Electronic and optical properties of pure and Ce³⁺-doped CaS single crystals: a first-principles prediction

This paper investigates the electronic and optical properties for pure and Ce³⁺-doped CaS crystals by using the first-principles total energy calculations. The results show that CaS:Ce has a direct band gap of 2.16 eV, and the top of the valence band is determined by S 3p states and the bottom of the conduction band is determined by Ce 4f states, respectively. Our results validate that the yellow emission from CaS:Ce is produced by doped cerium and the green emission quenches at 12.5% cerium concentration. The Ce–S bond shows more covalent character than the Ca–S bond.