O. V. Usovich

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.

Determination of lithium in lithium-ionic conductors by laser-enhanced ionization spectrometry with laser ablation

Laser-enhanced ionisation (LEI) with laser ablation (LA) into a methane–air flame was used for lithium determination in ferrites. Since there is a lack of certified reference materials matrix-matched to ferrites powders, a set of spinel samples were synthesised by means of aerosol spray pyrolysis (ASP) or by annealing the mixture of Li and Fe(III) nitrates. Characterisation by X-ray diffraction showed that the annealed ceramics contained two phases, such as either α-LiFe5O8 and Fe2O3 or α-LiFeO2 and Fe2O3, while ASP ferrites consisted mainly of α-LiFe5O8. Total lithium content in samples was certified by conventional flame photometry after dissolution. We explained the strong matrix effects on the LA-LEI signal by the discrepancy of surface microstructure (and hardness) due to the difference in the conditions of sample preparation. The optoacoustic signal and emission line of Fe I at 382 nm were recorded simultaneously with the LA-LEI signal in order to compensate for matrix effects. We suggest that the microstructure (ceramics or pellets from spherical microparticles) influences both mass removal (proportional to OA signal) and plasma temperature (proportional to AE signal). Correlation plots between OA and AE signals deviated strongly from sample to sample, which was the basis for the application of a multivariate correction procedure to reduce strong matrix effects. 3D correlation plots (LEI vs. OA + AE) for each sample were built to obtain a new analytical signal, which represented the slope of the correlation line to the plane of the OA + AE signals. This normalised signal was free from matrix effects within a concentration range of 0.6–7.5 Li%. The proposed approach allows the use of ferrites synthesised by the various techniques as reference materials in order to build a unified calibration curve.

Luminescence centers in silicate and germanate glasses activated by bismuth

Concentration series of silicate and germanate glasses activated by bismuth are studied. It is shown that luminescence in the IR region is controlled by several active centers related to bismuth. Based on a comparison of spectroscopic characteristics of the studied glasses with the data previously obtained for chloride glass, the observed centers were identified as Bi+, Bi24+, and Bi53+ in germanate glass and Bi+, Bi24+ in silicate glass.

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.

Preparation of SrFe12O19 · 6SrB2O4 magnetic composites by spray pyrolysis

Spray pyrolysis has been used to produce X-ray amorphous precursors with the nominal composition SrFe12O19 · 6SrB2O4 in the form of spherical particles 0.3 to 2 μm in diameter. Heat treatment of the precursors at temperatures from 650 to 900°C has produced platelike strontium hexaferrite particles embedded in a SrB2O4 matrix. With increasing annealing temperature, the average dimensions of the hexaferrite particles increase from 80 × 20 to 450 × 100 nm and the coercivity of the material rises from 240 to 440 kA/m.