Nano-engineered Bismuth-doped silica glasses and origin of near infrared photoluminescence

In present work we investigated the monolithic silica samples prepared from nano-porous silica glasses which were doped with Bismuth triflate, Bi(SO₃CF₃)₃ (BTF), dimeric bismuth(III) complexes with salicylate (HSal) and 2,2´-bipyridyl ligands (Bi₂), and heterobimetallic complexes Bi₂(HSal)₆[Al(acac)₃] (AlBi₂), where Hacac = pentane-2,4-dione, able to accommodate in nano-pores. Our experiments show that in Bi₂-doped silica glasses there exist two types of centres, one of which should be attributed to Bismuth dimers responsible for the NIR PL around of 840 and 1400 nm. These centres provide amplification and laser operation in silica-based fibres in the spectral range of 1350-1450 nm. Another type of optical centres presumably involves aggregates of bismuth ions. These aggregates are responsible not only for NIR PL around 1400 nm and in the spectral range of 500-1200 nm, but also for the strong background absorption which is the main reason of low efficiency of Bi doped fibre lasers. The increase of bismuth concentration in conventional materials results in enhanced aggregation, and, as a consequence, in quenching or marked inhibition of the laser operation.