Effects of framework dopants on luminescent properties of red nitride phosphors via band structure modelling

Currently, researchers have been able to manipulate the luminescent properties and thermal stability of nitride red phosphor Sr₂Si₅N₈:Eu²⁺ through rare earth doping. However, there is limited research on the doping of its framework. This work investigated the crystal structure, band structure, and luminescence properties of Sr₂Si₅N₈: Eu²⁺ and its framework doped systems. We selected B, C, and O as doping elements because the corresponding formation energies of these elements doped structures are relatively low. Then, we calculated the band structures of various doped systems in both the ground and excited states. This analysis aimed to investigate their luminescent properties using the configuration coordinate diagram. The results show that doping with B, C, or O has minimal effect on the emission peak width. The thermal quenching resistance of the B- or C-doped system was enhanced due to the increased energy differences between the 5d energy level of the electron-filled state in the excited state and the bottom of the conduction band, compared to the undoped system. However, the thermal quenching resistance of the O-doped system varies depending on the position of the silicon vacancy. The work indicates that framework doping can also improve the thermal quenching resistance of phosphors besides rare earth ions doping.