Studying the size-selective precipitation of colloidal quantum dots by decomposing the excitation-emission matrix

The exciton peak in the excitation-emission matrix (EEM) of colloidal quantum dots implicitly contains information about inhomogeneous broadening and the photoluminescence (PL) and photoluminescence excitation (PLE) spectra of individual particles in the vicinity of the absorption onset. A numerical procedure for extracting this information has been developed and applied to the EEMs of polydisperse InP/ZnS core/shell colloidal quantum dots and their supernatant solutions obtained by partial precipitation with a non-solvent. The inhomogeneous broadenings obtained in this way have been converted by the sizing curve into particle-size distributions. These distributions have been found to be in agreement with the size-selective precipitation theory proposed recently. The homogeneous PL and PLE line shapes obtained by analyzing the EEMs were found to satisfy the Kennard-Stepanov relation, which is the first more or less direct evidence of its validity for colloidal quantum dots.