| Glancing angle deposition (GLAD) can be used to fabricate unique, nanostructured thin films that exhibit intriguing optical properties because the characteristic length scale of the nanostructures is on the order the wavelength of visible light. Previous studies of the optical properties of such films have focused upon the light transmitted, reflected, or scattered by the nanostructures. Here, the optical properties of luminescent chiral thin films were explored. Following the initial structural and optical characterization of simple nanostructured thin films, chiral thin films were shown to exhibit a one-dimensional photonic stop band for one handedness of circularly polarized light, also known as circular Bragg phenomena, for both transmittance experiments and photoluminescence experiments. First inorganic, then organic photoluminescent materials were used to fabricate the luminescent chiral thin films studied, with europium-doped yttrium oxide (Y2O3:Eu) serving as the inorganic photoluminescent material and tris-(8-hydroxyquinoline) aluminum (Alq3) serving as the organic photoluminescent material. Porous chiral Y2O 3:Eu films were fabricated and found to emit partially circularly polarized light in photoluminescence. The highest degree of circular polarization measured for these chiral Y2O3:Eu was ∼ 5%. The chiral Alq 3 films constituted the first directly deposited porous nanostructured organic films produced by GLAD. They were found to consist of a nearly hexagonal close-packed array of smooth, uniform helical structures. These structures, which do not tend to broaden with increasing thickness, were used to fabricate samples which exhibited strong circular Bragg phenomena with the degree of circular polarization of light emitted by chiral Alq3 films reached a magnitude of ∼ 71%. The remarkable structural and optical properties of nanostructured Alq3 films suggest that novel, directly deposited porous nanostructured organic films will find uses in many applications both within the field of photonics and beyond. |
