(708d) Investigating Colloidal PbSe Quantum Dots As a Room Temperature Operating Material for Gamma Ray Spectroscopy

Semiconductor diode radiation detectors serve as the industry standard for gamma ray spectroscopy. Most of these are fabricated with high-purity germanium (HPGe) single crystals, where energy resolution below 1% can be obtained for 662 keV gamma rays (Cs-137). Despite the maturity of this technology, it has several drawbacks. HPGe detectors need to be operated at liquid nitrogen temperatures and are costly to produce due to the required high purity of the single crystals. Developing a gamma ray semiconductor detector that can operate at room temperature, while matching industry standard resolution has been a challenge. Recently it was proposed that PbSe colloidal quantum dots (QDs) can be used to make low-cost gamma ray detectors, which allow gamma ray spectroscopy to be performed. PbSe has an exciton Bohr radius of 46 nm, which allows the exploitation of quantum confinement effects to tune electronic and optical properties. Synthetic methods to control the diameter and composition of PbSe colloidal QDs have been demonstrated where the electronic and optical properties can be precisely tuned. PbSe QDs also exhibit multiple exciton generation (MEG) through impact ionization (II) where more than one exciton can be produced by one interaction with ionizing radiation. These properties make PbSe QDs a strong candidate as a room temperature gamma ray detector. In this study, we have developed a microwave assisted synthetic protocol for PbSe QDs. The PbSe QDs were characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, UV-Vis-NIR spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. We found that the QDs were spherical and the diameters could be controlled to between 4-8 nm. QD based devices were fabricated with as synthesized, or ligand exchanged material, and electronically characterized. Their response to gamma radiation was monitored using a linear pulse circuit and multiple channel analyzer.