Elena V. Haula

On the origin of near-IR luminescence in Bi-doped materials (II). Subvalent monocation Bi+ and cluster Bi5(3+) luminescence in AlCl3/ZnCl2/BiCl3 chloride glass

Broadband NIR photoluminescence (from 1000 to 2500 nm) was observed from partially reduced AlCl₃/ZnCl₂/BiCl₃ glass, containing subvalent bismuth species. The luminescence consists of three bands, assigned to Bi⁺ , Bi₂⁴⁺, and Bi₅³⁺ ions. The physical and optical characteristics of these centers and possible contribution to NIR luminescence from bismuth-doped oxide glasses are discussed.

Near infrared photoluminescence of the univalent bismuth impurity center in leucite and pollucite crystal hosts

The bismuth doped aluminosilicate phases leucite (KAlSi2O6), gallium leucite (KGaSi2O6) and pollucite (CsAlSi2O6) display broadband NIR photoluminescence. The active center, responsible for this luminescence, is the Bi+ monocation, which substitutes for the large alkali metal cations. The Al,Si-disorder in the aluminosilicate framework of studied crystal phases results in the heterogeneity of Bi+ luminescent center population, which manifests itself in the characteristic dependency of the luminescence spectrum shape on the excitation wavelength. The relation of NIR emission in Bi+-doped leucite and pollucite phases to the luminescent properties of bismuth-doped glasses is also discussed.

NIR photoluminescence of Bi + impurity center in RbY 2 Cl 7 ternary chloride crystal

Intense long-lived NIR photoluminesce, centered at 920 nm was observed from the single crystalline specimens of RbY2Cl7 ternary chloride, containing Bi+ impurity centers. This crystal phase can be crystallized from the stoichiometric Lewis acidic melt, which promotes the formation of Bi+ ion in sufficient concentration.

New route to Bi + -doped crystals: Preparation and NIR luminescence of K, Rb and Cs ternary chlorides, containing univalent bismuth

In Lewis acidic melts it is possible to obtain the metal cations in unusually low oxidation (subvalent) states with unusual electronic configurations. Specifically, univalent bismuth cation possesses the open shell 6p² configuration with several low-lying electronic exited states, causing the absorption bands in visible/NIR and intense long-lived (hundreds of μs) and broad luminescence in NIR [1-4]. Quantum chemical estimation of Bi⁺ ionic radius in different coordination states gives the values, which place the radius of Bi⁺ very close to Rb⁺ cation. This fact open the possibility to prepare the crystal hosts with alkali cations of similar size (K⁺, Rb⁺, Cs⁺), which can be doped with Bi⁺ by isomorphous substitution. The experimental investigation of NIR luminescence in bismuth-doped RbPb₂Cl₅ [1], KAlCl₄ [2,3], KMgCl₃ [3] and CsI [4] crystals support this conclusion.

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.