As a wide-bandgap semiconductor material with small dielectric constant and good thermal stability, aluminium nitride (AlN) can theoretically emit light in the deep ultraviolet wavelength region, so it is important in expanding the response of AlN in the visible region. In order to study the influences of La doping on the photoelectric properties of wurtzite AlN crystal, the first-principle plane-wave pseudopotential method and generalized gradient approximation were used to study the lattice constants, electronic structure and optical properties of undoped and La-doped AlN. The calculation results indicate that the intrinsic AlN is a direct-bandgap semiconductor material which both conduction band bottom and valence band top being at the G point, but La-doped AlN forms an indirect-bandgap semiconductor in which the conduction band bottom is at the G point and the valence band top is at the F point. The peak of the density of states is reduced near Fermi energy, and the electronic localization features are significantly diminished. The La doping makes the forbidden band width of AlN narrow, which reduces the photon energy needed for the electron transition, and shows a red shift phenomenon, which expands the influence on visible light. Therefore, this provides a theoretical basis for the study of the photoelectric properties of rare-earth-metal La-doped AlN.

The effect of (La, Ce) doping on the electronic structure and optical properties of Mn4Si7 was studied by using the first-principles calculation method based on density functional theory. The results show that the lattice constant and cell volume of Mn4Si7 increase with rare earth doping, and the structure is more stable after doping. The most stable structure is Ce single doping system. Undoped Mn4Si7 is an indirect band gap semiconductor. Its band gap is 0.786 eV. La doping, Ce doping and La-Ce co-doping all decrease the band gap of Mn4Si7. The band gap is 0.229 eV, 0.247 eV and 0.072 eV, respectively. Undoped Mn4Si7 and La-doped Mn4Si7 are nonmagnetic, Ce-doped and La-Ce co-doped Mn4Si7 are diluted magnetic semiconductor. The static dielectric constant is increased by doping rare earth elements, and the maximum static dielectric constant is La-Ce co-doped system (61.73). The main peak of imaginary part of dielectric function moves to the low energy region in all doping systems and the value of the main peak of the doping system increases. The absorption spectra of the doped system show red shift, and a small new absorption peak appears at the photon energy of 8 eV. In the near infrared band, the absorption coefficient of Mn4Si7 is increased by rare earth doping. The absorption coefficient of La-Ce co-doping system is the largest (1.09 x 10(5) cm(-1)). Rare earth doping enhances the optical absorption performance of Mn4Si7.