Growth Of Lead Iodide (PbI₂) Single Crystals

Lead Iodide (PbI₂) crystal is a promising material for room temperature nuclear radiation detectors, characterized by its wide band gap (E_g=2.32eV), large average atomic number (Z_avg=63) and high density (ρ=6.2g/cm³). Using PbI₂ detector to detect γ -ray or α -ray among1KeV-1MeV, good energy resolution can be observed. But PbI₂ detectors have not been studied in detail because of the lack of high quality PbI₂ single crystals and suitable fabricating technology of the devices.In this paper, the Lead Iodide (PbI₂) poly-crystal has been successfully synthesized directly from high pure element Lead (Pb) and Iodide (I₂) by two-temperature zone vapor-transporting method (TVM). In the synthetic procedure, I₂ vapor was transported from the lower temperature zone to the higher where I₂ combined with Pb into PbI₂. The synthesis reaction was carried in a special quartz ampoule to prevent the ampoule from detonating by controlling the temperature. X-ray diffraction showed that it was high-pure PbI₂ poly-crystal of single-phase and high-density. In crystal growth experiment, PbI₂ single crystal was grown by Vertical Bridgman Method (VBM) in the two- temperature zone vertical growth furnace. The temperature gradient was 15-18℃/cm and the growing speed was 0.6mm/h, on this condition, we obtained PbI₂single crystal with good quality by adopting the position of ampoule in a suitable temperature gradient to prevent iodide atoms escaping from the crystal inside. The obtained PbI₂ crystal with 15mm in diameter and 25mm in length is intact and translucent with yellow appearance, with bandgap of 2.27eV, infrared transmittance of about 40% and resistivity of about 10¹0Ω-cm magnitude. Four X-ray diffraction peaks of the (001) faces have been observed, which showed that the as grown crystal is a perfect single crystal and can be used to fabricate detectors.