Used as a dopant in optical fibers for amplifiers operating in the C-band and L-band of infrared light, particularly in erbium-doped fiber amplifiers (EDFAs) which are essential in long-haul telecommunications. Also employed in upconversion materials for solid-state lasers and infrared detectors. Serves as a precursor in the synthesis of other erbium-containing compounds used in glass coloring and nuclear control applications due to its neutron absorption properties.