Energy level diagram

• Er-O-Y-Yb
• Al-Ce-O-Y
• Er-La-O-V-Yb
• Er-O-Y
• Er-O-V-Y-Yb
• chalcogen
• rare earth
• lanthanoid
• luminescent
• transitional
• cubic
• tetragonal
• monoclinic
• orthorhombic
• trigonal