Chalcogen, Rare earth, Transitional, Energy gap for direct transition

• Ba-Cu-F-O-Y
• Co-La-O
• Ba-Cu-O-Y
• Cd-Cs-Se-Y
• Cs-Hg-Se-Y
• rare earth
• transitional
• chalcogen
• non-disordered
• lanthanoid
• orthorhombic
• tetragonal
• trigonal
• cubic
• hexagonal