The identification of Bi atoms and clusters in Mgsbnd Al silicate glasses

Bi-activated glasses from the MgO-Al₂O₃-SiO₂ system with IR luminescence in the region of 1050-1600 nm have been studied by the high-angle annular dark-field scanning transmission electron microscopy. It was found that individual bismuth ions are present in all samples. Presumably, these ions are Bi³⁺ with low coordination number in the glass network or the subvalent bismuth cations, namely Bi⁺ and Bi²⁺. An increase in the bismuth content, the synthesis temperature together with the change of the synthesis atmosphere from oxidizing (air) to the reducing (nitrogen) leads to the growth of the number of cluster with dimensions in the range of 3 Å to 6 Å. The bismuth dimers are very probable in the samples with a bismuth content close to 0.2 at.%. The clusters with bigger size ( 12 Å) are most likely to be neutral clusters (Bi_n)⁰, which are nuclei for the nano-sized inclusions of the phase of metallic bismuth. In another type of agglomerate with Bi - Bi atoms distances close to 2-4 Å and more correspond the nano-regions enriched in Bi atoms where Bi atoms are embedded in the glass network.