(138f) Elucidating the Origin of Intra-Band Optical Transitions in Ag2se Colloidal Quantum Dots and Their Potential Utilization for Infrared Detectors

In the past 30 years, material scientists have largely capitalized on the grand appeal of utilizing quantum confinement to obtain size-tunable inter-band optical transitions and implement colloidal quantum dots (CQDs) in optoelectronic applications throughout the electromagnetic spectrum. The infrared region is particularly exciting with applications in telecommunications, night-time surveillance, and satellite imaging for agricultural water conservation. While most progress with CQDs in the infrared (IR) has been achieved using inter-band transitions in Pb- and Hg-based heavy metal compounds, intra-band optical transitions originating from external- or self- dopants can potentially expand the library of materials to generate IR-optoelectronic devices with non-toxic materials. In this talk, I will focus on my group’s work on recently discovered silver chalcogenide (Ag₂Se) quantum dots that exhibit distinct optical absorption in the mid-IR wavelength spectrum. These CQDs demonstrate a narrow bandgap metastable tetragonal phase, not available in bulk, and contain excess electrons in the lowest level of the conduction band. This allows for intra-band optical transitions between the first and the second conduction energy level which can significantly decrease Auger recombination rates and avoid the need for cryogenic cooling. I will present a detailed study of the size-dependent inter-band to intra-band optical transition and compare the competing effects of quantum confinement, environmental Fermi level and particle stoichiometry to provide guidelines for stable electron occupation of the 1S_e state and obtaining tunable MWIR absorption.