Origins of the coloration from structure and valence state of bismuth oxide glasses

We report the origins of the coloration of Bi2O3–SiO2, Bi2O3–B2O3, and Bi2O3–P2O5 glasses. The glasses were quantitatively analyzed to reveal the Bi valence state and network connectivity of silicate, borate, and phosphate. The electronic structure was correlated with Bi valence states, giving two types of signals: those related to optical bandgaps with Bi3+ s–p intra-transition states at 3.6–4.7 eV and visible absorption bands at 2.5–2.7 eV originating from the charge transfer between Bi3+ and Bi5+ and/or plasmonic Bi0 clusters in the colored glasses. These Bi oxide glasses with tvisible transparent and high refractive index are attractive to replace toxic Pb-containing optical glasses.