Analysis of Eu-effect on stabilization of the TiO2-anatase structure in high temperature and photoluminescence efficiency for the coatings as-deposited in magnetron sputtering process

In this work the influence of annealing on structural properties and photoluminescence efficiency of TiO2 thin films doped with 0.2 at.% of Eu was described. Coatings were as-deposited in magnetron sputtering process and additionally annealed at 800 °C. Due to application of 'high energy' process the undoped titanium dioxide had fine crystalline rutile structure directly after deposition. In the case of TiO2:Eu film the situation was different. Doping with europium resulted in receiving of nanocrystalline anatase form. Moreover, Eu-dopant was stabilizing the anatase structure in high temperature (at 800 °C) and the phase transformation effect did not occurred. The influence of europium on the microstructure of TiO2 thin films was determined by X-ray diffraction, transmission electron microscope and Raman spectroscopy. The analysis was correlated with photoluminescence measurements. It was found that the crystal form of the TiO2 matrix as well as presence of defect states had a direct impact on PL efficiency. Moreover, the excitation mechanism of photo-generate electrons from TiO2 conduction band via matrix defect states into europium ions was discussed with the respect to location of Eu2+ and Eu3+ ions and its surrounding in the film.