Angular-Dependent Spontaneous Emission in Cholesteric Liquid-Crystal Films

Because of the presence of a selective reflection band, cholesteric liquid crystals strongly modify the emission of fluorescent guest molecules. While emission along the helical axis is well understood, the emission properties at oblique angles with respect to the cholesteric helix have so far not been explored in detail. We present a systematic study of the angular-dependent spontaneous emission properties of dye-doped cholesteric films, including a full Stokes analysis of the emitted light. Variation of the cholesteric pitch allows us to probe the effect of the photonic band structure on spontaneous emission in a wide angular range. We find exceptional angular-dependent intensity and polarization variations of the emitted light and give experimental proof for the splitting of the first-order reflection band as well as its overlap with the second-order band at large detection angles.