Fluorescence of Eu3+ ions in TiO2 optical planar waveguides fabricated by the sol-gel method

Abstract

In recent years, rare-earth-doped optical planar waveguides have attracted considerable attention owing to their potential use in the field of integrated optics. To this end, several processes have been employed to produce rare-earth-doped waveguides. Here, we report on the fluorescence of europium trivalent ions in TiO 2 planar waveguides fabricated by using the sol-gel method and the dip-coating procedure. 2-mol % Eu 3+ :TiO 2 films were deposited on optically polished pyrex substrates. These films are 80 nm thick and their refractive index is ranging from 1.8 to 2.1 depending on the anneling temperature (100 o C-600 o C). The fluorescence of Eu 3+ ions was obtained by the excitation in the 5 D 2 level with an Argon ion laser (wavelength=465.8 nm). At room tempurature, the fluorescence spectra were recorded for different annealing temperatures. A correlation was seen between the luminescence spectra and the structural evolution of the gel network. Indeed, it was observed that heat treatment increases the Stark splitting which partially removes the transitions J-degeneracy, indicating that Eu 3+ ions occupy low-symmetry sites and are more embedded in the TiO 2 gel (densification of the TiO 2 gel). Furthermore, it was observed that increasing the annealing temperature entails a high frequency shift and a broadening of the 5 D 0 → 7 F 0 transition, which shows that Eu 3+ ions occupy more distorted sites. These observations are in good agreement with results obtained by waveguide Raman spectroscopy