A new mixed-anion phosphate Cs2Bi2Sr(P2O7)(PO4)2: Synthesis, characterization, structure and its Eu3+-activated luminescence

A new mixed-anion phosphate crystal Cs 2 Bi 2 Sr(P 2 O 7 )(PO 4 ) 2 was obtained by molten salt method. Single-crystal X-ray diffraction data demonstrated that the compound crystallizes in monoclinic space group P 2 1 /c (No.14) with unit cell parameters a  ​= ​17.708(10) Å, b  ​= ​9.156(5) Å and c  ​= ​9.221(5) Å, β  ​= ​90.160(8) °. The structure exhibits a novel three-dimensional network, which is made up of BiO 6 , BiO 5 , SrO 6 and CsO 11 polyhedra sharing the corners with PO 4 tetrahedra and P 2 O 7 diphosphate groups. The band gap was estimated by the combined density functional theory and experimental study. Photoluminescence property of Cs 2 Bi 2- x Sr(P 2 O 7 )(PO 4 ) 2 : x Eu 3+ showed the excellent thermal stability and high quantum efficiency .