1：Experimental Design and Method Selection:

The current Sm-, Tm-, and SmTm-doped TiO2 films were deposited simultaneously onto fused silica and crystalline silicon substrates by ion sputtering a high purity Ti + RE solid target to generate RE concentrations in the low 0.5 at.%. During deposition, the Ti + RE target was bombarded by a beam of Ar+ ions (1.5 keV and 13 mA/cm2) that was generated by a Kaufman cell. The whole procedure was carried out in a high vacuum chamber under an atmosphere of pure oxygen (5x10-4 mbar), by keeping the substrates at 200 0C. Under these conditions, after 120 min, 300 nm thick uniform films were obtained. For comparison reasons, a plain Ti target and the very same deposition conditions were applied to produce a pure TiO2 film. Subsequently, the as-deposited TiO2 films were cut into several 1 cm2 pieces and annealed at increasing temperatures. The treatments were cumulative, 30 min long, and performed at 600, 800, and 1000 0C under a flow of oxygen gas. All films - as-deposited and after thermal annealing - were investigated by X-ray photoelectron spectroscopy XPS (VG Scientific, Al Ka - 1486.6 eV photon excitation, typical resolution ~ 0.85 eV), Raman scattering (Renishaw RM2000, Ar+ laser 488.0 nm photon excitation, spectral resolution of 1 cm-1), optical transmission in the ultraviolet-visible UV-VIS ranges (Ocean Optics HR4000 spectrometer coupled to a DH-2000-BAL light source, typical resolution ~ 2 nm), and photoluminescence PL experiments (Renishaw RM2000 attached to a Linkam THMS 600 temperature stage, Ar+ laser 488.0 nm photon excitation, spectral resolution better than 0.5 nm).