suitable for use in certain magnetic resonance applications and cryogenic experiments.