Molten-salt synthesis of luminescent zirconia nanocrystals

Nanocrystals (NCs) of refractory oxides are widely used in both industry and fundamental research, despite their strong covalent bonding posing a serious obstacle to crystallisation under moderate liquid-phase environments. Here, we demonstrate a facile high-liquid-phase synthetic route for the fabrication of a refractory oxide, ZrO2, by employing molten metal chloride salt as the liquid reaction medium. The molten-salt-derived ZrO2 NCs exhibit an average size of approximately 120 nm with a limited size distribution. We also show that the molten-salt process allows for the direct doping of ZrO2 NCs with rare earth (RE) ions using soluble salt precursors, which results in the strong photoluminescence of the products. These luminescent refractory oxides based on RE-doped ZrO2 could be promising candidates for high-temperature sensing applications in industry. Furthermore, the molten-salt process could be generalised for the production of refractory metal oxide NCs that are otherwise not easily produced by ordinary wet-chemistry processes.