Photoluminescence of TiO2 films co-doped with Tb3+/ Gd3+and energy transfer from TiO2/Gd3+ to Tb3+ ions

Nanometer TiO2 thin films doped with different concentration of Tb were prepared by sol–gel method and characterized by X-ray diffraction (XRD), thermogravimetry–differential thermal analysis (TG-DTA), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. XRD results show preferentially oriented (101) anatase films. TEM image indicates that the TiO2 films consist of TiO2 grains with diameter about 15 nm. Under room temperature, strong visible luminescence of Tb3+ ions due to intra-4f shell transitions are obtained and the PL intensity is found to have a well matching relation with the doping concentration of Tb3+ ions. Concentration quenching of PL occurs when Tb3+ concentration exceeds a certain value (9.2 mol%). Furthermore, the luminescence intensity is improved obviously after co-doping with Gd3+ ions because of the sensitization effects of Gd3+ ions to Tb3+ ions in TiO2 system. The energy transfer mechanism from TiO2 and Gd3+ ions to Tb3+ ions was proposed.