Effect on the stabilization of the anatase phase and luminescent properties of samarium-doped TiO2 nanocrystals prepared by microwave irradiation

Abstract The structural and luminescent properties of TiO 2 and TiO 2 :Sm 3+ powder, synthesized by microwave irradiation using benzyl alcohol as solvent, were studied over an annealing range of 200–1000 °C. Structural and luminescent characterization was carried out by XRD, TEM, HRTEM, HRSEM and PL. Pure synthesized TiO 2 presents similar structural characteristics to other methods and its transformation from the anatase to the rutile phase occurs between 600 and 800 °C. It was determined that the anatase phase of TiO 2 is stabilized when doped with Sm 3+ , even at temperatures up to 1000 °C. Crystal growth of TiO 2 :Sm 3+ powder is very slow, measuring 5 nm at 200 °C and 29 nm at 800 °C. It was observed that the particles consist of nano-sized crystals for all working conditions. Microwave irradiation technic allowed the successful incorporation of Sm 3+ ions into the TiO 2 host lattice, so it is reasonable to conclude that Sm 3+ ions distorted octahedron of TiO 6 to replace Ti 4+ ions. TiO 2 :Sm 3+ nanocrystals show emission of Sm 3+ ion in the visible wavelength region. The visible photoluminescence correspond to transitions from the excited 4G 5/2 level to the 6H 11/2 , 9/2 , 7/2 , 5/2 levels, respectively. The results of spectroscopic measurements of luminescence excitation, imply that Sm 3+ emissions, are due to indirect excitation of the Sm 3+ ions through an energy transference process from electron-hole pairs generated in the TiO 2 host. The increased emission intensity is directly related with high crystallinity obtained by annealing treatment.