Photoluminescence of samarium-doped TiO2 nanotubes

Samarium (Sm)-modified TiO2 nanotubes (TNTs) were synthesized by low-temperature soft chemical processing. X-ray powder diffraction analyses of the synthesized Sm-doped and non-doped TNTs show a broad peak near 2θ=10°, which is typical of TNTs. The binding energy of Sm 3d5/2 for 10 mol% Sm-doped TNT (1088.3 eV) was chemically shifted from that of Sm2O3 (1087.5 eV), showing that Sm existed in the TiO2 lattice. Sm-doped TNTs clearly exhibited red fluorescence, corresponding to the doped Sm3+ ion in the TNT lattice. The Sm-doped TNT excitation spectrum exhibited a broad curve, which was similar to the UV–vis optical absorption spectrum. Thus, it was considered that the photoluminescence emission of Sm3+-doped TNT with UV-light irradiation was caused by the energy transfer from the TNT matrix via the band-to-band excitation of TiO2 to the Sm3+ ion.