Ab initio calculations of electronic structures of LiYF4 crystals containing F-type color centers

The electronic structures of LiYF4 crystals containing F, F−, and M color centers (F2 center) with the lattice structure optimized are studied within the framework of the density functional theory. The calculation indicated that F, F−, and M color centers have donor energy levels in the forbidden band. The electronic transition energies from the donor level to the bottom of the conduction band are 3.74 eV, 2.85 eV, and 2.42 eV, respectively, which correspond to the 331 nm, 436 nm, and 513 nm absorption bands. It is predicted that the absorption bands observed at 330 nm, 440 nm, and 505 nm could arise from the F, F−, and M centers, respectively, in LiYF4 crystals.