Photoemission study of highly luminescent InP nanocrystals

Two kinds of strongly luminescent materials based on monodisperse colloidal InP nanocrystals were investigated by photoelectron spectroscopy with the use of synchrotron radiation. One method to achieve high photoluminescence quantum yields is the epitaxial overgrowth of a shell of a wider band gap semiconductor on the surface of the InP nanocrystals. We have studied InP nanocrystals covered with ZnS. The XPS results confirmed the core-shell structure of the composite nanocrystals and allowed us to extract the average layer thickness of the ZnS shell. Another approach to prepare highly luminescent nanoparticles is etching the nanocrystal surface with certain fluorine compounds. We have investigated InP nanocrystals treated with hydrogen fluoride. High resolution In 3d and P 2p core level spectra of etched and non-etched particles reveal changes at the nanocrystal surface. A simple model for the etching process is discussed.