CHARACTERIZATION OF CdSe CORE AND CdSe/ZnS CORE/SHELL QUANTUM DOTS SYNTHESIZED USING A MODIFIED METHOD

In this work we have performed a modified organometallic method for synthesis of CdSe core and CdSe/ZnS core/shell quantum dots of different sizes at room temperature. In this organometallic scheme, one-pot synthesis of core/shell nanocrystalls in HDA-TOPO-TOP mixture is used. The structural features were determined with x-ray powder diffraction and all direction peaks are consistent with the wurtzite structure. The results of x-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) revealed that the prepared CdSe/ZnS quantum dots QDs had a core/shell structure with high crystallinity. The estimated average of the particle size was found to be 3.10 nm for core and 4.25 nm for core/shell by a TEM image. The average sizes of QDs were also estimated by using various ways such as the Sherrer's formula and the Yu et al theoretical expression. The obtained CdSe and CdSe/ZnS nanocrystals were characterized by using UV-vis spectroscopy which confirmed that a series of CdSe/ZnS particles with diameter of 3.52 - 4.25 nm, corresponding to the first peak of absorption spectra in 570 - 592 nm range, were successfully achieved. Shell formation was confirmed by observation of red shift in the UV-vis absorption spectra. The optical band gap of CdSe/ZnS nanoparticles decreased from 2.70 to 2.10 eV with an increasing in the particle size due to change of shell thickness. The narrow photoluminescence from these composite dots spanned most the visible spectrum from blue through red with quantum yields of 30-40 % at room temperature. All the prepared samples have semiconducting behavior and can be used in the field of solar cell and light emitting diodes.