Controllable fabrication of BaF₂ self-assembled 3D Rubik's cube-like architectures emitting blue luminescence

Uniform barium fluoride (BaF₂) micro-crystals with Rubik's cube-like structure have been prepared through a facile and environmentally friendly hydrothermal approach assisted by citric acid as the chelating agent. The crystal structures, morphologies and optical properties of the obtained samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The influential factors on the morphologies and size of BaF₂ particles, including pH values and the molar ratio of Ba²⁺/Cit^3-, were systematically investigated and the possible growth mechanism for BaF₂ three-dimensional (3D) Rubik's cube-like architectures was proposed on the basis of time-dependent experiments. Moreover, the BaF₂ micro-cubes prepared with different amounts of Cit^3- exhibit an intense blue band emission centered at around 423 nm with the excitation of 336 nm ultraviolet (UV) light and the origin of this strong blue light was analyzed in detail. Results provide an effective strategy to fabricate uniform micro-crystals with controllable morphology and excellent optical properties.