Perovskite SrSnO (SSO) thin films were epitaxially grown on LaAlO (001) substrates by pulsed laser deposition at various oxygen pressures. X-ray diffraction was carried out to characterize the microstructure of the films, and the results showed that the unit-cell volume of the films increased gradually with lowering the growth oxygen pressures while remaining the perovskite structure. X-ray photoelectron spectroscopy results indicated that oxygen vacancies (OVs) existed in SSO thin films. Optical property measurements showed that all samples have a transmittance of more than 75% in the visible and near-infrared wavelength region. Furthermore, the band gaps of SSO films were found to increase from 4.56 to 5.21 eV with the decrease of deposition oxygen pressures calculated by linear fitting absorption edges of optical transmittance. In order to further ascertain the effect of OVs on band gaps of SSO films, the as-deposited 10 Pa film was annealed at 10 Pa oxygen pressures and the band gap was found to increase by more than 1 eV. Density functional theory was used to explain the effects of OVs on band gaps and the ferromagnetism of SSO films, and the results suggested that an impurity energy level of OVs appeared near the Fermi level, causing the widening of the band gaps, which is consistent with our experimental results. Meanwhile, the room-temperature ferromagnetism was observed in the SSO films, and saturation magnetization increased gradually from 4.46 to 7.69 emu/cm with decreasing the growth oxygen pressures.

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Based on the experimental study of the optical properties of K 2 Ti 6 O 13 doped with Fe or Ag, their electronic structures and optical properties are studied by the first-principles method based on the density functional theory (DFT). The calculated optical properties are consistent with the experiment results. K 2 Ti 6 O 13 doped with substitutional Fe or Ag has isolated impurity bands mainly stemming from the hybridization by the Fe 3d states or Ag 4d states with Ti 3d states and O 2p states and the band gap becomes narrower, the absorption edge of K 2 Ti 6 O 13 thus has a clear red shift and the absorption of visible light can be realized after doping. For Fe-doped K 2 Ti 6 O 13 , the impurity bands are in the middle of the band gap, suggesting that they can be used as a bridge for valence band electrons transition to the conduction band. For Ag-doped K 2 Ti 6 O 13 , the impurity bands form a shallow acceptor above the valence band and can reduce the recombination rate of photoexcited carriers. The experimental and calculated results are significant for the development of K 2 Ti 6 O 13 materials that have absorption under visible light.