Growth Of Lead Iodide Single Crystals By Ascending U-type Ampoule Method

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 detectγ-ray orα-ray among 1keV～1MeV, good energy resolution can be observed. So far, there are many oversea reports about PbI₂, which mainly focuses on PbI₂ crystal growth and fabrication of detector, while the synthesis of PbI₂polycrystal and the growth single crystal technique have not been studied carefully, so the as grown crystal and the detector fabricated from are not satisfactory. In our country, there has a little report. The aim of this paper is to explore a new growth method of PbI₂ single crystal with high quality and large size, and to lay a foundation for detector fabrication.There are two problems on PbI₂ crystal growth by Vertical Bridgman Method, the evaporation and refluence of iodine, the separation and precipitation of lead. Aimed at this situation, a new U-type ampoule has been designed in this paper. By adjusting the height of liquid in U-type ampoule, eliminating the space at the top of PbI₂ melt, the decomposition PbI₂ melt has been avoided, then the evaporation and refluence of iodine restrained, too. Meanwhile the ascending U-type ampoule method has been employed to maintain the crystallization basipetally, make the segregated lead from PbI₂ melt deposit to the bottom of crucible with the help of gravity, so PbI₂ single crystal with good quality has been obtained. The as grown PbI₂ crystal with 15mm in diameter and 35mm in length is intact and translucent with yellow appearance, resistivity of 10¹³Î©Â·cm magnitude, bandgap of 2.27eV, and infrared transmittance of about 45%. At last, the 59.5 keVγ-ray peak of ²⁴¹Am has been measured with PbI₂ detector fabricated with as grown crystal.