  Bismuth-doped luminescent materials have gained significant attention in the
past years owing to their huge potential for the applications in
telecommunications, biomedicine, and displays. However, the controlled
synthesis of these materials, in particular for those luminescing in the
near-infrared (NIR), remains a challenging subject of continuous research
effort. Herein, we show that the low-temperature topotactic reduction by using
Al metal powders as oxygen getters can be adopted as a powerful technique for
the conversion of bismuth-doped red-emitting systems into NIR-emitting cousins
as a result of the creation of unique crystalline networks. Thorough
experimental characterization indicates that the framework oxygen of hosts can
be topotactically extracted, thus producing unique metal-oxygen-metal networks
in the reduced phases while preserving the crystalline structure of the
precursor. We anticipate that this low-temperature topotactic reduction
strategy can be applied to the development of more novel Bi-doped luminescent
materials in various forms that can find a broad range of functional
applications.
