"Photogenerated Triplet Excitons for Photon Upconversion and Spin-polarization in QD-molecular Nanostructures"
Abstract:  Semiconductor nanocrystals, or quantum dots (QDs), offer direct optical access to photogenerated triplet excited states for photon upconversion and spin-active excited states. This is important for energy conversion or quantum information science (QIS). QDs are excellent triplet photosensitizers because their synthetically tunable absorption profile usually comes with a large extinction coefficient, accessible with steady-state light sources at moderate temperatures. In this talk, I will describe how our initial foray into using QDs as light absorbers for photon upconversion via triplet-triplet annihilation, has lead us to explore different classes of materials for QIS applications. Our work designing conjugated organic ligands to enhance triplet energy transfer from chalcogenide QDs for the efficient conversion of near-infrared photons to visible light, has motivated research into silicon QDs. Compared to chalcogenide nanocrystals, silicon is non-toxic and earth-abundant. Silicon’s low spin-orbit coupling can support spin-polarization in organics. Using Si QDs synthesized with a scalable non-thermal plasma, with pulsed EPR spectroscopy, we can generate, study and manipulate the spins in these hybrid Si:QD-acene nanostructures to photogenerate spin polarized molecular triplet states or spin-correlated radical pairs (SCRPs). These highly tailorable inorganic-organic hybrid systems offer versatility, stability and expanded access to spin-active excitons compared to traditional all-organic donor-acceptor systems.