Influence of doping and non-stoichiometry on the quality of lead iodide for use in X-ray detection

Abstract Lead iodide (PbI 2 ) crystals were synthesized with stoichiometric composition and with an excess of iodine or lead. Crystals were further doped by Ag, Au, Ge, and a number of rare-earth elements (RE). The structure of the crystals was analyzed by high resolution X-ray diffractometry (HRXRD) and electron backscatter diffraction (EBSD). The rocking curves measured by HRXRD confirm the crystal quality and EBSD measurements present the progress of sample preparation. Crystals have further been investigated by measuring electrical resistivity, low temperature photoluminescence, and optical transmission. Stoichiometric composition or that with low excess of lead has been shown to give best quality crystals. Doping with Ag leads to considerable decrease of electrical resistivity and at the same time gives optical gap as high as that of undoped samples. Doping with RE generally leads to the decrease of optical gap due to band tailing induced by lattice distortions. Low level RE doping in same cases (Ho, Tm) leads to pronounced gettering, thus giving high electrical resistivity and narrow PL bands.