First-Principles Calculation of Absorption spectrum of Co²⁺ in MgAl₂O₄

Abstract

A crystal of MgAl₂O₄ including impurity Co²⁺ is a gemstone known as blue spinel. The origin of the blue color is Co²⁺ ion which substitutes for Mg²⁺ in a 4-coordination site. Since the color and the absorption spectrum have close relation, it is important to analyze the optical absorption of the impurity ion. In this work, in order to reproduce and analyze the absorption spectrum of Co²⁺ in MgAl₂O₄ by first-principles calculation, we calculated the multiplet energies and the oscillator strength of the Co²⁺ ion by using the DVME method based on configuration interaction method.