Effects of vacancies on valence stabilities of europium ions in β-Ca₂SiO₄: Eu phosphors

The formation energies of oxygen and calcium vacancies (VO and VCa) inβ- Ca₂SiO₄ are derived from density functional theory (DFT) calculations performed on constructed supercells, revealing the thermodynamic stabilities of intrinsic defects under Oxygen-poor conditions. On the basis of DFT calculations with HSE06 hybrid functional, defect states produced by vacancies (VO and VCa), dopants Eu (EuCa) and Eu-related defect complexes (EuCa+VO and EuCa+VCa) in the band gap of β- Ca₂SiO₄: host have been further distinguished. The calculated results indicate that the neutral and single negatively charged VCa (i.e., VCa× and VCa′) and the VO in positive charge states may act as trapping centers for electrons. When approaching to Eu²⁺ ions, VCa× and VCa′ may capture the electrons of Eu²⁺ ions and stabilize Eu³⁺ ions at Ca²⁺ sites inβ- Ca₂SiO₄, but not the neutral and positively charged VO. This work demonstrates that electronic structure calculations combined with thermodynamic analyses can be utilized to study the interactions between europium ions and their neighboring defects, and further study the tuning mechanisms of the valence stabilities of europium ions in inorganic compounds. Copyright © 2016 Elsevier Ltd.