This paper investigates the effect of Nb doping on the electronic structure and optical properties of Sr2TiO4 by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory （DFT）.The calculated results reveal that due to the electron doping,the Fermi level shifts into conduction bands（CBs） for Sr2NbxTi1-xO4 with x=0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes,and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region.The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.
The SrTiO3 ： Pr^3＋ material, co-doped with monovalent Li^＋ , divalent Mg^2＋ , and trivalent Al^3＋ was prepared by a new sol-gel method. The phase and crystallinity of the synthesized materials were investigated by powder X-ray diffraction（XRD） and scanning electron microcopy（SEM）. Among the co-doped ion, Al^3＋ incorporation caused the least lattice change and had the best crystallinity. Photoluminescence spectra were taken to investigate the luminescence characteristics. We observed a red luminescence change of SrTiO3 ： Pr^3＋ after being co-doped, and a best enhancement on the red luminescence with the trivalent Al^3＋ was observed. The present results indicated that the charge defect associated with Al^3＋ has led to charge compensation of Pr^＋ and also implied that the charge defects（usually the second dopant ions replacing the A or B sites in the lattice） which are closer to PrSr^＋ contribute more to the red luminescence enhancement.
The effect of In doping on the electronic structure and optical properties of SrTiO3 is investigated by the first-principles calculation of plane wave ultra-soft pseudo-potential based on the density function theory （DFT）. The calculated results reveal that due to the hole doping, the Fermi level shifts into valence bands （VBs） for SrTi1-x InxO3 with x = 0.125 and the system exhibits p-type degenerate semiconductor features. It is suggested according to the density of states （DOS） of SrTi0.875In0.125O3 that the band structure of p-type SrTIO3 can be described by a rigid band model. At the same time, the DOS shifts towards high energies and the optical band gap is broadened. The wide band gap, small transition probability and weak absorption due to the low partial density of states （PDOS） of impurity in the Fermi level result in the optical transparency of the film. The optical transmittance of In doped SrTiO3 is higher than 85% in a visible region, and the transmittance improves greatly. And the cut-off wavelength shifts into a blue-light region with the increase of In doping concentration.
