Optical and Structural Properties of Europium Oxide Thin Films on Silicon Substrates

Abstract

Europium-based materials are known for their intense and stable emission in the visible region. Moreover Eu is stable in both its divalent and trivalent oxidation states. In particular, emission of Eu²⁺ is much stronger, being allowed for electric dipole transition rules and is characterized by a broad peak, centered in the wavelength range 400–600 nm, while that of Eu³⁺ presents several sharp lines at around 600 nm. These peculiar optical properties make Eu‐based systems an interesting material for photonic applications. The optical and structural properties of Eu₂O₃ thin films grown by RF magnetron sputtering on Si substrates have been studied. PL emission has been observed at room temperature and it is strongly dependent on the thermal process. In particular, annealing in O₂ atmosphere leads to an enhancement of the Eu³⁺ emission, while films annealed in N₂ ambient exhibit a very intense PL signal due to Eu²⁺. The chemical and structural characterization of the films, performed by TEM and XPS, reveals that a massive mixing at the Eu₂O₃‐Si interface occurs in N₂‐annealed samples, leading to the formation of Eu (II) silicates, while in the case of O₂-annealed samples we observe the formation of a SiO_x layer at the interface, that minimize the diffusion of Si into the Eu₂O₃ layer.

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