Circularly polarized and total luminescence as probes of nucleation and growth in chiral nanocrystals

Nucleation of crystals as well as their growth is difficult to study experimentally. We have recently demonstrated that chiral Eu³⁺-doped terbium phosphate nanocrystals are an interesting system for studying nanocrystal formation mechanisms and chiral symmetry breaking, occurring during their formation, directed by chiral ligands, such as tartaric acid. In this paper, we show how simultaneous, in situ monitoring of both total emission intensity and circularly polarized luminescence magnitude and sign versus time during nanocrystal formation provides considerable information on the mechanisms of nanocrystal nucleation and growth. Specifically, we show that the presence of tartaric acid leads to the formation of chiral prenucleation clusters, which deterministically transform into nanocrystals of a specific handedness. Additionally, we demonstrate that both unseeded and seeded nanocrystal syntheses behave differently mechanistically and that the addition of seed nanocrystals catalyses both enantio-specific (also called secondary nucleation) as well as nonspecific nucleation.