(Invited) Reshaping Light with Hybrid Quantum Dot: Molecule Systems

Photon upconversion is an energy conversion process wherein a material absorbs two or more low-energy photons and uses their energy to generate high-energy photons. Upconversion systems that convert near-infrared light into the visible range can address current challenges in solar energy capture and near-infrared sensor design while materials that operate at higher energy, producing UV photons from visible light, can enable applications in photocatalysis and light-based 3D printing. Due to their high extinction coefficients and size-tunable optical properties, quantum dots have emerged as ideal photosensitizers for photon upconversion systems. In these systems, light absorbed by a quantum dot is passed to a molecule at its surface, placing the molecule into a spin-triplet state. Upconversion is achieved when two molecules in their triplet state encounter one another and undergo triplet fusion, a process that deexcites one molecule and promotes the other to a high-energy, emissive spin-singlet state. In this presentation, I will present spectroscopic measurements and electronic structure calculations that identify energy transfer rates and key intermediates involved in two quantum dot systems that respectively demonstrate red-to-blue and blue-to-UV photon upconversion. In the first system, which consists of silicon quantum dots functionalized with anthracene ligands, we find that by controlling the chemical structure of molecular tethers that covalently link anthracene to silicon, we can produce strongly coupled states wherein excited charge carriers are shared between silicon and anthracene. By controlling the energy of these states, we can optimize the system’s performance, achieving an upconversion quantum yield of 17.2%. In the second system, we use CsPbBr 3 perovskite quantum dots to drive triplet energy transfer to naphthalene ligands. This energy transfer process is found to be highly sensitive to the structure of the chemical linker that binds naphthalene to CsPbBr 3 , which we attribute to modulation of the degree of wavefunction overlap between the states of the quantum dot energy donor and naphthalene energy acceptor.