A hybrid material that pairs organic semiconductors with lanthanide-doped nanoparticles can swap spins and transfer energy between the two components, giving researchers a new way to control triplet excitons—long-lived, spin-1 excited states that are normally difficult to harness. Triplet excitons are central to technologies from LEDs to photocatalysis, but their spin properties make them hard to manipulate. Current methods for controlling triplet dynamics are limited. The researchers recently showed that when organic molecules and lanthanide nanoparticles are brought together, the molecular spin couples to unpaired spins on the lanthanide ions, and energy can flow in both directions between triplet excitons and the ions. This opens a fundamentally new route to steer triplet behaviour. If successful, the project will build a mechanistic understanding of this spin-exchange coupling and energy transfer, then use that knowledge to design materials with optimised properties. The team will demonstrate proof-of-concept devices: near-infrared LEDs and optically pumped lasers emitting at 1300–1600 nm, and systems that convert near-infrared light to blue light at very low excitation powers—potentially triggering chemical reactions in biological environments. Broader applications could include photocatalysis, optoelectronics, 3D printing, and optogenetics.
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SPICE will deliver a new paradigm for the control of spin-1 triplet excitons. The starting point for SPICE is our recent discovery that in hybrid systems of organic semiconductors and lanthanide-doped inorganic nanoparticles it is possible to spin-exchange couple the molecular spin to the unpaired spins on the Ln3+ ions and to transfer energy from triplet excitons to Ln3+ and vice versa (Han et al., Nature 2020). This opens a fascinating area for exploration and discovery, as well as routes to control triplet dynamics in ways not possible via current methods. SPICE will combine steady-state and ultrafast optical spectroscopy with molecular and lanthanide nanoparticle design to explore these new phenomena and build a comprehensive mechanistic understanding of spin- exchange coupling and energy transfer at the organic-lanthanide nanoparticle interface and make proof of concept demonstrations of novel materials and device functionalities. Key aims will be: 1) Building structure-function relationships to understand the mechanisms of:(a) spin-exchange mediated brightening of the normally forbidden S0-Tn transitions; (b) spin-exchange mediated enhancement of intersystem crossing (S1-T1) rates; (c) energy transfer from triplet excitons to Ln3+ and vice versa; (d) the triplet-Ln fusion process (T1+Ln-S1) to give upconverted emission and the hybrid Ln-Organic electronic states that must mediate this process. 2) We will then use the insights generated to develop new materials with optimised energy transfer and emission properties. 3) Finally, we will make proof of demonstrations of LEDs and optically pumped lasers with NIR emission (1300-1600nm) and NIR to blue upconversion at very low excitation powers that can trigger chemical reactions in biological environments. The success of SPICE would open new avenues to harness triplet excitons that could find transformative applications in areas ranging from photocatalysis and optoelectronics to 3D printing and optogenetics.
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