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

Highlights: • Improved emission colour purity with orthorhombic form of Y₂GeO₅. • Non-stationary quenching exists in orthorhombic and monoclinic forms of Y₂GeO₅:Tb. • Ion pair formation and cross relaxation quenching operating for Y₂GeO₅:Dy samples. - Abstract: 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 ⁴F_9/2 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