Highly Nonstoichiometric YAG Ceramics with Modified Luminescence Properties

Abstract Y ₃ Al ₅ O ₁₂ (YAG) is a widely used phosphor host. Its optical properties are controlled by chemical substitution at its YO ₈ or AlO ₆ /AlO ₄ sublattices, with emission wavelengths defined by rare‐earth and transition‐metal dopants that have been explored extensively. Nonstoichiometric compositions Y _3+x Al _5‐x O ₁₂ ( x ≠ 0) may offer a route to new emission wavelengths by distributing dopants over two or more sublattices simultaneously, producing new local coordination environments for the activator ions. However, YAG typically behaves as a line phase, and such compositions are therefore challenging to synthesize. Here, a series of highly nonstoichiometric Y _3+x Al _5‐x O ₁₂ with 0 ≤ x ≤ 0.40 is reported, corresponding to ≤20% of the AlO ₆ sublattice substituted by Y ³⁺ , synthesized by advanced melt‐quenching techniques. This impacts the up‐conversion luminescence of Yb ³⁺ /Er ³⁺ ‐doped systems, whose yellow‐green emission differs from the red‐orange emission of their stoichiometric counterparts. In contrast, the YAG:Ce ³⁺ system has a different structural response to nonstoichiometry and its down‐conversion emission is only weakly affected. Analogous highly nonstoichiometric systems should be obtainable for a range of garnet materials, demonstrated here by the synthesis of Gd _3.2 Al _4.8 O ₁₂ and Gd _3.2 Ga _4.8 O ₁₂ . This opens pathways to property tuning by control of host stoichiometry, and the prospect of improved performance or new applications for garnet‐type materials.