Optical properties of colloidal core/shell nanocrystals

Recently, colloidal core/shell nanocrystals have found use in several applications such as solar cells, light emitting diodes, fluorescent dies, etc. In this thesis, optical properties of colloidal CdSe/ZnS core/shell nanocrystals were studied. The samples were prepared such that the nanocrystals were embedded in a UV curable resin. Once the samples were cured, they were placed in different spectrophotometers to measure the absorbance and the photoluminescence (PL) spectrum. The effect on the absorbance and PL spectra was investigated by using nanocrystal samples of different quantum dot sizes and by changing the temperature of the samples. It was found that the energy band gap of the nanocrystal structures tends to increase as the nanocrystal diameter decreases. The energy band gap also decreases as the temperature of the nanocrystal sample increases. The Stokes shift (the difference between the absorbance and PL peaks) was found to increase as the nanocrystal diameter decreases. Through calculations, it was determined that the electron-phonon coupling increases as the nanocrystal diameter decreases. Finally, Debye and Einstein temperatures are calculated analytically and their ratio was found to be close to unity