Bi2+-doped strontium borates for white-light-emitting diodes

We report on Bi2+-doped SrB4O7 and SrB6O10 as orange and red phosphors for white-light-emitting diodes. In both compounds, absorption due to P-2(1/2) -> S-2(1/2) in Bi2+ could be observed and quantified. The emission redshift from SrB4O7 to SrB6O10 and their different phonon satellite spectra are attributed to the enhancement of phonon-electron interaction. Investigation of the reduction mechanism of Bi3+ to Bi2+ suggests that in oxidizing atmosphere, Bi2+ can be stabilized on Sr2+ sites only in such lattices that are dominated by tetrahedrally coordinated boron. (C) 2009 Optical Society of America