| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 91 === The synthesis, optical and structure properties of Ⅱ-Ⅵ group semiconductor nanocrystal (quantum dots) are investigated and the core-shell structures of the quantum dots exhibit interesting effects on optical properties. To comprehend optical and structure properties through UV-Vis absorbance spectra, photoluminescence spectra, X-ray diffraction spectra, TEM pictures.
To prepare quantum dots of CdSe and CdSe/ZnSe core-shell structure in chemical colloidal synthesis. At fixed Cd/Se molar ratio, the same reaction temperature, Kinetic control reaction time to produce different size quantum dots. The narrow size distribution were reached due to the mechanism of nucleation and growth.
In optical properties, CdSe and CdSe/ZnSe core-shell structure have quantum confinement effects. It means the band gap of nanocrystals decreases as their size increases. There is red shift phenomenon in absorbance and PL spectra. In addition, we can use a formular to compute particle size. Photoluminescence quantum yield values were measured relative coumarine 6. Coumarin 6 is an organic dye. To obtain Q.Y. values, we need the data from absorbance and PL spectra. It could indirectly prove the formation of CdSe/ZnSe core-shell structure via the raise of Q.Y.
In structure properties, CdSe is wurtzite structure, hexagonal closet packing. It conforms with theoretical values in XRD pattern. In XRD pattern, there are CdO’s peaks. It means that CdO reacts incompletely. The peaks are not shift but broading in CdSe/ZnSe core-shell structure’s XRD pattern. We figure CdSe overcoated with a potion ZnSe. The whole core-shell structure may not form yet. There are only TEM pictures of reaction time equal to twenty minutes. From these pictures, we estimate the particle sizes equal to 5nm. The result is to fit in with the data from absorbance spectra. As for CdSe/ZnSe core-shell structure, we need HR-TEM to see lattice images to prove directly the formation of core-shell structure.
|
|---|
