Thin-film structure and fluorescence properties of sol–gel-synthesized Y_2−xEu_xO₃ phosphors

Abstract

Eu-doped yttria (Y_2−xEu_xO₃) thin-film phosphors were prepared using a sol–gel process with post-annealing at 900°C. The Y_2−xEu_xO₃ samples showed cubic bixbyite structure with a gradual increase in the lattice constant (≤0.5%) as x increases (≤0.22). The Eu-doped films exhibited strong photoluminescence (PL) near 2 eV at room temperature with well-resolved fluorescence peaks being ascribed to spin-flip f-f transitions, ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4, 6), within trivalent Eu³⁺(f⁶) ion. Among the six fluorescence lines, the intensity of the strongest 2.03-eV line (J = 2) varies significantly with the Eu content and its optimum value for the maximum PL strength is likely to be near x = 0.1. The Eu-doped films on the Al₂O₃ substrates exhibited significantly higher PL intensities than those on the Si substrates despite no significant difference in structural properties between the two species being observed. It can be understood by comparing the change of complex refractive index for the Y_2−xEu_xO₃/Al₂O₃ and Y_2−xEu_xO₃/Si optical systems.