Liquid crystal (LC) materials with negative dielectric anisotropy have been successfully applied to light emitting diode. Even for a nematic phase, the Fredericks transition was avoided under such a strong electric field as used in organic light emitting diode (OLED). The LC materials having shallower highest occupied molecular orbital (HOMO) levels have been emissive due to their higher probability for hole injection. The LC materials incorporated three fluorescent dyes for each color (R,G,B) show corresponding color emission. However, only blue dye shows extraordinarily small light emission. Relative fluorescence quantum yield measurement reveals similar fluorescence efficiency for all dyes. Only blue dye’s HOMO level lies very close to that of the matrix LC. This fact may lead to very small hole trapping probability for the blue dye molecule. It is suggested that in the OLED system using LC materials studied here, the recombination of the electrons and the holes trapped at the dye molecules is dominant for light emission rather than Foerster energy transfer.
A new type of liquid crystal device was developed by applying a concept of liquid crystal phase gratings (LCPGs). LCPGs are composed of square-wave phase gratings constructed with poly(methyl methacrylate) and liquid crystals which fill the grating grooves. The typical sizes of the phase grating are 10 micrometers in width and 2 micrometers in depth. The transmitted light wavelength can be easily controlled by changing applied voltage. The transmittance varied from less than 1 for monochromatic polarized light, when applied voltage varied from 0 V to 5 V. Rise times for the light varied from 0.2 ms to 7 ms with applied voltage, and were inversely proportional to the square of the applied voltage. Decay times, which depend slightly on the applied voltage, were about 4 ms. A transmitted light, i.e., an observed color (e.g., R,G,B and white), was dependent on not only applied voltage but also grating depth. When two of the LCPGs were combined in such a way that their grating lines were oriented perpendicular to each other, these LCPGs were applicable to nonpolarized light.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.