Metal nanoparticles separated by nanogap spacings generate a significantly enhanced electromagnetic field caused by the light-induced localized surface plasmon resonance. This enhanced electromagnetic field, so-called a hot spot, amplifies the optical absorption and emission of dye molecules in nanogaps. In this study, we fabricated large-area plasmonic Au nanogap arrays with highly integrated hotspots by utilizing the spontaneous nanophase separation of block copolymers. These arrays showed the amplification of upconversion emission based on solid-state triplet-triplet annihilation (TTA-UC).
Localized surface plasmon resonance (LSPR) of noble metal nanoparticles is an optical phenomenon to enhance the electro-magnetic field near a particle and has the potential to enhance the performance of solid-state triplet-triplet annihilation photon upconversion (TTA-UC). In order to fully utilize an enhanced electro-magnetic field generated by LSPR, the spatial arrangement of dye molecules near noble metal nanoparticle plays an important role. In this study, donor and acceptor molecules are sequentially introduced on the plasmonic nanoparticles and investigated the correlation between the spatial arrangement of dye molecules and the UC enhancement behavior in solid-state TTA-UC.
Improving efficiency of triplet–triplet annihilation-based photon upconversion (TTA-UC) in crystalline media is challenging because it usually suffers from the severe aggregation of the donor (sensitizer) molecules in acceptor (emitter) crystals. We show a kinetically controlled crystal growth approach to improve donor dispersibility in acceptor crystals. As the donor–acceptor combination, a benchmark pair of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA) is employed. A surfactant-assisted reprecipitation technique is employed, where the concentration of the injected PtOEP–DPA solution holds the key to control dispersibility; at a higher PtOEP–DPA concentration, a rapid crystal growth results in better dispersibility of PtOEP molecules in DPA crystals. The improvement of donor dispersibility significantly enhances the TTA-UC quantum yield. Thus, the inherent function of donor-doped acceptor crystals can be maximized by controlling the crystallization kinetics.
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