| Abstract [eng] |
The increasing demand for organic systems capable of incoherent NIR (>700 nm) photon upconversion (UC) is stimulated by a growing variety of applications such as 3D printing, photocatalysis, bioimaging, photovoltaics and many more. The higher energy upconverted emission from an emitter emerges through a process called triplet-triplet annihilation (TTA) sometimes also referred to as triplet fusion. Currently, the NIR-to-Vis TTA-UC suffers from low efficiency, particularly in the solid-state, which in turn hinders practical applications. The best-performing NIR-to-Vis UC systems demonstrated so far, both in solution and solid state, rely on the rubrene (Rub) emitter. However, there are challenging unresolved issues related to Rub. The aim of this dissertation is to investigate UC systems based on the benchmark emitter rubrene both in solution and solid-state and identify the limiting factors hindering the UC performance. In this work we observed that a key factor limiting UC efficiency in NIR-to-Vis UC system based on Rub emitter is it’s low statistical probability ( f ) to obtain a singlet state from two triplets via TTA. By modifying Rub we investigate the changes induced to the UC performance in solution and in solid-state. We also investigate the emissive properties of Rub films under various deposition modes, optimize solid-state UC films and fully characterize them by measuring various properties related to UC including singlet and triplet exciton diffusion. |
