Lead iodide platelets: correlation between surface, optical and electrical properties with X and γ ray spectrometric performance

Lead iodide platelets grown by Physical Vapor Deposition were characterized by several properties related to spectrometric performance. Platelets were grown from both synthesized lead iodide without purification and then purified by repeated evaporation. The growth was performed by heating the starting material at vacuum (10^-5 mmHg) or in high purity Ar atmosphere (500 mmHg) at temperatures from 390 to 430°C, during 5 to 20 days. Platelets grew at 200-250°C and perpendicular to the ampoule wall. Platelet size is up to 13×8 mm² and their thickness is from 50 to 100 μm. Crystals were characterized by optical microscopy, atomic force microscopy, scanning electron microscopy and low temperature photoluminescence. These characterizations showed that platelets have an exceptional transparence, that they grew from hexagonal grains and that their surface has a mean roughness of 4.6 nm. Low temperature photoluminescence was performed: peak position and broadness confirmed the high purity of the starting material and bands confirmed strong components from free and bonded excitons and low superficial imperfections ((Iex/Iimp)=6). Electrical properties were measured by fabricating radiation detectors with front palladium thermal deposition contacts and acrylic encapsulation. Resistivities of about 5×10 ¹³ Ω. cm and current densities of 50 pA/cm² (10 V) were obtained. X-ray spectroscopy was performed with lead iodide detectors and an energy resolution of 1.2 keV was achieved for ²⁴¹ Am 18 keV radiation. Correlation between optical and surface properties and electrical parameters and detector performance are presented. Also, the different results were compared with previous ones for crystals grown by other methods and with alternative materials