Synthesis of Magic-Sized CdSe and CdTe Nanocrystals with Diisooctylphosphinic Acid

We report the observation of quantized growth in magic-sized CdSe and CdTe nanocrystals that utilize diisooctylphosphinic acid as the surface passivating ligand. The interaction between the diisooctylphosphinic acid and the coordinating solvent, hexadecylamine, results in the growth of only certain allowed sizes of nanocrystals. Magic-sized CdSe nanocrystals were synthesized with band edge absorption peaks at 414, 446, and 490 nm. Magic-sized CdTe nanocrystals were synthesized with band edge absorption peaks at 445 and 483 nm. The synthesis detailed here allows for the isolation of larger magic-sized nanocrystals than has been previously reported. The emission of diisooctylphosphinic acid-capped magic-sized nanocrystals is low, with a quantum yield of less than 1%. Photoluminescence excitation scans revealed a significantly reduced emission from absorption at the band edge. The diameter for the smallest CdSe magic-size was 1.7 nm, and the diameter for the smallest CdTe magic-size was 1.8 nm, as determined by transmission electron microscopy.