Synthesis of orthorhombic and cubic PbF₂ by hydrothermal method

Orthorhombic (α-) and cubic (β-) PbF₂ have been successfully synthesized via a simple hydrothermal process at 200 °C for 8 h using Pb(C₂H₃O)₂ and NH₄F as the raw reaction materials. The crystal structure, morphology, and optical properties of the as-synthesized samples were characterized by X-ray powder diffraction, scanning electron microscopy, and photoluminescence spectroscopy. XRD and SEM results show that the uniform β-PbF₂ microspheres and porous-microspheres with the average diameter about 3 and 5 μm, respectively, were synthesized assisting with citric acid and α-PbF₂ microrods and microtubes with a diameter about 15 and 10 μm, respectively, were synthesized assisting with acetic acid. The reaction conditions influencing the synthesis of these PbF₂ microstructures, such as reaction time, the amount of CTAB, and the molar ratio of F/Pb were investigated. On the basis of a series of observations, phenomenological elucidation of a mechanism for the growth of the β-PbF₂ microspheres and multispheres has been presented. Room-temperature photoluminescence measurements indicated that the as-prepared α-PbF₂ microrods exhibit a strong green emission.