Chalcogen, Non-disordered, Rare earth, Energy gap for direct transition

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