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 degrees 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. (C) 2017 Elsevier B.V. All rights reserved.