Eu-doped (Lu/Sc)2O3 thin films grown by thermal evaporation

The sesquioxides Y2O3, Sc2O3 and Lu2O3 are well known hosts for rare-earth-ions, e.g. Eu:Y2O3 as red phosphor or Tm:Sc2O3 as solid state laser. Sesquioxide thin films on α-Al2O3 substrates allow fabrication of crystalline optical coatings, waveguide lasers and photonic structures. We report on the growth of Eu-doped (Lu0.19Sc0.81)2O3 thin films on α-Al2O3 by electron-beam evaporation (EBV). The properties of the films are compared with EBV- and PLD-deposited Y2O3 films. In contrast to EBV-deposited Y2O3 films, the (Lu/Sc)2O3 films are chemically stable. The lattice mismatch with respect to the substrate is −1.5% whereas it is +4.7% for Y2O3. This leads to films textured along the 〈1 1 1〉 direction. The grain size is larger than in EBV-deposited polycrystalline Y2O3 films of similar thickness. The local symmetry of the Eu3+ centers is identical to the symmetry in (Lu/Sc)2O3 bulk crystals. Spectral modifications due to surface effects dominate only when the average film thickness is less than 5 nm. Burying EBV-deposited Y2O3 films below an amorphous Al2O3 cover layer prevents spectral changes and increases the fluorescence quantum yield. The (Lu/Sc)2O3 films resemble PLD-deposited Eu:Y2O3 films in crystal structure as well as in spectroscopic properties and in quantum yield of the fluorescence. Since EBV is a much simpler-and cheaper-technique than PLD, EBV-deposited (Lu/Sc)2O3 films might be favorable for the fabrication of waveguiding and photonic structures for future commercial applications.