Hard Radiation Detection from the Selenophosphate Pb₂P₂Se₆

The heavy metal selenophosphate, Pb₂P₂Se₆, is a promising new material for cost-effective X-ray/γ-ray detection. Crystal boules of Pb₂P₂Se₆ up to 25 mm in length and 15 mm in diameter are grown by a vertical Bridgman method. They are cut and processed into size-appropriate wafers for physical, photo-transport property studies, as well as γ-ray detector testing. The material is a semiconductor with an indirect bandgap of 1.88 eV and has electrical resistivity in the range of 1 × 10¹⁰ Ω cm. Pb₂P₂Se₆ single crystal samples display a significant photoconductivity response to optical, X-ray, and γ-ray radiation. When tested with a ⁵⁷Co γ-ray source, Pb₂P₂Se₆ crystals show spectroscopic response and several generated pulse height spectra resolving the 122.1 and 136.5 keV ⁵⁷Co radiation. The mobility-lifetime product of Pb₂P₂Se₆ is estimated to be ≈3.5 × 10^-5 cm² V^-1 for electron carriers. The Pb₂P₂Se₆ compound melts congruently at 812 °C and has robust chemical/physical properties that promise low cost bulk production and detector development. Wide bandgap selenophosphate Pb₂P₂Se₆ is identified as a cost-effective X-ray and γ-ray detector material. The crystal growth of Pb₂P₂Se₆ and characterizations in terms of its optical, electrical, thermal, and mechanical properties are reported. A Pb₂P₂Se₆ single crystal detector is able to resolve ⁵⁷Co radiation.