title: Size reduction of CdSe/ZnS core-shell quantum dots photosensitized by benzophenone: where does the Cd(0) go?
abstract: The size of core-shell CdSe/ZnS quantum dots can be decreased by using the combined action of an n,π* aromatic ketone and UVA light. Energy-dispersive X-ray spectroscopy as well as X-ray photoelectron spectroscopy techniques gave information on the photosensitization mechanism and the eventual destiny of Cd(2+) and Se(2-) core ions. Our data support the electron transfer from the BP ketyl radical to Cd(2+), leading to Cd(0) and H(+), as well as to the recovery of benzophenone. Elemental Cd remains on the core and, eventually, can be oxidized to CdO. In addition, Se(2-) counterions disperse inside the solution mainly attached to protonated amine ligands. The Se(2-) combines with H(+), leading to SeH(2), which is finally oxidized to Se(0) by oxygen. Therefore, quantum dots illumination in the presence of benzophenones brings about a profound nanoparticle reconstruction which takes place after dark storage; this agrees with the drastic quenching of the quantum dot emission detected immediately after illumination as well as the slow recovery in the dark.
authors.affiliation: Department of Analytical Chemistry, Research Building, University of Valencia, Dr. Moliner 50, 46100, Burjassot, Valencia, Spain. raquel.galian@uv.es
authors.forename: Raquel E
authors.initials: RE
authors.lastname: Galian
authors.forename: Miguel
authors.initials: M
authors.lastname: de la Guardia
authors.forename: Julia
authors.initials: J
authors.lastname: Pérez-Prieto