Color tuning of Bi2+ luminescence in barium borates

Mathijs de Jong, A Meijerink

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The luminescence of Bi2+ has its origin in p–p transitions between different spin–orbit states in the 6s26p1 electronic configuration. The divalent state is highly unusual for Bi and because of the low stability of Bi2+, research on the intraconfigurational p–p transitions of Bi2+ is limited. Narrow-band emission has been observed in the orange/red spectral region, which makes Bi2+ luminescence interesting for application in white light LEDs. In this paper we investigate the luminescence of Bi2+ in a variety of borate host lattices with the aim to tune the emission wavelength and to investigate the influence of the host on the luminescence properties. Bi2+ was doped into Sr1−xBaxB4O7, α-BaB2O4, α-BaB4O7, Ba2B10O17 and BaB8O13. Luminescence was observed for Bi2+ in all hosts, except α-BaB2O4, indicating that Bi2+ cannot be stabilized in this host. In the other borates the emission wavelength varies between 586 nm (in BaB8O13) and 671 nm (in α-BaB4O7). The shift in emission wavelength is explained by a variation in crystal field splitting and spin–orbit coupling. The luminescence lifetime of the p–p emission is in the μsμs range, varying between 6 and View the MathML source13μs, reflecting the parity forbidden character of the p–p transition. Narrow-band red emission at 612 nm (FWHM=35 nm) is observed for Ba2B10O17:Bi2+. These luminescence characteristics of Bi2+ are favorable for application in w-LEDs, but an important drawback is that only low concentrations (in the ppm range) can be stabilized in the divalent state.
Original languageEnglish
Pages (from-to)240-247
JournalJournal of Luminescence
Publication statusPublished - 2015


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