Effect of annealing temperature on spectroscopic features and photocatalytic activity of TiO2:0.07Eu3+ nanoparticles

Abstract

TiO2:0.07Eu3+ thin films were deposited by sol-gel spin coating technique and the effect of annealing temperature on photocatalytic activity (PCA) and red-light emission efficiency was studied. The crystalline structure and phase formation of TiO2:0.07Eu3+ nanophosphors were identified by x-ray diffraction analysis. These results confirm the formation of a single anatase phase for the above films. The HR-TEM images of TiO2:0.07Eu3+ thin film has revealed that all the particles have spherical in shape with an average particle size of 8 nm. From Raman analysis, it is found that the phase formation and modes of vibrations present in TiO2:0.07Eu3+ thin films. The films showed a significant red-shift in band edge with annealing temperatures. The phonon energy was estimated from the PL excitation spectrum and found good agreement with the Raman modes. At 393 nm excitation, the anatase TiO2:0.07Eu3+ nanophosphors exhibited strong PL emission due to f–f transitions of Eu3+ and the dominant red emission was the hypersensitive 5D0 → 7F2 transition. The intensity of luminescence emission was found to increase with an increase in annealing temperatures. Radiative transition rates, fluorescence branching ratio, stimulated emission cross section and radiative decay lifetime was resolved with Judd-Ofelt analysis. The chromaticity coordinate values (0.644, 0.350) were estimated using the CIE-1931 system, which is near to the NTSC red phosphor chromaticity coordinate values. The photo-degradation efficiencies of TiO2:0.07Eu3+ thin films were found to improve with an increase in annealing temperatures. TiO2:0.07Eu3+ film annealed at 550 °C displays high PCA than other films for the degradation of Methylene Blue (MB) under visible light illumination.