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Photoluminescence from MEH-PPV and DP-PPV in bulk and encapsulated in porous alumina Qi, Dong Feng

Abstract

Two PPV derivatives, MEH-PPV and DP-PPV, are encapsulated in the nanopores of anodized alumina with different pore sizes (50/200 nm) and depth (10/60 urn). Time-integrated and time resolved optical emission properties of these structures have been studied and compared with those of thin films of the polymers. Significant blue shifts of the PL spectra (0.034 eV-0.183 eV) are found in the porous materials as compared to the bulk. The relative intensity of the one-phonon assisted transition increases in comparison with the intensity of the no-phonon transition in the nanostructured samples. The time constants of the optical emission from the bulk MEH-PPV film are very similar in their energy dependence to results obtained previously on bulk PPV films when considered with respect to the excess energy above the peak of the emission spectrum. The decay times are, however, two to three times shorter in the parent. The energy dependence of the time constants measured in DP-PPV films and DP-PPV encapsulated in nanopores (pore diameter 200 nm, pore depth 60 um) are also very similar to each other, and to the results obtained on the MEH-PPV. These results suggest that the intrachain diffusion of electron-hole excitations in all of these polymers, either in bulk or encapsulated form, is very similar.

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