Dark-red-emitting CdTe/Cd1-x Znx S core/shell quantum dots: preparation and properties.

CdTe nanocrystals (NCs) were fabricated through an organic synthesis. The growth and properties of CdTe NCs depended strongly on the preparation conditions. In a reaction system of octadecene and tetradecylphosphonic acid (TDPA), the growth was slow. CdTe NCs with cubic-like morphology were created in trioctylamine (TOA) using octadecylphosphonic acid (ODPA)-CdO or TDPA-CdO as precursors. The TOA and ODPA system gives rise to NCs with high photoluminescence (PL) efficiencies (12%). A Cdx Zn1-x S shell coating on the CdTe core, gave rise to tunable dark red PL (630-670 nm). The morphology and PL properties of the CdTe cores were drastically affected by shell coating and this determined the properties of CdTe/Cdx Zn1-x S NCs. Small CdTe NCs were easily coated with Cdx Zn1-x S shells. The resulting core/shell NCs revealed a spherical morphology. However, shell growth became slow when large CdTe cores were used. This is ascribed to the cores with a cubic-like morphology. CdS interlayer plays an important role for the formation of the CdTe/Cdx Zn1-x S NCs because the experimental result indicated it is difficult to coat CdTe NCs with a ZnS shell. The core/shell NCs benefited from a Cdx Zn1-x S composite shell because CdTe/CdS NCs created via a similar procedure revealed a low PL efficiency.