Preparation And Property Of Heterostructured Quantum Dots

Heterostructured QDs was successfully synthesized via an anionexchange where Te2-in water-soluble CdTe QDs was partly replaced by S^2-.Factors such as reaction temperature and the ratio of S^2-/CdTe that affect thestructures and properties of resulted QDs had been investigated.1. Preparation and characterizations of CdTe QDs: CdTe QDs weresynthesized through an aqueous route. The particle size and crystallity of CdTeQDs were tuned by changing the refluxing time. UV-Vis and PL spectrumconfirmed that both the size and photoluminescence quantum yields (PLQY)of CdTe QDs were increased when prolonging the refluxing time.2. Preparation and characterizations of heterostructured QDs: Bycontrolling the reaction conditions, heterostructured QDs with controlledstructure and properties were obtained. The resulted QDs were characterizedby HRTEM, XRD, XPS, UV-Vis spectrum and PL spectrum.(1) The effect of the reaction temperature: CdTe QDs and S^2-were reactedat different temperature. Characteriazations showed that the optical propertiesof the resulted QDs were greatly influenced by the reaction temperature. At the lower temperature, both the UV-Vis and PL spectrum of the resulted QDswere blue shift and the PLQY enhanced significantly compared with CdTeQDs while prolonging the reaction time. However, at the higher temperature,both the UV-Vis and PL spectrum of the resulted QDs were red shifted,whereas the PLQY showed a first increase followed by decreases asprolonging the reaction time.(2) The effect of the ratio of S^2-/CdTe: The effect of the ratio of S^2-/CdTeon the optical properties of the resulted QDs was investigated at a constanttemperature. At the lower temperature, both the UV-Vis and PL spectrum ofthe resulted QDs showed the same blue shift with remarkable increase inPLQY. This indicats that, at the lower temperature, temperature has largeeffect on the reaction, while the ratio of S^2-/CdTe has almost no effect on thereaction. By contrast, the optical properties of the resulted QDs wereinfluenced more by the ratio of S^2-/CdTe with increasing the reactiontemperature. At the higher temperature, both the UV-Vis and PL spectrum ofthe resulted QDs were red shift and the PLQY increased first and thendecreased with prolonging the reaction time. Moreover, the degree of red shiftenhanced and the PLQY decreased more quickly with increasing the ratio ofS^2-/CdTe.(3) A model where the structure and properties of quantum dots can becontroled by tuning the rate of iron exchange reaction was proposed.