Large-scale electronic structure calculation on blue phosphor BaMgAl ₁₀O₁₇:Eu²⁺ using tight-binding quantum chemistry method implemented for rare-earth elements

In this study, we carried out large-scale electronic structure calculations on blue phosphor BaMgAl₁₀O₁₇Eu²⁺ (BAM) using an self-consistent charge (SCC) tight-binding quantum chemistry method with an improved convergence for the 4f orbitais of rare-earth elements. Calculation results obtained by the present method are in good agreement with first-principles and experimental results. We first compared the thermodynamic stability and the electronic structures for three different Eu sites. A first-principles calculation showed that the Beevers-Ross site was the most stable site for the Eu atom. Large-scale electronic structure calculations by the improved SCC tight-binding quantum chemistry method suggested that the electronic structures of Eu 5d orbitais are dependent on the shape of Eu 5d orbitais and the positions of oxygen atoms around the Eu atom. We also investigated the effects of an oxygen vacancy (V_o) on the luminescence properties of BAM. We found that energy levels of molecular orbitais (MOs) with main contributions from Eu 5d orbitais were shifted lower by the V_o near the Eu atom, and thus our results suggested that the formation of the V_o near the Eu atom leads to the red shift of the luminescence color.