First-principles calculation on electronic structure and optical property of BaSi₂O₂N₂:Eu²⁺ phosphor

The crystal structure, electronic structure and optical properties of BaSi₂O₂N₂:Eu²⁺ with varying Eu doping concentrations are computed by the density functional theory (DFT) and compared with experimental results. The results show that the lattice parameters of primitive cells of Ba_1−xSi₂O₂N₂:Eu_x become smaller and Eu–N bond length shortens as Eu concentration increases. The band structure of Ba_1−xSi₂O₂N₂:Eu_x exhibits a direct optical band gap and it's propitious to luminescence. The energy differences from the lowest Eu 5d state to the lowest Eu 4f state decrease with increasing Eu concentrations. The analysis of simulative absorption spectra indicates that the electron transition from Eu 4f states to 5d states of both Eu and Ba atoms contributes to the absorption of Ba_1−xSi₂O₂N₂:Eu_x. Under the coupling effect between Eu and Ba, Ba in BaSi₂O₂N₂ exhibits longer wavelength absorption and increases absorption efficiency. The emission wavelength is deduced by measuring energy differences from the lowest Eu 5d state to the lowest Eu 4f state, and the result is in good agreement with experimental value within experimental Eu²⁺ doping range. - Graphical abstract: The structure and optical property of BaSi₂O₂N₂:Eu²⁺ are computed by DFT and its absorption mechanism is analysed. Results show that absorption peak α is from the host lattice absorption. The absorption peaks β, γ and δ are from Eu 4f to Eu 5d and Ba 6s 5d states. The absorption is attributed to the coupling effect of Eu and Ba atom. - Highlights: • The crystal, electronic structure and optical properties of BaSi₂O₂N₂:Eu²⁺ are computed by DFT. • The lattice parameters of primitive cells reduces and Eu–N bond length shortens as Eu²⁺ increases. • The energy gap from Eu 5d state to Eu 4f state decrease with increasing Eu concentrations. • Both Eu and Ba atoms contributes to the absorption of Ba_1−xSi₂O₂N₂:Eu_x. • The deduced emission wavelength is in good agreement with experimental value.