Circularly Polarized Photoluminescence from Gradient-Pitch Chiral-Nematic Films

Abstract

A mixture consisting of a nematic acrylate and a chiral diacrylate lightly doped with Exalite 428, a laser dye, was prepared into thin films for in situ photopolymerization. The laser dye served to regulate the photocuring intensity profile into the film and as a light emitter. With optimized chemical composition, photocuring intensity, and temperature, a gradient-pitch film with a broad resonance band was produced to cover the emission peak of the laser dye. The SEM image provided new insight into the distribution of pitch length across the film thickness, consistent with the selective reflection spectra. Upon UV excitation, the observed sense and degree of circularly polarized photoluminescence were qualitatively interpreted on the basis of the photoexcitation intensity received by the dopant molecules and by the wavelength-dependent interaction of emitted light with an asymmetric structure.