Effects of rare-earth concentration and heat-treatment on the structural and luminescence properties of europium-doped zirconia sol–gel planar waveguides

Sol–gel zirconia films doped with Eu3+ concentrations ranging from 0.2% to 10%, were prepared by dip-coating a solution of the starting precursor, zirconium n-propoxide, ethanol, methanol, water, acetic acid and europium nitrate on glass and SiO2/Si wafer substrates. The ZrO2 sol thus synthesized remains stable for several months. Structural characterization of the zirconia films was performed using Waveguide Raman Spectroscopy. These films present an amorphous phase up to an annealing temperature of 400 °C. Above 400 °C the matrix evolves towards a metastable tetragonal phase. This transformation was found to depend on the concentration of Eu3+ ions. Indeed, while for samples doped with 0.2% Eu3+ this transformation occurs around 450 °C, in the case of 10% of Eu3+ ions, the transition is pushed off to 500 °C. The optical losses of these waveguides were found to be about 0.3 dB cm−1 for samples annealed at 400 °C. The surfaces of the films were characterized using Atomic Force Microscopy and the roughness was measured. The Eu-doped films were investigated using Waveguide Photoluminescence Spectroscopy. The dynamical behaviour of the Eu3+ emissions indicated that concentration quenching effect is not observed even when the matrix is doped up to 10%.