Design and modelling of anisotropic thin film light-emitting devices with the plane wave expansion method

摘要

In most emitting materials the dipole moments are distributed in an isotropic way, and light is emitted in all directions (modified by interference in the OLED layers). But the radiation of each individual dipole is directed around the equatorial plane of the dipole moment. By analyzing the photoluminescent decay times in different microcavities, a phosphorescent emitter with an anisotropic distribution of 80% in-plane dipoles is demonstrated. Simulations show that if all dipoles are arranged in-plane with the OLED layers the outcoupling efficiency to air would improve from 20% to 30%. Anisotropic emitters can be combined with known outcoupling techniques like microlens foils to provide even higher outcoupling efficiencies. With a fully oriented emitter nearly 70% of the light is reaches the OLED substrate where it is available for extraction by outcoupling foils. When organic laser dye molecules are dissolved into the CLC, a laser can be made. A CLC film supports a resonant standing wave for wavelengths at the edge of the bandgap. When the dye molecules are pumped above the lasing threshold by a pulsed shorter wavelength pump laser, longer wavelength laser light is emitted perpendicular to the CLC film. The thickness of the CLC film is around 10μm. Laser emission has been shown across the entire visible spectrum employing different dye molecules. The emission wavelength can also be tuned across ranges of about 50nm in different ways. However CLC lasers are still hindered by high lasing thresholds and low output power, as well as bleaching of the dye molecules. In this work the light emitting properties of CLC films are simulated with the anisotropic plane wave expansion method both for spontaneous and stimulated emission. The measured emitted spectrum at different angles and polarization are accurately modelled by the plane wave expansion. A model for estimating the gain threshold and laser wavelength of CLC films was developed and verified by experiment. Optical amplification is treated by introducing gain terms to the refractive index. This model may prove a valuable tool to design more advanced liquid crystal lasers.