| abstract |
The present invention provides new compositions containing colloidal nanocrystals with high photoluminescence quantum yields, new synthetic methods for the preparation of highly luminescent colloidal nanocrystals, as well as methods to control the photoluminescent properties of colloidal nanocrystals. For example, this invention encompasses as-prepared nanocrystals that luminesce from about 550 nm to about 675 nm and exhibit a photoluminescence quantum yield (PL QY) greater than or equal to about 40%. In some embodiments, PL QY from about 50% to about 80% are obtainable for nanocrystals that luminesce from about 600 nm to about 650 nm. The new synthetic methods disclosed herein allow photoemission brightness (quantum yield) to be correlated with certain adjustable nanocrystal growth parameters associated with a given synthetic scheme. The PL QY of as-prepared CdSe (and other) semiconductor nanocrystals increases monotonically with time in the early stages of the crystallization process, and then gradually decreases after attaining a maximum point. The time at which a maximum PL QY is attained is referred to as the PL bright point. The position of this bright point, the PL QY value at the bright point, the FWHM of the PL spectra, and several other parameters of the growth process of the CdSe nanocrystals are all strongly dependent on the initial Cd:Se ratio of the precursors in the solution, and certain other experimental parameters. This bright point is different from the point of minimum polydispersity of the nanocrystal sample, referred to as the focusing point of size distribution. CdSe nanocrystals synthesized by this alternative method represent a series of excellent emitters in the orange-red color window in terms of their PL QY, the FWHM of the PL spectra, and the stability of the emission. |