P-6c2

• La-O-Ta
• Ba-O-Si-Ti
• Ba-Se-Sn-Te
• Ba-Eu-O-Si-Zr
• Co-K-O-P
• structural properties
• optical properties
• luminescence
• values of luminescence
• chalcogen
• transitional
• non-disordered
• alkaline
• hexagonal
• trigonal