Optical properties of the Bi+ centre in KAlCl4 crystal

For the first time near infrared (NIR) luminescence of Bi-doped media was observed in 2001 by Fujimoto et al. in silicate glasses. A lot of various Bi-centres that could be responsible for observed NIR luminescence were suggested but there are more and more evidences that it originates from some of low-valence bismuth species like Bi⁺ ions and subvalent Bi clusters (Bi₂⁴⁺, Bi₅³⁺, Bi₈²⁺ etc). Often several luminescent species are observed simultaneously in a Bi-doped media. Nevertheless to date several Bi-luminescent centres (e.g. Bi⁺, Bi₅³⁺ and Bi₈²⁺) was obtained in a “pure” form, i.e. without any additional ones.