Low-Voltage and Highly Sensitive PbS Quantum Dot Thin-Film X-ray Monitors

In the past decade, lead sulfide quantum dots (PbS QDs) have been widely adopted for the fabrication of visible and infrared photodetectors, thanks to their unique properties such as a wide range of band gap tunability, high optical absorption, easy processability, as well as mechanical flexibility. Such characteristics may be also desirable for the realization of high-energy detectors, and the high atomic number of Pb suggests that PbS QDs could be effectively employed also at X-ray wavelengths. Here, we propose PbS QDs as a sensing material for X-ray detection. A homogeneous population of colloidal PbS QDs (3-4 nm) was synthesized with high purity and good yield (>70%) through a low-cost synthetic route. The colloidal solution of PbS QDs showed chemical and physical stabilities for over 6 months. A PbS QDs thin layer of about 2 mu m thickness was obtained through a simple drop-casting deposition and slow evaporation. The device exhibited high sensitivity (2370 mu C Gy(-1) cm(-2)) and a good detection limit of 5 mu Gy s(-1) to 23 keV hard X-rays at a 1 V bias. Such encouraging results pave the way for the use of PbS QD-based X-ray sensors for imaging applications, suggesting also future developments of low-power and high-sensitivity wearable sensors.