Characterization of crystalline europium doped α-Y2O3 PLD-films grown on α-Al2O3

In this paper, the epitactical growth of crystalline Eu:Y2O3 films on α-Al2O3 substrates using the pulsed laser deposition (PLD) technique is demonstrated. The spectroscopic characterization shows that the local symmetry of the Eu3+ centers within the films is not changed in comparison to the bulk crystal except those Eu3+ centers that are not located directly at the interface to the substrate. However, at the interface the local symmetry is strongly distorted. Additionally, Eu ions at the interface are responsible for a very strong broad luminescence band centered at E=3 eV which is not observed in bulk Eu3+:Y2O3. We propose that a certain amount of the Eu ions are incorporated as Eu2+ ions at the interface. The Eu2+ (4f5d) states are supposed to be involved in an energy transfer mechanism that results in the 3 eV luminescence. Further, the dopant ions at the distorted interface layer induce traps for excitons, which results in a red shift of the exciton excitation peaks.