Thin-film structure and fluorescence properties of sol-gel-synthesized Y2-xEuxO3 phosphors

Abstract

Eu-doped yttria (Y2−xEuxO3) thin-film phosphors were prepared using a sol–gel process with post-annealing at 900°C. The Y2−xEuxO3 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 → 7FJ (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 Y2−xEuxO3/Al2O3 and Y2−xEuxO3/Si optical systems.