Local Environments of Dilute Activator Ions in the
Solid-State Lighting Phosphor Y<sub>3–<i>x</i></sub>Ce<sub><i>x</i></sub>Al<sub>5</sub>O<sub>12</sub>
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Abstract
The oxide garnet Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (YAG),
when substituted with a few percent of the activator ion Ce<sup>3+</sup> to replace Y<sup>3+</sup>, 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<sup>3+</sup> 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<sup>3+</sup> 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