Lanthanide-doped LaSi3N5 based phosphors: Ab initio study of electronic structures, band gaps, and energy level locations

The electronic structures and band gaps of lanthanide (Ln)-doped LaSi3N5 are calculated using the sophisticated screened Coulomb hybrid HSE06-PBE functional. Doping of LaSi3N5 with Ln3+ and Ln2+ dopants results in placing of the Ln 4f bands in the gap between the valence band and the conduction band of the host LaSi3N5. The location of Ln 4f states causes a change in the electronic structures and band gaps and a dramatic change in the luminescence properties of LaSi3N5-based phosphors. The energy level locations are constructed from the ab initio calculated electronic structures and compared with the empirical energy level diagram. The calculated scheme displays all the states which can be used to describe the luminescence process predicted in Ln-doped LaSi3N5. This study can be applied to all compounds doped with lanthanides dopants and provides a tool for materials development.