Transparent crystalline yttrium aluminum garnet (YAG; Y₃Al₅O₁₂) is a dominant host material used in phosphors, scintillators, and solid state lasers. However, YAG single crystals and transparent ceramics face several technological limitations including complex, time-consuming, and costly synthetic approaches. Here we report facile elaboration of transparent YAG-based ceramics by pressureless nano-crystallization of Y₂O₃–Al₂O₃ bulk glasses. The resulting ceramics present a nanostructuration composed of YAG nanocrystals (77 wt%) separated by small Al₂O₃ crystalline domains (23 wt%). The hardness of these YAG-Al₂O₃ nanoceramics is 10% higher than that of YAG single crystals. When doped by Ce³⁺, the YAG-Al₂O₃ ceramics show a 87.5% quantum efficiency. The combination of these mechanical and optical properties, coupled with their simple, economical, and innovative preparation method, could drive the development of technologically relevant materials with potential applications in wide optical fields such as scintillators, lenses, gem stones, and phosphor converters in high-power white-light LED and laser diode.

Tetrahedral units can transport oxide anions via interstitial or vacancy defects owing to their great deformation and rotation flexibility. Compared with interstitial defects, vacancy-mediated oxide-ion conduction in tetrahedra-based structures is more difficult and occurs rarely. The isolated tetrahedral anion Scheelite structure has showed the advantage of conducting oxygen interstitials but oxygen vacancies can hardly be introduced into Scheelite to promote the oxide ion migration. Here we demonstrate that oxygen vacancies can be stabilized in the BiVO₄ Scheelite structure through Sr²⁺ for Bi³⁺ substitution, leading to corner-sharing V₂O₇ tetrahedral dimers, and migrate via a cooperative mechanism involving V₂O₇-dimer breaking and reforming assisted by synergic rotation and deformation of neighboring VO₄ tetrahedra. This finding reveals the ability of Scheelite structure to transport oxide ion through vacancies or interstitials, emphasizing the possibility to develop oxide-ion conductors with parallel vacancy and interstitial doping strategies within the same tetrahedra-based structure type.