Blue absorption and red emission of Bi 2+ in solids: strongly spin–orbit coupled 6p levels in low symmetry fields

Wave function embedded cluster ab initio calculations on a (BiO8)(14-) cluster under the effects of a high symmetry Oh confinement potential are used to study the energies of the (2)P1/2, (2)P3/2(1), and (2)P3/2(2) spin-orbit coupling levels of the 6s(2)6p configuration of Bi(2+) in Oh, D4h, D2h, D4, D2d, D2, S4, C4v, C4, C3v, C2v, C2, Cs, and C1 fields, together with the (2)P1/2→(2)P3/2(1) and (2)P1/2→(2)P3/2(2) absorption oscillator strengths and the (2)P3/2(1) radiative lifetime. These levels are responsible for the blue absorptions and the red-orange emissions produced when Bi(2+) is doped in borates, phosphates, sulphates, and other hosts. It is found that the splitting of (2)P3/2 is mainly due to the tetragonal D4h and orthorhombic D2h components of the actual field. It is enhanced by Bi going towards two or four ligands. The intensities of the (2)P1/2→(2)P3/2(1) and (2)P1/2→(2)P3/2(2) absorptions are mostly induced by the Bi displacements and by tetragonal scalenoidal D2d fields. The most favorable fields for a large splitting of the (2)P3/2 level that can drive a red shift of the (2)P3/2(1) →(2)P1/2 emission are the C2v and Cs fields resulting from the combination of D2h orthorhombic fields and Bi approaching two or four ligands on the main orthorhombic planes.