Luminescence of Pb2+ in several calcium borates
The luminescence of Pb2+ in several calcium borates is reported. The different luminescence spectra can be assigned by considering the oxygen coordination. The energy levels of the asymmetrically coordinated Pb2+ ion do not seem to be influenced by the orientation of the BO3 triangles, since the absorption and Stokes shift of the emission band are more or less similar for the differently structured borates. The presence of a ‘free’ oxygen ion shifts the excitation and emission bands to lower energies. The splitting of the excitation bands seems to originate from the influence of the crystal field rather than from the Jahn-Teller effect.