Highly non-stoichiometric YAG ceramics with modified luminescence properties

Yttrium aluminium garnet Y3Al5O12 (YAG) is a widely used phosphor host. Its optical properties are tuned by chemical substitution at its YO8 or AlO6/AlO4 sublattices, with emission wavelengths defined by a finite number of rare-earth (YO8 sublattice) and transition-metal (AlO6/AlO4 sublattice) dopants which have been explored extensively. Non-stoichiometric compositions Y3+xAl5-xO12 (x ≠ 0) may offer a route to new emission wavelengths by distributing dopants over multiple crystallographic sites, but deviation from Y3Al5O12 stoichiometry is difficult to achieve and limited generally to < 1% excess Y3+. Here we report a series of highly non-stoichiometric YAG ceramics Y3+xAl5-xO12 (0 ≤ x ≤ 0.4), with up to 20% of the AlO6 sublattice substituted by Y3+, synthesised by advanced melt-quenching techniques. This impacts the up-conversion luminescence of Yb3+/Er3+-doped systems, whose yellow-green emission contrasts with the red-orange emission of their stoichiometric counterparts. This contrasts with YAG:Ce3+ where the dopant ions occupy the YO8 sublattice exclusively, with down-conversion luminescence that is hardly affected by host nonstoichiometry. Beyond YAG, analogous highly non-stoichiometric systems should be obtainable for a range of functional garnets, demonstrated here by the successful synthesis of Gd3.2Al4.8O12 and Gd3.2Ga4.8O12. This opens the way to property tuning by control of garnet host stoichiometry, and the prospect of improved performance or new applications for garnet-type optical and magnetic materials.