Synthesis and characterization of micro/nano-structured BaHPO4/Ba3(PO4)2/Ba5(PO4)3OH phases and their luminescence

Abstract

Microspheres covered with microcuboids/nanorods and nanoparticles of BaHPO₄/Ba₃(PO₄)₂/Ba₅(PO₄)₃OH phases have been successfully synthesized by a facile hydrothermal (HT) method using the citric acid as a surfactant at different pH values. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and fluorescence spectrometry were used to characterize the samples. It was found that the pH value was a crucial factor for the phase formation and shape determination of the final products, which were discussed in detail. Attractively, the as-prepared BaHPO₄/Ba₃(PO₄)₂/Ba₅(PO₄)₃OH samples emitted an intense blue light in a broad band from 380 to 625 nm, for which the mechanism was complex ions luminescence originating from the transition of ³T₁ → ¹A₁ in PO₄³⁻. Meanwhile, an obvious red shift for the emission band was observed between nano- and bulk-Ba₃(PO₄)₂ synthesized by HT and conventional solid-state (CSS) reactions, respectively, which was due to the effect of the product being nanosized. The same effect was also revealed by the fact that the decay time of the latter was about 2.5 times that of the former. Moreover, the decay mode of Ba₅(PO₄)₃OH was different from those of BaHPO₄ and Ba₃(PO₄)₂, which was ascribed to the effect of the substitution of three OH⁻ for one PO₄³⁻ on their electronic structures.