Red shifts of the Eg(1) Raman mode of nanocrystalline TiO2:Er monoliths grown by sol–gel process

Abstract Nanocrystalline monoliths of Er doped TiO 2 were prepared by the sol–gel technique, by controlling the Er-doping levels into the TiO 2 precursor solution. As-prepared and annealed in air samples showed the anatase TiO 2 phase. The average diameter of the nanoparticles ranged from 19 to 2.6 nm as the nominal concentration of Er varies from 0% to 7%, as revealed by EDS analysis in an electron microscope. Photo Acoustic Spectroscopy (PAS) allowed calculate the forbidden band gap, evidencing an absorption edge at around 300 nm, attributed to TiO 2 and evidence of electronic transitions or Er 3+ . The Raman spectra, corresponding to the anatase phase, show the main phonon mode E g(1) band position at 144 cm −1 with a red shift for the annealing samples.