Effect on the stabilization of the anatase phase and luminescent properties of samarium-doped TiO₂nanocrystals prepared by microwave irradiation

The structural and luminescent properties of TiO₂and TiO₂:Sm³⁺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 TiO₂presents 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 TiO₂is stabilized when doped with Sm³⁺, even at temperatures up to 1000 °C. Crystal growth of TiO₂:Sm³⁺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 Sm³⁺ions into the TiO₂host lattice, so it is reasonable to conclude that Sm³⁺ions distorted octahedron of TiO₆to replace Ti⁴⁺ions. TiO₂:Sm³⁺nanocrystals show emission of Sm³⁺ion in the visible wavelength region. The visible photoluminescence correspond to transitions from the excited 4G_5/2level to the 6H_11/2,_9/2,_7/2,_5/2levels, respectively. The results of spectroscopic measurements of luminescence excitation, imply that Sm³⁺emissions, are due to indirect excitation of the Sm³⁺ions through an energy transference process from electron-hole pairs generated in the TiO₂host. The increased emission intensity is directly related with high crystallinity obtained by annealing treatment.