Narrow Blue Emission from Cadmium Phosphide Clusters Enhanced through Phosphinate Ligation

The atomic precision of magic-sized clusters offers a route toward narrow emission by eliminating heterogeneous broadening. Herein, we report ultra-narrow 467 nm blue emission from cadmium phosphide clusters with a 96 meV line width and as high as 26% photoluminescence quantum yield (PLQY) enabled by tightly bound, bidentate phosphinate ligands. They are obtained through post-synthetic ligand exchange from the starting oleate-capped clusters. The phosphinate maintains the bidentate coordination motif, which does not disturb the metastability of the material but does induce a change in the surface dipole, causing a bathochromic shift in the emission from 457 nm to 467 nm, which is an optimal wavelength for blue emission. We find that the structure of the ligand tail can heavily influence PLQY and other aspects of the charge carrier dynamics. The ligand exchange protocol can also be applied to the related cadmium arsenide clusters, resulting in similarly narrow 550 nm green emission with a 9% PLQY.