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 4G5/2 → 6HJ (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.

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► Sm3+-doped anatase, anatase-rutile, and rutile TiO2 nanoparticles were synthesized by sol-gel.
► A distinct difference in the fine structure of luminescence properties was compared.
► A possible mechanism of photoluminescence of Sm3+-doped TiO2 was proposed.