Bismuth valence states and emission centers in Mg-Al-silicate glass

Two Al-Mg-silicate glass sample sets with variable Bi₂O₃ content were prepared. One set was sintered by melting in an iridium crucible at 1850°C in nitrogen, the other—in alumina crucibles at 1550°C in air. Their absorption and emission properties were investigated and compared in the 200–1600 nm spectral range. It was determined that the visible range extinctions values of high-temperature melted samples were almost two orders of magnitude higher than those of the low-temperature melted samples with the same doping level. The concentration dependences of the extinction values at 500, 700 and 800 nm were nonlinear. The investigations allowed us to estimate the absolute concentrations of Bi³⁺ ions and NIR-emitting centers as well as the efficiency of the Bi³⁺ ions conversion into these centers. It was concluded that optical centers emitting at 1100 and 1300 nm contain a pair of bismuth ions. Speculations about some possible structures of Bi dimer NIR-emitting centers were made.