Structural differences in the luminescence properties of lanthanide doped orthorhombic and monoclinic phases of Y2GeO5

Stable monoclinic and metastable orthorhombic phases of Y2GeO5 have been prepared and characterized by XRD and FT-IR. Changes in the local environment around the Y3+ ions in both phases have been probed by Eu3+ doping of the lattices and subsequent measurement of their luminescence properties. The XRD and FT-IR studies revealed that Y2O2 chains exist in the metastable orthorhombic Y2GeO5 phase, while edge-shared distorted YO6 octahedra and YO7 pentagonal bi-pyramids constitute the monoclinic Y2GeO5 lattice. Detailed luminescence studies, including the experimentally evaluated Judd-Ofelt parameters (Omega(2) and Omega(4) values), have confirmed that the polarisability around the Y3+/Eu3+ ions and the associated electric dipole transition probabilities are higher in the metastable orthorhombic Y2GeO5 phase in comparison to the thermodynamically stable monoclinic Y2GeO5. This has been attributed to the lower symmetry of the electronic environment around the Y3+/Eu3+ ions, and the larger Y/Y average separation in the metastable form than that of stable monoclinic Y2GeO5.