Local Environments of Dilute Activator Ions in the Solid-State

The oxide garnet Y3Al5O12 (YAG), when substituted with a few percent of the activator ion Ce 3+ to replace Y 3+ , is a luminescent material that is nearly ideal for phosphor- converted solid-state white lighting. The local environments of the small number of substituted Ce 3+ ions are known to critically influence the optical properties of the phosphor. Using a combination of powerful experimental methods, the nature of these local environments is determined and is correlated with the macroscopic luminescent properties of Ce-substituted YAG. The rigidity of the garnet structure is established and is shown to play a key role in the high quantum yield and in the resistance toward thermal quenching of luminescence. Local structural probes reveal compression of the Ce 3+ local environments by the rigid YAG structure, which gives rise to the unusually large crystal-field splitting, and hence yellow emission. Effective design rules for finding new phosphor materials inferred from the results establish that efficient phosphors require rigid, highly three- dimensionally connected host structures with simple compositions that manifest a low number of phonon modes, and low activator ion concentrations to avoid quenching.