Structure characterization and tuning of perovskite-like NaTaO₃ for applications in photoluminescence and photocatalysis

Perovskite-like NaTaO₃ powders have potential applications in photoluminescence and photocatalysis. Sol-gel, hydrothermal and solid-state methods were used to synthesize NaTaO₃ powders of different crystalline structures, which were identified by Rietveld refinement simulation of X-ray diffraction patterns and transmission electron microscopic diffraction. The refinement results show that the sol-gel specimen has a monoclinic phase with a Ta-O-Ta bond angle of 179° while the hydrothermal and solid-state specimens have an orthorhombic phase with bond angles of 163° and 157°, respectively. By excitation with a 304 nm light source, these NaTaO₃ specimens show photoluminescence emission at ca. 450 nm. The photoluminescence intensity of the specimens had an order solid state >hydrothermal >sol-gel, which is opposite to that of the Ta-O-Ta bond angle. On the other hand, the photocatalytic activity of the NaTaO₃ specimens in water splitting showed the same order as that of the Ta-O-Ta bond angle. This paper directly evidenced that the Ta-O-Ta bond angle affects the separation rate of the photo-induced charges, as well as that structure tuning of tantalates is achievable and crucial for applications in photoluminescence and photocatalysis.