A novel organometallic synthesis of highly luminescent CdTe nanocrystals

Highly luminescent CdTe nanocrystals were synthesized by reacting dimethylcadmium with different tellurium sources in mixtures of dodecylamine and trioctylphosphine as the coordinating and size-regulating solvent. Colloids of crystalline CdTe nanoparticles with zinc blende lattice displaying mean particle sizes between 2.5 and 7 nm were prepared at temperatures from 150 to 220 degreesC and were characterized by powder XRD, HRTEM, absorption, and luminescence spectroscopy. The particles show strong band-edge photoluminescence shifting from green to red with increasing particle size. The photoluminescence quantum yield was found to strongly depend on the tellurium source employed in the synthesis. The highest quantum yields were observed by using a suspension of tellurium powder in a mixture of dodecylamine and trioctylphosphine. These CdTe samples show a photoluminescence quantum yield up to 65% at room temperature without covering the surface of the nanoparticles with a passivating inorganic shell. If a solution of tellurium in TOP rather than tellurium powder is used, higher reaction yields but nanoparticles with lower quantum yields (about 35-50%) are the result. As-prepared colloids show rather narrow particle size distributions, although all reactants were mixed at low temperature. The size distributions can be further improved by standard size selective precipitation.