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

Abstract

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 (Ω₂ and Ω₄ 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.