Difference in the luminescence properties of orthorhombic and monoclinic forms of Y2GeO5:Ln (Ln = Tb3+ and Dy3+)

The luminescence properties of Tb3+ and Dy3+ doped orthorhombic and monoclinic forms of Y2GeO5 are significantly different. Orthorhombic Y2GeO5 doped with Tb3+ and Dy3+ ions gives bright green and blue emission upon UV light excitation with CIE coordinates (0.25, 0.46) and (0.25, 0.24), respectively. The monoclinic Y2GeO5 doped with these ions exhibits light green and yellowish white emissions, respectively. This has been attributed to the differences in crystallographic environments around Y3+ ions in orthorhombic and monoclinic forms of Y2GeO5. Quantum yield of emission for orthorhombic Y2GeO5:Tb (∼29%) is significantly higher than that of the monoclinic Y2GeO5:Tb (∼14%). Lifetime values corresponding to 4F9/2 level of Dy3+ ions in both monoclinic and orthorhombic forms of Y2GeO5 follow an opposite trend with respect to 5D4 level of Tb3+ ions. This is attributed to difference in the concentration quenching mechanism operating for Tb3+ and Dy3+ ions.