Optical and electronic properties of type-II CdSe/CdS core–shell quantum dots

CdSe/CdS core–shell quantum dots (QDs) were synthesized using a facile method in aqueous phase. X-ray diffraction pattern, high-resolution transmission electron microscopy images, and energy dispersive spectroscopy profiles showed that stoichiometric CdSe/CdS QDs were formed. Temperature-dependent photoluminescence spectra showed that the activation energy of CdSe/CdS core–shell QDs was 15 meV. The potential profiles and interband transition energies of the strained type-II CdSe/CdS core–shell QDs were calculated. The calculated interband transition energies slightly decreased from 2.061 to 2.007 eV when the shell thickness increased from 10 to 17 A. The theoretical interband transition energy of 2.007 eV was in reasonable agreement with the photoluminescence excitonic transition energy of 1.98 eV.