First-principles calculation of the interaction between the oxygen vacancy and the doped Eu²⁺ in chloroborates Ba₂GdB₂ClO₆

First principles calculation is employed to investigate the crystal structure, electronic band structure, sites of the doped Eu2+ and the defect state in Ba2GdB2ClO6 with multi-coordination cation sites. The formation energies of Ba2GdB2ClO6 with Eu2+ substituting have been calculated and the doped Eu2+ prefers to substitute for Gd3+ and Ba2+ sites. The deficiency of O2- ions in the crystal structures will lead to the generation of defect state in the band gap and the deficiency of O2- usually occurred near Eu2+. Through the location of the defect state in the band gap and its composition, the electrons trapped in the defect state would be transferred to Eu2+ through the ways such as low energy light excitation, thermal activation and tunnelling. The defect state in the band structure plays an important role in the charge transfer process. Investigation into the defect state is quite important in the modulation of luminescence materials.