Used as a precursor in the synthesis of erbium-containing materials for optical applications, particularly in the production of erbium-doped glasses and crystals used in fiber optic amplifiers and lasers. Plays a role in the fabrication of luminescent materials due to erbium’s strong emission in the near-infrared region, useful in telecommunications. Also employed in research for developing phosphors and in some cases as a dopant in solid-state devices. Its hydrate form aids in solubility and processing during material synthesis.