Luminescence and growth of CdTe quantum dots and clusters

Highly luminescent CdTe quantum dots (QDs) were synthesised in a mixture of TOP and DDA. The growth of the particles in the reaction mixture was followed in time for three different temperatures. The reaction temperature determined the final diameter of the QDs (2.4 nm at 145 °C, 2.7 nm at 165 °C and 2.9 nm at 180 °C). For all three temperatures a fast initial growth is observed in the first 30 min and is followed by a slower growth to the final particle size. The small particles that are initially formed show a defect related emission. After several minutes an excitonic emission is observed. The quantum efficiency gradually increases from 10% to 45% for the best samples (after four hours). A good correlation between quantum efficiency and luminescence lifetime is observed. A luminescence lifetime of approximately 10 ns is found for the exciton emission in the CdTe particles with the highest quantum efficiency. The formation of small CdTe clusters of discrete sizes from Cd and Te precursors is observed in the reaction mixture at room temperature. The stability of the CdTe clusters depends on the reaction conditions and a stepwise growth from a smaller to a larger cluster size is observed.