Luminescence properties of Sm3+-doped TiO2 nanoparticles: Synthesis, characterization, and mechanism

Under different annealing temperature, Samarium-doped anatase monophase, anatase-rutile multiphase, and rutile monophase TiO2 nanoparticles with various doping concentration were synthesized by sol-gel method. The nanoparticles were characterized by means of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectrometer and ultraviolet-visible diffuse reflectance spectroscopy. The results of the photoluminescence excitation spectroscopy measurement imply that the Sm3+ emissions, that originated from the (4)G(5/2) -> H-6(J) (J = 5/2, 7/2, 9/2, and 11/2) intra-4f transitions of Sm3+ ions, are due to the indirect excitation of the Sm3+ ions through an energy transfer process from electron-hole pairs generated in the TiO2 hosts. A distinct difference in the fine structure of luminescence properties between anatase monophase, anatase-rutile multiphase, and rutile monophase TiO2 nanoparticles were compared. Combined with the theoretical calculations results, a possible mechanism of photoluminescence of Sm3+-doped TiO2 was proposed. (C) 2012 Elsevier B. V. All rights reserved.