Large scale synthesis of stable tricolor Zn1-xCdxSe core/multishell nanocrystals via a facile phosphine-free colloidal method

Here we report a new green method to synthesize Zn-1 (-) xCdxSe (x = 0-1) and stable red-green-blue tricolor Zn1 - xCdxSe core/shell nanocrystals using only low cost, phosphine-free and environmentally friendly reagents. The first excitonic absorption peak and photoluminescence (PL) position of the Zn1 - xCdxSe nanocrystals (the value of x is in the range 0.005-0.2) can be fixed to any position in the range 456-540 nm. There is no red or blue shift in the entire reaction process. Three similar sizes of alloyed Zn1 - xCdxSe nanocrystals with blue, green, and yellow emissions were successfully selected as cores to synthesize high quality blue, green, and red core/shell nanocrystal emitters. For the synthesis of core/shell nanocrystals with a high quantum yield (QY) and stability, the selection of shell materials has been proven to be very important. Therefore, alternative protocols have been used to optimize thick shell growth. ZnSe/ZnSexS1 - x and CdS/Zn1 - xCdxS have been found as an excellent middle multishell to overcoat between the alloyed Zn1 - xCdxSe core and ZnS outshell. The QYs of the as-synthesized core/shell alloyed Zn1 - xCdxSe nanocrystals can reach 40-75%. The Cd content is reduced to less than 0.1% for Zn1 - xCdxSe core/shell nanocrystals with emissions in the range 456-540 nm. More than 15 g of high quality Zn1 - xCdxSe core/shell nanocrystals were prepared successfully in a large scale, one-pot reaction. Importantly, the emissions of such thick multishell nanocrystals are not susceptible to ligand loss and stability in various physiological conditions.