title: Assessment of Anisotropic Semiconductor Nanorod and Nanoplatelet Heterostructures with Polarized Emission for Liquid Crystal Display Technology.
abstract: Semiconductor nanorods can emit linear-polarized light at efficiencies over 80%. Polarization of light in these systems, confirmed through single-rod spectroscopy, can be explained on the basis of the anisotropy of the transition dipole moment and dielectric confinement effects. Here we report emission polarization in macroscopic semiconductor-polymer composite films containing CdSe/CdS nanorods and colloidal CdSe nanoplatelets. Anisotropic nanocrystals dispersed in polymer films of poly butyl-co-isobutyl methacrylate (PBiBMA) can be stretched mechanically in order to obtain unidirectionally aligned arrays. A high degree of alignment, corresponding to an orientation factor of 0.87, was achieved and large areas demonstrated polarized emission, with the contrast ratio I∥/I⊥ = 5.6, making these films viable candidates for use in liquid crystal display (LCD) devices. To some surprise, we observed significant optical anisotropy and emission polarization for 2D CdSe nanoplatelets with the electronic structure of quantum wells. The aligned nanorod arrays serve as optical funnels, absorbing unpolarized light and re-emitting light from deep-green to red with quantum efficiencies over 90% and high degree of linear polarization. Our results conclusively demonstrate the benefits of anisotropic nanostructures for LCD backlighting. The polymer films with aligned CdSe/CdS dot-in-rod and rod-in-rod nanostructures show more than 2-fold enhancement of brightness compared to the emitter layers with randomly oriented nanostructures. This effect can be explained as the combination of linearly polarized luminescence and directional emission from individual nanostructures.
authors.affiliation: Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States.
authors.forename: Patrick D
authors.initials: PD
authors.lastname: Cunningham
authors.affiliation: Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States.|Instituto de Química de São Carlos, Universidade de São Paulo-USP, Colloidal Materials Group , CP 780, 13566-590 São Carlos, São Paulo, Brazil.
authors.forename: João B
authors.initials: JB
authors.lastname: Souza
authors.affiliation: Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States.
authors.forename: Igor
authors.initials: I
authors.lastname: Fedin
authors.affiliation: Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States.
authors.forename: Chunxing
authors.initials: C
authors.lastname: She
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Byeongdu
authors.initials: B
authors.lastname: Lee
authors.affiliation: Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States.|Center for Nanoscale Materials, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Dmitri V
authors.initials: DV
authors.lastname: Talapin
keywords: liquid crystal display; nanoplatelets; nanorods; polarized luminescence; quantum dots; semiconductor nanocrystals