Contribution of cations to the photoluminescence properties of Eu-doped barium oxonitridosilicates phosphors

The photoluminescence properties are sensitive to the cations of the host lattice in many phosphors. We selected a typical oxonitridosilicate phosphor (Eu2+-doped Ba3Si6O12N2 green phosphor) to investigate this interesting phenomenon by using Cambridge Sequential Total Energy Package (CASTEP) based on density functional theory (DFT) under generalized gradient approximation (GGA). The effects of partial substitution of Ca atoms for Ba atoms in the Eu2+-doped Ba3Si6O12N2 phosphors were studied. Full geometry relaxation results indicated that both Ca and Eu atoms preferentially occupy the Ba1 sites in the Ba3Si6O12N2 crystal. According to the calculated total and atom resolved partial density of states, the densities of the upper and lower states related to the luminescence properties are mainly offered by Ba and Eu atoms, respectively. The 5d states of Ba atoms provide extra density of states to the upper states, resulting in enhanced luminescence intensity. The substituent Ca atoms dilute the upper states, leading to the degeneration of the luminescence intensity. The calculation results could also be used to explain that Ba atoms are superior than other alkaline atoms in many oxonitridosilicate phosphors.