Nanocellulose chiral synergistic effect enhances circularly polarized luminescence of lanthanide electric dipole transition bands

The circularly polarized luminescence (CPL) of Eu³⁺ ions have been highly valued due to their high asymmetry factor and characteristic luminescence. However, most of the CPL of Eu³⁺ ions is contributed from the magnetic dipole transitions and much less is from the electric dipole transitions due to the influence of coordination fields. Until now, the amplification of the asymmetry factor (g_lum) of CPL is mainly due to magnetic dipole transition g_lum (g_lum-mag), while electric dipole transition g_lum (g_lum-ele) has almost no amplification. In this study, nanocellulose chiral films were synergistically induced with chiral β-diketones Eu-TFC (d/l) and hybrid photonic crystal films CNC@Eu-TFC (d/l) targeted methods for achieving electric dipole transition CPL and g_lum-ele of Eu³⁺ ions. The g_lum-ele was higher than g_lum-mag, achieving a reversal of g_lum-ele and g_lum-mag sizes. The g_lum of CNC@Eu-TFC (l) was relatively higher than that of CNC@Eu-TFC (d), the main reason for which was that the macroscopic chirality of the nanocellulose film, with a left-handed spiral structure, had a stronger synergistic induction effect with left-handed Eu-TFC (l). Therefore, utilizing the macroscopic chirality of CNC films could effectively amplify the difficulty to activate g_lum-ele of Eu³⁺ ions, providing a new approach for its preparation in high-performance CPL materials.