Energy level tuning of InP/ZnS nanocrystals by electronically delocalized dithiocarbamate derivatives

Abstract

The nanocrystals have characteristics of varying the energy gap between the valence band and the conduction band depending on the size, and are attracting attention as light emitting materials due to the excellent in light stability. Since the bandgap of nanocrystals is determined by the size, it is very important to control the size of the nanocrystals in order to realize the red, green and blue primary color in a display. However, there are many difficulties in finely adjusting the nanocrystal bandgap to a size. In this study, the monodentate amine ligands coordinated on the surface of InP/ZnS nanocrystals are substituted with bidentate dithiocarbamate ligands having a strong coordination ability and electrically resonant structures, so that the nanocrystal can be finely tuned to control the emission spectrum. NMR analysis showed that some amine ligands on the surface of the nanocrystals were substituted with dithiocarbamate ligands. The PL spectra also show that the emission wavelength of the new nanocrystals is increased by about 20 nm (bathochromic shift), indicating that the active region of the exciton (an electron-hole pair) is extended to the delocalized dithiocarbamate ligands as well as the nanocrystals.