Controlling the Synthesis of Colloidal Lead Selenide Quantum Dots

Henry B. Anderson¹, Audrey O. Darus¹, Tyler D. McCrea¹, Gregory S. Herman¹, Haori Yang²

¹School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR, USA.

²School of Nuclear Science and Engineering, Oregon State University, Corvallis, OR, USA.

Room temperature semiconductor detector (RTSD) materials for radiation sensing are of considerable research interest. This is due to their potential to compete with the resolution of the current industry standards for radiation sensing while also decreasing the cost of production and operation. One promising material for developing RTSDs is colloidally suspended lead selenide quantum dots (PbSe QDs). Its many favorable properties include a large exciton Bohr radius of 46 nm, a tunable band gap between 0.28-1.3 eV, and an ability to exhibit multiple exciton generation. In this study, we developed a consistent synthetic protocol to produce lead selenide quantum dots with tris(diethylamino)phosphine and oleic acid ligands and showed a correlation between the particle size and the first exciton absorption peak. Particle size was varied by changing reaction temperature and holding time. Reaction temperatures between 120 ⁰C and 150 ⁰C and holding times between 3 minutes and 7 minutes were used. A MARS V microwave was used to heat the reactants and characterization was performed using transmission electron microscopy, UV Vis-NIR spectroscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. We found that our synthetic protocol is capable of consistently producing QDs with a size ranging from 3-6 nm with good uniformity in shape, expected atomic ratio and the expected clausthalite crystalline structure. By comparing the quantum dots size to the position of their first exciton absorption peak, we were able to develop a strong correlation showing that a red shift in the peak occurs with increasing nanoparticle size. With the development of this synthetic protocol, lead selenide quantum dots can now be implemented into RTSD devices to test their radiation sensing properties, and an investigation of their surface passivation over time by the tris(diethylamino)phosphine and oleic acid ligands can be performed using X-ray photoelectron spectroscopy.