The effect of TiO2 on the structure and spectroscopic properties of silica-hafnia based sol-gel waveguides

The effects of titania additions on Er3+ doped silica-hafnia based optical planar waveguides, prepared by sol-gel processing have been studied. Structural changes, including crystallisation induced by the presence of TiO2, were assessed by x-ray diffraction, waveguide Raman spectroscopy and Fourier transform infrared spectroscopy. The Er3+ photoluminescence spectra at ¡­1.5 ¥ìm, the corresponding lifetimes and the Er3+ relative luminescence yields have been determined as a function of the matrix composition, the densification heat treatments and the Er 3+ ion concentration. The Er3+ quenching concentration and its lifetime at the limit of zero rare earth concentration have also been determined. Typical values for the fluorescence lifetimes varied between 6.5-1.5 ms, for Er3+ concentrations ranging from 0.15-2%, in a 75% SiO 2-5% TiO2-20% HfO2 matrix. The presence of TiO2 appears to promote the formation of hafnia-titania mixed crystals. Although the Er3+ quenching concentration was similar for all the systems studied, at ¡­0.6-1.0% Er, even small additions of TiO 2 (¡­5 mol%) were found to increase the Er3+ fluorescence lifetimes of silica-hafnia waveguides by as much as 100%, depending on the actual compositions.