Light emission and atomic coordination structure of sol-gel derived erbium-doped SiO₂-TiO₂ thin films

Erbium-doped SiO₂-TiO₂ thin films were prepared by the sol-gel method, using erbium nitrate pentahydrate powder, tetraethyl-orthosilicate (TEOS), and titanium tetraisopropoxide (TTIP) as precursors. The Si/Ti ratios in the SiO₂-TiO₂ films agree with the TEOS/TTIP molar ratio in the sol-gel precursor. Atomic coordination structure of erbium was defined by extended X-ray absorption fine structure spectrometry (EXAFS) and optical properties of the films were characterized by micro-photoluminescence (Micro-PL). The first-neighbor-shell coordination number of erbium in SiO₂-TiO₂ thin films would influence the optical properties. The 700 °C-annealed 80%SiO₂-20%TiO₂:Er1.0% (mol%) film with the lowest coordination number exhibits the highest photoluminescence intensity. Moreover, Fourier transform infrared spectroscopy (FTIR) analysis reveals that the main bonding structures of SiO₂-TiO₂ thin films are related to the erbium dopants. The modification of microstructure and chemical bonding configuration in the SiO₂-TiO₂ films by the Er-doping concentration and its influence on the optical properties are discussed.