Effect of Ce doping on the magnetic and optical properties of ZnO by the first principle

The absorption spectrum and the magnetic mechanism of Ce-doped ZnO are controversial. To address these issues, we investigated the effects of Ce doping on the magnetic and optical properties of ZnO using geometry optimization and energy calculation based on the first-principle generalized gradient approximation + U (GGA + U) method of density functional theory. First, the undoped ZnO and Ce-mono-doped ZnO supercell models were calculated. Within a limited doping amount in range 3.13-6.25 mol%, higher Ce doping amount results were observed in terms of higher doping system volume, higher formation energy, and lower system stability. Compared with the band gap of pure ZnO, the band gap of each doping system narrowed, and the absorption spectrum showed red-shift. High Ce doping amount led to weak narrowing of the band gap and weak red-shift in the absorption spectrum. The ferromagnetism of the mono-doped systems increased with increasing Ce doping concentration and was mainly attributed to the hybrid coupling effect of the Ce-4f, Ce-5d, and O-2p states. Second, four Zn30Ce2O32 supercell models with the same doping concentration and different spatial arrangements were calculated. A relatively stable antiferromagnetic state was observed when -Ce-O-Ce- was doped along the a-axis bonding of the Ce double-doped ZnO system, whereas favorable ferromagnetic state was found when -Ce-O-Ce- was doped along the deflection of the c-axis. The Curie temperature of doping system can be higher than room temperature.