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.

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 spinet 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 alpha-LiFe5O8 and Fe2O3 or alpha-LiFeO2 and Fe2O3, while ASP ferrites consisted mainly of alpha-LiFe3O8. 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.

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.

We observed an intensive near-infrared luminescence in Bi-doped KAlCl4 polycrystalline material. Luminescence dependence on the excitation wavelength and temperature of the sample was studied. Our experimental results allow asserting that the luminescence peaked near 1 um belongs solely to Bi+ ion which isomorphically substitutes potassium in the crystal. It was also demonstrated that Bi+ luminescence features strongly depend on the local ion surroundings.

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.

Monocation Bi+ isomorphically substitutes potassium in KAlCl4 and KMgCl3 chlorides. Having the unique 6p2 open-shell electronic configuration, Bi+ possesses a number of low-lying excited states, and displays broadband long-lived NIR photoluminescence in ternary chloride crystals.

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+, Bi (2) (4+) , and Bi (5) (3+) in germanate glass and Bi+, Bi (2) (4+) in silicate 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.

We have presented a novel method for production of Bi-doped silica glasses based on laser melting of precursor materials. The obtained glasses possessed strong near-infrared broadband photoluminescence between 900 and 1700nm with lifetime about 300μs. The effect of Bi concentration was discussed. According to XPS data, there are two different valence states of Bi ions, which can be related to Bi3+ and Bi in a lower positive oxidation state.

Методом пиролиза аэрозоля получены рентгеноаморфные прекурсоры номинального состава SrFe12O19 · 6SrB2O4 в виде сферических гранул диаметром 0.3–2 мкм. В результате термической обработки прекурсоров при 650–900°С в гранулах формируются пластинчатые кристаллиты гексаферрита стронция, распределенные в матрице SrB2O4. При возрастании температуры отжига средние размеры частиц гексаферрита увеличиваются с 80 нм ? 20 нм до 450 нм ? 100 нм, а коэрцитивная сила материала изменяется от 240 до 440 кА/м.

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.