DEPENDENCE OF LUMINESCENCE OF TITANATES ON THEIR CRYSTAL-STRUCTURE

Compounds A2TiOBO4 (A = Li, Na; B = Si, Ge) show efficient photolumine scence at room temperature. The compound LiTiOPO4 shows luminescence o nly below room temperature. The luminescence of BaTiO3, LiTiO3 and Na2 GeO3 are also reported. From the results it is concluded that titanate octahedra containing a short Ti-O distance show efficient luminescenc e at room temperature if these octahedra are isolated from each other. When the octahedra condense into a framework, the lowest absorption b and shifts to much lower energy, and the Stokes shift and the quenchin g temperature of the emission decreases. This is shown for one-, two-, and three-dimensional frameworks of titanate polyhedra. The effect is ascribed to a broadening of the energy bands.