Studying the structural and optical properties of Er 3+ doped TiO 2 powders synthesized by the sol-gel process

A series of TiO 2 :xEr powders (with x from 0% to 1% at.) was synthesised by a simple sol–gel process. The structural and optical properties were studied in detail using diffusion reflection spectroscopy, x-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and energy-dispersive x-ray spectroscopy, to systematically determine the band edge, morphology, and structural properties of both undoped and Er-doped TiO 2 samples. Notably, the introduction of Er dopants in the TiO 2 matrix results in a decrease in both the band gap and crystallite size as well as the anatase phase of host matrix TiO 2 remained in the anatase phase even at 800 °C. The heat treatment temperature has an insignificant effect on the green/red emission ratio of Er ions. However, this ratio strongly depends on excitation wavelengths corresponding to down-conversion and up-conversion processes. The colour emission of TiO 2 :Er is easily tunable from green to yellow under different excitations. The emission mechanism of TiO 2 :Er is proposed based on spectroscopy techniques. These findings reveal that the TiO 2 :Er powders are potential materials for labelling and photocatalyst applications.