Local structure around Er3+ in SiO2-HfO2 glassy waveguides using EXAFS

Er3+-doped SiO2-HfO2 glassy waveguides with HfO2 concentrations ranging from 10 to 50 mol % were prepared using the sol-gel route and deposited on v-SiO2 substrates using the dip-coating technique. The local environment around Er3+ ions was determined from Er L-3-edge extended x-ray-absorption fine-structure (EXAFS) measurements. The first coordination shell around Er3+ ions is composed of oxygen atoms. Hafnium is the main constituent of the second coordination shell of Er3+, differing from the cases of pure SiO2 and SiO2-TiO2 glassy hosts, in which silicon is the main atomic species. The local structure around Er3+ ions has been found to be independent on HfO2 concentration within the studied composition range. This fact implies that Er3+ ions are preferentially dispersed in HfO2-rich regions of the glassy waveguide, even at the lowest HfO2 concentration. For all samples, no Er3+-Er3+ coordination shell has been detected by EXAFS. The presented structural results allow us to understand some spectroscopic properties typical of Er3+-doped SiO2 glassy waveguides co-doped with HfO2.