The lithium lanthanum tantalate Li5La3Ta2O12 has a cubic garnet structure, denoted LiLaTa-garnet. Blue is octahedral Ta, pink is 8-coordinate La, and green is tetrahedral and octahedral Li.
The use of lithium lanthanum tantalate materials for blue-excitation, red-emitting phosphors for solid-state lighting was explored. These oxide host lattices, Li5La3Ta2O12 and LiTaLa2O6, are well-known solid-state electrolytes for lithium conductivity, yet they have not been investigated for phosphor applications. They potentially offer great flexibility in that the lattice can accommodate substitutions and vacancies. These variations provide opportunity to optimize the luminescence characteristics such as by shifting and broadening adsorption and emission peaks, and increasing the quantum yield, or brightness of emission. For red-emission, Eu-doping, manganese (Mn)-doping, and self-activation were explored.

While Eu-doped LiLaTa phases proved to not be better than previously reported phases, the Mn-doped LiLaTa phases warrant further investigation. In particular, the significant adsorption of blue light via the Mn-doped LiLaTa-perovskite provides a promising material for blue LED down-converters for solid-state lighting. Additionally, this LiLaTa-perovskite phosphor is formed optimally by a unique ion-exchange process not previously reported in the scientific literature. Further work to optimize this material and related materials is planned.

This work was done by May D. Nyman and Lauren E. S. Rohwer of Sandia National Laboratories.

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