| Summary: | The electronic structures of the luminescent center ions Cr<sup>3+</sup> and Fe<sup>3+</sup> in the deep red phosphors LiAl<sub>5</sub>O<sub>8</sub>:Cr<sup>3+</sup>, α-Al<sub>2</sub>O<sub>3</sub>:Cr<sup>3+</sup>, and γ-LiAlO<sub>2</sub>:Fe<sup>3+</sup> were calculated by the DV-Xα method, in which the local distortion induced by the replacement of Al<sup>3+</sup> sites in the host crystals by the luminescent center ions was reproduced by classical molecular dynamics (MD) simulation. The MD simulations based on classical dynamics allowed for the handling of more than 1000 atoms for the lattice relaxation calculations, which was advantageous to simulate situations in which a small number of foreign atoms (ions) were dispersed in the host lattice as in phosphors, even when typical periodic boundary conditions were applied. The relaxed lattices obtained after MD indicated that the coordination polyhedra around Cr<sup>3+</sup> and Fe<sup>3+</sup> expanded in accordance with the size difference between the luminescent center ions and Al<sup>3+</sup> in the host crystals. The overall profiles of the partial density of states (p-DOSs) of the isolated Cr<sup>3+</sup> and Fe<sup>3+</sup> 3d orbitals were not significantly affected by the lattice relaxation, whereas the widths of the energy splitting of the 3d orbitals were reduced. The electronic structure calculations for Fe–Fe pairs in γ-LiAlO<sub>2</sub> showed that the antiferromagnetic interactions with antiparallel electron spins between the Fe<sup>3+</sup> ions were preferred, especially when the Fe–Fe pair was on the first-nearest neighboring cation sites.
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