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 degrees while the hydrothermal and solid-state specimens have an orthorhombic phase with bond angles of 163 degrees and 157 degrees, 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.