On the circular polarization of fluorescence from dyes dissolved in chiral nematic liquid crystals

The sense of circular polarization of the fluorescence from dyes dissolved in chiral nematic liquid crystals (CNLCs) with a photonic stopband overlapping the dye emission (`resonance regimeʹ) displays a peculiar reversal as a function of wavelength, which so far is not satisfactorily explained. We systematically study this phenomenon and show that theories based on the guest/host alignment of the fluorescent dye in the CNLC matrix are not adequate in the resonance regime. We instead propose a consistent explanation of sign reversal based on the description of CNLCs as one-dimensional (1D) photonic crystals.