The luminescence of some oxidic bismuth and lead compounds

Abstract

The luminescence properties of the bismuth compounds Bi2Ge3O9, Bi12MO20 (M = Ge, Ti), and Bi2Al4O9 and of the lead compounds PbGe3O7 and PbM2O4 (M = Al, Ga) are reported and discussed. Bi12MO20 and probably PbGe3O7 show semiconductor-type luminescence. For Bi12MO20 blue and red emission bands are reported which both are ascribed to radiative recombination at (deep) defect centre levels in the band gap. The blue emission originates probably from surface defects. The other compounds show broad emission and excitation bands with large Stokes shifts. The transitions occur on one and the same Bi3+(Pb2+) ion. From decay time measurements it is found that the energy difference between the two lowest excited levels is very small for all compounds. The large Stokes shifts and small trap depths are discussed in terms of the asymmetrical coordination of the 6s2 ions in the compounds under discussion. It is concluded that asymmetrically surrounded Bi3+ ions give rise to luminescence which is characterized by a broad emission band which shows a very large Stokes shift ({reversed tilde equals}2 eV). © 1984.