Effect of silica coating on the structural and luminescent properties of Sm3+/Yb3+ or Tm3+/Yb3+ co-doped TiO2 nanoparticles

Abstract The luminescent characteristics of spherical titanium dioxide (TiO2) nanoparticles (NP's) doped with Sm3+/Yb3+ and Tm3+/Yb3+ with and without a silica coating were analyzed. These nanoparticles were synthesized using the spray pyrolysis technique and coated with silica through a wet chemical process. The Sm3+/Tm3+ and Yb3+ doping induces a triphasic poly-crystalline structure of rutile and anatase TiO2 and a Sm2Ti2O7/Tm2Ti2O7 cubic phase. A Williamson-Hall analysis was used to monitor the tensions of the NP's crystallites at the various doping concentrations and with addition of the silica shell. The luminescent spectra presented the characteristic emission peaks for the electronic energy levels transitions of the Sm3+/Tm3+ and Yb3+ ions. The Sm3+/Yb3+ co-doped NP's showed a maximum emission peak in the visible region at 612 nm, associated with 4G5/2 → 6H7/2 transitions of the Sm3+ ions. The IR emission peak at 973 nm (2F5/2 → 2F7/2) pertaining to Yb3+. For the combination of Tm3+/Yb3+, two emissions associated with Tm3+ ions were observed at 440 nm (1D2 → 3F4) and 806 nm (3H4 → 3H6). The emission at 973 nm (2F5/2 → 2F7/2) is correlated to the Yb3+ ions. Silica coating of the NP's resulted in luminescence emission intensity increase of about 4 times.