Circularly polarized luminescence from chiral thin films

摘要

Photoluminescent nanostructured thin films have been fabricated using physical vapour deposition and the glancing angle deposition (GLAD) technique. Precision controlled substrate motion and oblique incidence (>75°) enable the fabrication of a variety of 3-D morphologies including vertical posts, helical (chiral) columns and chevrons. Scanning electron microscopy and X-ray diffraction were used to characterize the film nanostructure. These experiments focussed on the chiral morphology which exhibits intriguing polarization behaviour such as selective transmission of circularly polarized light and circularly polarized photoluminescence. Helical films of Y_2O_3:Eu and Alq_3 were fabricated with thicknesses in excess of 2 μm and densities nominally 60% of bulk. Transmission spectroscopic ellipsometry measurements were used to determine the degree of selective transmission of polarized light through the samples. The degree of circular polarization for the photoluminescent light emitted from helical films was measured with the use of a quarter waveplate and linear polarizer. Polarized photoluminescence efficiencies were consistent with the observed selective transmission of circularly polarized light through the films. The use of GLAD to control the nanoscale morphology of the films allows for the spectral location and strength of these polarization effects to be easily and accurately selected.