Theoretical assessment of emission efficiency of Eu²⁺-doped phosphors based on alkaline-earth network

This paper presents the methodology for the estimation of the emission efficiency of Eu²⁺-doped phosphors based on their structural information. It was figured out from the electronic structures of CaAlSiN₃:Eu²⁺ and SrSiN₂:Eu²⁺ that the lowest unoccupied molecular orbital (LUMO), which is mainly consisted of Eu 5d orbital, is a key factor to show high efficiency of Eu²⁺ emission. Large contribution of Eu 5d orbital to LUMO is found when there is a strong atomic orbital interaction between alkaline earth atoms and Eu²⁺ atoms. According to the fact, we defined alkaline earth network (ANet) to represent the magnitude of the interaction of alkaline earth atoms with Eu²⁺ atoms in the host crystal. We calculated ANet for 10 Eu²⁺ doped phosphors and correlated them with the experimental values of internal quantum efficiency. ANet has an inversely relationship with internal quantum efficiency. ANet is a good index for qualitatively searching a high efficient Eu²⁺-doped phosphor because it is calculated only from the structural information of targeted phosphors.