High-resolution fluorescence imaging of isolated nanoparticles of a common semiconducting polymer (poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene, MEH-PPV), produced by ink-jet printing techniques, has revealed highly uniform transition moment orientation perpendicular to the glass substrate. In contrast with the broad emission spectra associated with bulk or single molecules of these species in thin films, we observe narrow photoluminescence emission spectra (10-15 nm fwhm) from individual oriented polymer nanostructures with no evidence of spectral diffusion on time scales of several hundred seconds. The distribution of center frequencies (from several hundred individual nanoparticle measurements) shows clearly defined peaks that can be correlated with excitonic traps of integer multiples of monomer conjugation lengths (8, 9, 10, and 11). The observation of discrete emission characteristics in this important class of materials suggests exciting possibilities in photonics and molecular optoelectronics.

Poly(ethylene glycol) [PEG] microparticles were doped with ceramic or latex nanoparticles in order to examine domain-size and refractive index effects of nanometer-sized guest inclusions on two-dimensional diffraction patterns. Composite microparticles were examined for different inclusion sizes and polymer/nanoparticle weight ratios in order to determine the size and number-density threshold of detection for guest nanoparticles within the polymer host as indicated by fringe distortion in 2-D angular scattering. PEG host particles having a 10 μm (nominal) diameter were formed with three different guest nanoparticles (Al2O3, TiO2, and latex nanospheres with respective sizes of 46, 29, and 14 nm). For the ceramic nanoparticle inclusions, distortion was observed at relative guest−host weight fractions of 5−10%. For the 14 nm latex inclusions, no distortion was observed at any weight fraction. A perturbation method was used to simulate the effect of nanometer-size inclusions on 2-D optical diffraction from polymer host microparticles and to suggest how the distortions should vary with inclusion size, refractive index, and number.