PLE spectra analysis of the sub-structure in the absorption spectra of CdSeS quantum dots

The semiconductor CdSeS quantum dots (QDs) embedded in glass are analysed bymeans of absorption spectra, photoluminescence (PL) spectra andphotoluminescence excitation (PLE) spectra. The peaks of absorption spectrashift to lower energies with the size of QD increasing, which obviouslyshows a quantum-size effect. Using the PLE spectra, the physical origin ofthe lowest absorption peak is analysed. In PLE spectra, the lowestabsorption peak can be deconvoluted into two peaks that stem from thetransitions of 1S_3/2--1S_e and 2S_3/2--1S_e respectively.The measured energy difference between the two peaks is found to decreasewith the size of QD increasing, which agrees well with the theoreticalcalculation for the two transitions. The luminescence peak of defect statesis also analysed by PLE spectra. Two transitions are present in the PLE,which indicates that the transitions of 1S_3/2--1S_e and 2S_3/2--1S_e are responsible for the defect states luminescence.