ABSTRACT
More recently, people have been investigating the use of colloidal nanocrystals in applications ranging from biological markers12 to their use as chromophores in light-emitting diodes,13-16 dye-sensitized solar cells,17,18 and photovoltaics,19,20 and as charge transport materials in £eld-e¢ect transistors.3 In order to utilize colloidal nanocrystals in these applications, it has become increasingly important to determine how the local environment21,22 and the surface chemistry of the nanocrystals can a¢ect the optical and electronic properties of individual nanocrystals and nanocrystal £lms. –e surface of a CdSe nanocrystal is capped with either an inorganic shell of a wider band gap material (i.e., CdS, ZnS) in order to con£ne excitons to the core of the nanocrystal or the surface is capped with organic ligands (Figure 11.1). Inorganic shells and organic ligands that are used to cap a nanocrystal can alter the photoluminescence of the nanocrystal by (1) creating or passivating charge trap states on the nanocrystal surface, (2) forming an insulating, dielectric layer around the nanocrystal, (3) acting as electron or hole acceptors, or (4) allowing energy transfer between the ligands and nanocrystal (increasing or decreasing
11.1 Introduction ......................................................................................307 11.2 Colloidal Nanocrystal Photoluminescence ..................................309 11.3 Quenching by Surface States ........................................................... 311 11.4 Ligand-Nanocrystal Binding Constants ......................................312 11.5 Nanocrystal Photoluminescence Quenching by Charge
and Energy Transfer ......................................................................... 314 11.6 Nanocrystal Intraband Charge Relaxation ..................................315 11.7 Nanocrystal Photoluminescence Intermittency .......................... 317 References ...................................................................................................... 318
the nanocrystal photoluminescence). –is chapter will describe the current understanding of colloidal CdSe and CdS nanocrystal photoluminescence and how nanocrystal photoluminescence can be a¢ected by the capping ligands and the local environment of the nanocrystals.
