Lifetime differences between the two emitted circular polarizations in Eu⁺³ based systems

Circularly polarized luminescence (CPL) spectroscopy is a measure of the degree of circular polarization in luminescence used to characterize chiral systems. Our work probes the luminescence lifetime differences between the two circular polarizations in chiral lanthanide based systems. Previous works in the field performed on organic luminophores with emission dissymmetry (g_lum=(I_L-I_R)/(I_L+I_R), where I_L and I_R are the left- and right-handed circularly polarized emission intensities, respectively) <1% and different lifetime scales (ms to ns) found no differences in lifetime between the two emitted circular polarizations. Lanthanide based chiral systems may have extraordinarily high (>10%) emission dissymmetries. This allowed us to measure lifetime differences between the two emitted circular polarizations in Eu⁺³ based chiral systems. We measured two Eu³⁺ complexes; CsEu(hfbc)₄ and Eu(facam)₃ (400-200us), and Eu³⁺ doped TbPO₄●D₂O nanocrystals (1.5ms). We found that dissymmetry magnitudes and differences in lifetimes are correlated: emission lines with negligible dissymmetry show zero difference in lifetimes, and emission lines with high dissymmetry display lifetime differences in most of the cases. We attribute this to competing non-radiative decay pathways, which are insensitive to the chirality. If these are much stronger than the radiative rate, then the contribution of the radiative rate to the differences in lifetimes becomes negligible.