Fluorescence of a dye-doped cholesteric liquid crystal film in the region of the stop band: theory and experiment

Due to the sinusoidal modulation of the dielectric properties along the helical axis, cholesteric liquid crystals exhibit a photonic stop band for circularly polarized light, which strongly affects the emission of fluorescent guest molecules. In this paper, we discuss the resulting changes in the emission spectrum. In an analytical treatment, we first derive the photonic densities of states of the two normal light modes for propagation parallel to the helical axis, taking into account multiple reflections due to the finite film thickness. Then we discuss the influence of the degree of order of the dye's transition dipole moment on the emission characteristics. Finally, we present experimental results. which show excellent quantitative agreement with our theoretical description.