Unravel the effect of lattice distortion on the 4f-5d excitation of Ce3+ in garnet phosphors

To increase the red component and improve the color rendering index, the emission redshift of Ce-doped garnet phosphors was extensively studied by a vast amount of researches. But surprisingly, there are still some fuzzy parts in the luminescence mechanism based on the classic configuration coordinate model, which makes some peculiar situations difficult to explain, e.g., the counterintuitive trends of excitation shift in M 2+ -Si 4+ (M 2+ = Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ ) doped Ce: YAG. To figure out the origin of contradiction and reveal the concrete luminescence dynamics, a series of Ce-doped garnet ceramic phosphors were fabricated and characterized in this work. Combined with historical data and current research, it is analyzed that the effects of crystal field splitting and structural rigidity on the luminescent properties of Ce 3+ share the same changing trend with the distortion of cubic symmetry. When the distortion of cubic symmetry is strengthened, the e g splitting and the electron-phonon coupling will be strengthened simultaneously, which leads to the downward and rightward shift of the 5d 1 parabola curve. This effect can well explain the remaining problems in previous researches, and also provides a guideline for future studies on Ce-doped garnet phosphors.