Photoluminescent Energy Transfer from Poly(phenyleneethynylene)s to Near-Infrared Emitting Fluorophores

Photoluminescent energy transfer was investigated in conjugated polymer-fluorophore blended thin films. A pentiptycene-containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission and the enhancement of the fluorophore emission. Near-infrared emitting squaraines and terrylenes were identified as excellent energy acceptors. These results, where a new fluorescent signal occurs in the near-infrared region on a completely dark background, offer substantial possibilities for designing highly sensitive turn-on sensors.National Institute of General Medical Sciences (U.S.) (F32GM086044)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (DAAD-19-02-0002

Scattering of long wavelengths into thin silicon photovoltaic films by plasmonic silver nanoparticles

Nanoparticles and nanostructures with plasmonic resonances are currently being employed to enhance the efficiency of solar cells. Ag stripe arrays have been shown theoretically to enhance the short-circuit current of thin silicon layers. Monolayers of Ag nanoparticles with diameter d < 300 nm have shown strong plasmonic resonances when coated in thin polymer layers with thicknesses < d. We study experimentally the diffuse vs. specular scattering from monolayer arrays of Ag nanoparticles (spheres and prisms with diameters in the range 50 – 300 nm) coated onto the front side of thin (100 nm < t < 500 nm) silicon films deposited on glass and flexible polymer substrates, the latter originating in a roll-to-roll manufacturing process. Ag nanoparticles are held in place and aggregation is prevented with a polymer overcoat. We observe interesting wavelength shifts between maxima in specular and diffuse scattering that depend on particle size and shape, indicating that the nanoparticles substantially modify the scattering into the thin silicon film.United States. Air Force (United States. Army. Natick Soldier Research Development and Engineering Center Contract FA8721-05-C-0002)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-07-D0004