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

Abstract

Here we report a new “green” method to synthesize Zn_{1 −} xCd_xSe (x = 0–1) and stable red–green–blue tricolor Zn_{1 −} xCd_xSe core/shell nanocrystals using only low cost, phosphine-free and environmentally friendly reagents. The first excitonic absorption peak and photoluminescence (PL) position of the Zn_{1 −} xCd_xSe 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 Zn_{1 −} xCd_xSe 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/ZnSe_xS_{1 − x} and CdS/Zn_{1 −} xCd_xS have been found as an excellent middle multishell to overcoat between the alloyed Zn_{1 −} xCd_xSe core and ZnS outshell. The QYs of the as-synthesized core/shell alloyed Zn_{1 −} xCd_xSe nanocrystals can reach 40–75%. The Cd content is reduced to less than 0.1% for Zn_{1 −} xCd_xSe core/shell nanocrystals with emissions in the range 456–540 nm. More than 15 g of high quality Zn_{1 −} xCd_xSe 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.