Ab initio lattice relaxation and electronic structures of LiYF4 crystals containing VF color center

The electronic structures of perfect LiYF4 and the LiYF4 containing lithium vacancy VLi− with the lattice structure optimized are studied within the framework of the density functional theory. By analyzing the lattice relaxation and electronic structure of the LiYF4 containing VLi− we can reasonably believe that once VLi− is formed in LiYF4 crystal, its compensating hole will turn out to be shared by two F− nearest to VLi− forming a diatomic fluoride molecular ion (F2−) perturbed by VLi−, or to say VF color center. According to the molecular-orbital linear combination of atomic orbital (MO-LCAOs) theory, compared to the alkali halides, e.g. LiF, the F2− in VF center in LiYF4 peaks at about 337 nm, which is in agreement with the experimental results.