The BaTiSi3-xGexO9 crystalline phases were synthesized, and their phase-stability and photoluminescent (PL) properties were investigated. The benitoite and tetragermanate-type phases were crystallized in the range of x = 0.75-1.5 and x = 2.0-3.0, respectively. It was suggested that Ge4+ occupies the octahedral Ti site due to the closeness of each ionic radii. The diffuse-reflection spectra revealed an increase in the oxygen-defect center by substitution of Ge in the crystalline phase. Although the BaTiSi2.25Ge0.75O9 phase showed an efficient blue PL at room temperature, the PL intensity decreased drastically with the increasing x, and eventually the BaTiGe3O 9 phase indicated a very weak PL in spite of almost the same structure as benitoite, that is, the absolutely-isolated TiO6 octahedral unit and the Ge3O9 ring. It was suggested that the reduction of the PL intensity in the BaTi (Si, Ge)3O9 phase was caused by the increase in the oxygen-defect center.
- Benitoite phase
- Solid-state reaction