Electroabsorption Spectra of Quantum Dots of PbS and Analysis by the Integral Method

Electroabsorption (E-A) spectra of semiconductor quantum dots (QDs) of PbS have been analyzed by the integral method, which is powerful not only to determine the change in electric dipole moment and/or polarizability following absorption precisely but also to confirm the weak absorption bands buried under other strong absorption bands. In the results, two weak absorption bands which induce blue-shift and red-shift, respectively, with application of electric fields have been newly confirmed in PbS QDs to be located just above the intense first exciton band. The energy separation between these two bands becomes smaller, as the applied field strength becomes stronger, suggesting that the interaction between the states excited by these transitions becomes weaker by application of electric fields. The QD size dependence has been reported both for the transition energy and for the magnitude of the change in electric dipole moment and molecular polarizability following the absorption of each band. The assignment of the absorption bands has also been discussed.