Ultrafast fluorescent decay induced by metal-mediated dipole-dipole interaction in two-dimensional molecular aggregates

Two-dimensional molecular aggregate (2DMA), a thin sheet of strongly interacting dipole molecules self-assembled at close distance on an ordered lattice, is a fascinating fluorescent material. It is distinctively different from the single or colloidal dye molecules or quantum dots in most previous research. In this paper, we verify for the first time that when a 2DMA is placed at a nanometric distance from a metallic substrate, the strong and coherent interaction between the dipoles inside the 2DMA dominates its fluorescent decay at picosecond timescale. Our streak-camera lifetime measurement and interacting lattice-dipole calculation reveal that the metal-mediated dipole-dipole interaction shortens the fluorescent lifetime to about one half and increases the energy dissipation rate by ten times than expected from the noninteracting single-dipole picture. Our finding can enrich our understanding of nanoscale energy transfer in molecular excitonic systems and may designate a new direction for developing fast and efficient optoelectronic devices.Comment: 9 pages, 6 figure

Force on a single slat during the start-up process of a fluidized bed

Internal baffles made of multiple slats are widely employed in the industrial fluidized-bed reactors to split bubbles and improve lateral bubble distribution to enhance gas-solids contact, and meanwhile suppress gas/solids back-mixing to optimize their residence time distributions, and ultimately to achieve good product selectivity and higher profitability. However, as fluidized-bed reactors are often required to be operated continuously for years, the long-period reliability of the baffles immersed in bed is also an important issue. Therefore, detailed information of forces acting on the baffles under different operating conditions is very important for their proper structure and strength design. During our past cold model experiment, we once found by chance that a steel probe with OD 20 mm was bent in a fluidized bed of ID 800 mm during the start-up process of the bed. This indicates a high short-term force and a potential danger during the start-up period of the bed, e.g. when sudden power-down or stopping of the blower happens, that may impair the reliability of immersed baffles in industrial fluidized reactors. In this study, we investigated the force acting on a tested slat during the start-up process of a fluidized bed systematically. The experiment was carried out in a cold model fluidized bed with a square cross section of 300 mm×300 mm. The solids material in the fluidized bed was silica sand particles belonging to typical Geldart B particles. A horizontal slat of 50 mm (height) ×300 mm (width) ×2 mm (thickness) was immersed in the bed during tests. The force acting on the slat was measured by adhering two strain gauges on the surface of both ends of the slat. The influencing factors considered in this study included superficial gas velocity, inclination angle and installation height of the slat. Please click Additional Files below to see the full abstract