Enhance electron-correlation effect on the ruby multiplet energy dependence on pressure

Abstract Development of white light-emitting diode (LED) device is especially important due to the lack of red emissions. As candidates for white LED's novel red phosphors, Mn4+-doped crystals have received growing attention. Hence, the factors that decide the multiplet energies of d3 ions such as Mn4+ and Cr3+ in crystals are very important to understand. Especially Cr3+ activated in α-Al2O3 or the well-known ruby has been widely studied for solid-state laser source. Here we calculated the multiplet energies of ruby under different pressures non-empirically. We also investigated the variables that define the correlation between the local structure and the multiplet energy levels. The results show that the first-principles calculations well reproduced the pressure dependence of 2E transition energy. We found that the behavior of effective Coulomb integral which mainly determines 2E transition energy is consistent from the point of view of delocalization of the 3d orbitals and decrease of the parameters of the Coulomb repulsion.