9 research outputs found
Novel cholesteric materials doped with CdSe/ZnS quantum dots with photo- and electrotunable circularly polarized emission
International audienceOptical materials based on cholesteric liquid crystals (LCs) doped with fluorescent CdSe/ZnS quantum dots (QDs) have been developed and demonstrated to have a wide photonic band gap. It has been shown that the fluorescence emission of QDs embedded in LCs is circularly polarized and that the dissymmetry factor of this polarization may be optically or electrically controlled via conformational changes in the helical structure of the LC matrix. The possibility of photochemical patterning or image recording using these materials has been demonstrated; the recorded information can be read through changes in the dissymmetry factor of circular polarization of QDs emission. The developed photo- and electro-active materials with a controlled degree of fluorescence circular polarization may be used as on-demand single photon sources in photonics, optoelectronics, and quantum cryptography, as well as for development of nanophotonic systems capable of low-threshold lasing
Direct Observation of Changes in Focal Conic Domains of Cholesteric Films Induced by Ultraviolet Irradiation
The
helical supramolecular structure of cholesteric liquid crystalline
(LC) films predetermines their outstanding optical properties and
the unique nanostructure of their surface. The introduction of photochromic
dopants in these films opens up an interesting possibility for creation
of smart cholesteric materials with photocontrollable optical and
photovariable surface properties. Using atomic force microscopy (AFM),
we performed <i>in situ</i> measurements of the surface
topography of cyclosiloxane LC cholesteric oligomer films during the
cholesteric helix twisting caused by their preliminary ultraviolet
(UV) irradiation. A chiral-photochromic isosorbide-based dopant was
introduced in the films to control the cholesteric helix pitch by
UV-irradiation. The initial films are characterized by planar texture
with the presence of focal conic domains having the double-spiral
relief on their surface. UV-irradiation of these films leads to the
cholesteric helix twisting resulting in a decrease in the surface
relief period, and the enlargement of defect areas between the domains.
The detailed mechanisms of the rearrangement of the film surface structure
due to the cholesteric helix twisting are suggested. They include
the rotation and displacement of cholesteric layers in the bulk, and
the nucleation of new ones at the surface in defect regions